An introduction to Berkeley UNIX and ANSI C 0130684953

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NTRODUCT

Berkeley UNIX and ANSI C

JACK HODGES

STUDENT INFORMATION Name First

Middle

Last

Street

Apt.

CityZipcode

Account ID: Address

Telephone

Area Code

HOST INFORMATION Login Host Symbolic

Name

Login Host IP Address

Modem Numbers/Baud

Rates:

COURSE INFORMATION Laboratory Locations/Hours:

Laboratory Assistant Name:

_

Laboratory Assistant Userid:

Laboratory Assistant Office/Hours:

Instructor

Name:

Instructor Userid:

Instructor Office/Hours:

Instructor Phone:

'

PRENTICE HALL. Englewood Cliffs,

N.J.

07632 -

Library of Congress Cataloging-in-Publication Data

Hodges, Jack.

An

introduction to Berkeley

UNIX

and

ANSI C

/

Jack Hodges.

cm.

p.

Includes index.

ISBN 0-13-068495-3 1.

Berkeley UNIX.

2.

Operating systems (Computers)

(Computer program language) QA76.76.063H637 1995

I.

3.

C

Title.

94-24249

005.4'3--dc20

CIP

Acquisitions editor: Bill Zobrist

Production editor: Bayani Mendoza de Leon editor: Andrea Hammer Cover designer: Rich Dombrowski Buyer: Lori Bulwin

Copy

Editorial assistant: Phyllis

©

Morgan

1995 by Prentice-Hall,

Inc.

A Simon & Schuster Company Englewood Cliffs, New Jersey 07632 No part of this book may be any form or by any means, without permission in writing from the publisher. All rights reserved.

reproduced,

in

The author and publisher of

this book have used their best efforts in preparing this book. These efforts include the development, research, and testing of the theories and programs to determine their effectiveness. The author and publisher make no warranty of any kind, expressed or implied, with regard to these programs or the documentation

contained in this book. The author and publisher shall not be liable in

connection with, or arising out

of, the furnishing,

in any event for incidental or consequential damages performance, or use of these programs.

The use of trade names, trademarks, etc., even if not specially identified, should not be construed that such names are not protected by the Trade Marks and Merchandise Marks Act. Printed in the United States of

10

987654321

America

ISBN D-13-abflMTS-3

Prentice-Hall International

(UK) Limited, London Sydney

Prentice-Hall of Australia Ply. Limited,

Prentice-Hall

Canada

Inc.,

Toronto

Prentice-Hall Hispanoamericana, S.A., Prentice-Hall of India Private Limited,

Prentice-Hall of Japan, Inc.,

Simon

&

Mexico

New

Delhi

Tokyo

Schuster Asia Pie. Lid., Singapore

Edilora Preniice-Hall do Brasil, Ltda., Rio de Janeiro

as an indication

1

Preface

xi

Parti

UNIX

1

The Login Session 1

.

1.2

Introduction and Scope

3

Terminal and Console Login

4 6

1

.3

Logging on

1

.4

Changing Your Password

1.5

2

3

to a

Host

9

Logging Out

11

1

.6

Dialup Login and Terminal Servers

12

1

.7

Exercises and Sample Quiz Questions

16

Electronic

Communications

17

2.1

Introduction and Scope

17

2.2

Sending and Receiving Electronic Mail

19

2.3

Using the

UNIX

mail Utility

23

III

IV

3

4

5

Table of Contents

2.4

MH — The RAND Mail Handler

35

2.5

Problems Replying

40

2.6

Electronic Talk

2.7

Electronic

2.8

Exercises and Sample Quiz Questions

The UNIX

File

File

to

Email

42

News

45

System

53

57

3.1

Introduction and Scope

3.2

File

3.3

UNIX Commands

61

3.4

Directories and Directory Manipulation

67

3.5

Files

3.6

Filesystem Security

93

3.7

Exercises and Sample Quiz Questions

99

57

System Components

58

and File Manipulation

Creation and Editing

81

101

4.1

Introduction and Scope

101

4.2

File Editing

102

4.3

The

102

4.4

The emacs Editor

4.5

Text Alteration: emacs

4.6

Exercises and Sample Quiz Questions

130

4.7

Recommended Reading

131

vi

Full-Screen Editor

The UNIX Command

Shell

1

Command Mode

and Process Control

15

123

133

5.1

Introduction and Scope

133

5.2

The Login

134

5.3

Shell Control

150

5.4

Command

163

5.5

Linking Files and Directories

Shell Scripts

Manipulation

168

1

6

7

File

5.6

Exercises and Sample Quiz Questions

170

5.7

Recommended Reading

172

Formatting and Printing

173

6.1

Introduction and Scope

173

6.2

Printing Etiquette

174

6.3

Printing Tools

175

6.4

Printing a

6.5

Laser Printing in Draft

6.6

Text Formatters

6.7

nroff and troff

187

6.8

Online Documentation using nroff

198

6.9

LATEX

203

6.10

Exercises and Sample Quiz Questions

222

6.

Recommended Reading

225

1

Document

Mode versus Word

179 1

Processors

Network Processing

82

185

227

7.1

Introduction and Scope

227

7.2

Shared Resources and Network Etiquette

228

7.3

Single-User Status

229

7.4

Network-User Status

234

7.5

Network

239

7.6

Remote Processing

7.7

File

7.8

Exercises and Sample Quiz Questions

261

7.9

Recommended Reading

262

Status

System Management

241

251

1

VI

Table of Contents

Part

II

Programming Languages and ANSI C

8

9

Introduction to

C Programming

8.1

Introduction and Scope

265

8.2

Programming Languages

266

8.3

The C Programming Language

267

8.4

C

288

8.5

Variable Type Conversion

294

8.6

Program Layout and Organization

295

8.7

Style for

8.8

Exercises and Sample Quiz Questions

Types, Operators, and Expressions

C Program

Layout

Decision Making, Iteration, and Functions

10

265

295

297

299

9.

Introduction and Scope

299

9.2

Making Decisions

300

9.3

Iteration

311

9.4

Functions

318

9.5

Exercises and Sample Quiz Questions

339

Arrays, Structures, and Files

341

10.1

Introduction and Scope

341

10.2

Comparing

342

10.3

Array Variables

10.4

Structured Variables for Unlike Data Types

351

10.5

Exercises and Sample Quiz Questions

360

Iterations

Using Arrays

in File

Operations

347

1

VII

11

Programming Tools 1

1

1

1.2

.

11.3 1 1

.4

11.5 1

1.6

11.7

363

Introduction and Scope

363

Debugging a C Program

364

Program Debugging

370

Debuggers

380

Developing Program Libraries

385

Organizing and Maintaining Complex Programs

387

Recommended Reading

395

Part

UNIX

12

13

Shell

III

Programming

Regular Expressions and Scripts

C

399

12.1

Introduction and Scope

399

12.2

Regular Expressions

400

12.3

egrep

408

12.4

awk

409

12.5

sed

417

12.6

Exercises and Sample Quiz Questions

423

425

Shell Scripts

13.1

Introduction and Scope

425

13.2

Shell Script Execution

426

Shell Script Variables

427

13.6

C C C C C

13.7

Exercises and Sample Quiz Questions

13.3

13.4 13.5

Arguments

429

Shell Script Creation and Execution

431

Shell Script Control Structures

435

Shell Script

446

VI

I

Table of Contents

14

Bourne

449

Shell Scripts

14.1

Introduction and Scope

449

14.2

Invoking a Bourne Shell Script

450

14.3

Bourne Shell Variables

451

14.4

Bourne Shell Arguments

452

14.5

Bourne Shell Creation

455

14.6

Bourne Shell Control Structures

457

14.7

Exercises and Sample Quiz Questions

466

14.8

Recommended Reading

468

Appendices

A

Answers

to

Chapter

Sample Quiz Questions 1

- The Login Session

470

UNIX

472

File

System

Chapter 4 - File Editing Chapter 5 - The

Command

473 Shell

474

Chapter 6 - File Formatting and Printing

476

Chapter 7 - Networking

479

Chapter 8 Chapter Chapter Chapter Chapter

C Programming 9 - C Programming II 10 - C Programming III 12 - UNIX Programming Tools 13 - C Shell Programming I

Chapter 14 - Bourne Shell Programming

UNIX

469

Chapter 2 - Electronic Communications Chapter 3 - The

B

469

File

System

481

483

486

490 491

493

495

4 7

IX

c D E

Generic Login Session

Bare Bones UNIX

A Generic

Commands

Utility

496

497

499

mail as a Generic Utility

500

G

„ile

502

H

Execution Path

I

File

J

ASCII Characters

507

K

C Functions

508

L

L A T E X Templates

513

v

:

Editing as a Generic Utility

and Directory Permissions

L

.

I

L.2 L.3

L.4 L.5

The L A T E X Resume Template

505

506

5

1

E X Command File for Articles Executing latex on a Command File

5

1

A L T E X Sample Article or Research Paper A L A T E X Letter Command File

520

A

L AT

519

521

Table of Contents

L.8

L T E X Bibliography Examples L T E X Index Examples Other Features of T E X

L.9

Comparison

L.6 L.7

Index

to

HTML

523

526 527 528

535

Welcome ly

to

Berkeley

used version of

UNIX. The book

is

UNIX!

UNIX

This book

is

intended to introduce you to a wide-

called Berkeley

intended to teach you

System Distribution, or Berkeley to understand, use, and appre-

how

UNIX operating system. You any prior exposure to computers or to UNIX to succeed at learn-

ciate operating systems, and, in particular, the

need not have

The intention is that you gain sufficient facility with the mayou can extend your knowledge through experience on your own. Although this material has been left to the student to learn on his or her own in the past, we have found that some guidance is extremely helpful in showing ing this material.

terial that

you what can be done with the UNIX operating system and how it can benefit you when using any computer. At our institution, we run this as a self-paced laboratory course and recommend the adoption of this format elsewhere. This book

is

intended to accompany a one-semester introductory course in

learning about and using

UNIX

and

ANSI

C.

The

UNIX

large and diverse, so students are not expected to master

operating system it

in

is

one semester.

However, they are expected to learn the fundamentals of the operating system, as defined by the chapter headings in this book. They are also expected to use the operating system. Reading alone simply doesn't work. The students' knowledge of its use will probably be examined at a fairly shallow level, but

show expertise at that level. The book makes ommendations about how much depth should be covered in any particular they should be expected to

ic

rec-

top-

for this course.

Students are also being introduced to a powerful programming language.

They are not expected to master C, but are expected to learn the fundamentals of programming and to demonstrate the ability to program. This will include simple but correct use of syntax, programming style, debugging, and logic in simple program writing. As students read about the language and write their

XI

XII

Preface

programs, they should be encouraged

first

quisition of

new programming

C

about the similarities

to think

might share with other languages, because these

similarities will

make

the ac-

skills easier later.

To the Student There are four basic components

to

any computer:

( 1 )

hardware, (2) the oper-

The operating system tells the hardexecute which program on what data. A program is a

ating system, (3) programs, and (4) data.

ware how and when

to

series of instructions that manipulate data according to the semantics of a pro-

gramming language. Technically, an operating system

is

program or a

a

set

of

programs. Together, the operating system, programs, and data make up what is

called software. This

book

is

intended to teach you

ulate operating systems, programs,

and the interactions

that an operating

computer hardware,

and

data.

how

to use

and manip-

The elements of programming,

system mediates between the user and the

you learn

are generic. Thus, the concepts

book

in this

apply to any hardware platform, operating system, language, or data

The prevalence of the guage are widespread

UNIX

used today are

in

machines

that

version of

System V®,

you have access

to

System Distribution

XENIX®,

-

BSD.

and AIX®). Most of the

probably are or soon will be running some

UNIX.

BSD

dialect of the

UNIX

operating sys-

UNIX dialect in which many of the examples in this book were tested

tem. The

called Ultrix,

Different

which

UNIX

is

installed at this institution

dialects, particularly

command sets, utilities, and introduce UNIX, and to provide

intended to

on

DEC® VAX®

a

UNIX

Berkeley

slightly different is

Many operating systems being

derivatives (e.g.. Berkeley

This course introduces you to the

is

file.

UNIX operating system and the C programming lan-

academia and industry.

MACH®, A/UX®,

Ultrix®,

will

6420.

and System V. have

associated mind-sets. a comprehensive

set

The book

of tools for

UNIX. The examples in this book have been executed on severBSD-compatible UNIX hardware platforms, or hosts, (i.e., a computer that has a BSD-compatible operating system), so they should work for you.

those learning al

The C programming language

UNIX

is

implemented

that interact with the

UNIX

and they are often more This book tem.

(II)

the

is

is

widely used on

in (i.e.. written in) C.

Thus,

UNIX

it is

operating system and hardware

efficient than

programs written

in

topically divided into three parts: (I) the

C programming

language, and

(III)

UNIX

the following sections, the suggested organization

platforms because

easier to write programs

when

written in C.

other languages.

UNIX

shell

operating sys-

programming.

In

and administration of a

course that uses this book as a primary text or supplement will be presented.

HELP!

HELP!

— Related Materials

XII

— Related Materials There are

at least six

course on

UNIX

sources of information for the content of an introductory

and C.

•

This book and the sample quiz questions provided with each chapter.

•

UNIX

A

reference texts:

of references can be found

list

at the

end of selected

chapters in this book. •

A UNIX

•

C programming

examples worked out

director) that includes

in this text

and may be

helpful for experimentation and sample exercises.

A list of references can be found at the end of

reference texts:

selected chapters in this book.

UNIX

online manual pages.

•

The

•

Newsgroups:

We

have found

paced") to be a valuable tool

that a dedicated

in

newsgroup

(that

we

call "self-

disseminating information to the students tak-

ing this course on this campus. Because of the nature of such courses, a news-

group

is

Course

•

a valuable asset.

staff:

Uaboratory assistants and instructor. The information about

to reach these

people

is

how

generally furnished early in a course, preferably the

day.

first

The Book Each chapter

This book

is

concept

introduced, references are cited (e.g.. text page or

is

written in a modular format.

self contained:

is

man

A

page), tuto-

examples of how

rial

to use the concept are presented and discussed, and samknowledge of the material are given. Answers to sample provided in Appendix A. There is an index in the back of the

ple questions to test

questions are

book

How

for finding terms too specific for the table of contents.

to

Read This Book

Each chapter

in this

book

is

broken into sections. The

first

section always in-

troduces the topic and the scope of the topic on which the student should focus.

The

sections following introduce, discuss, and illustrate the facets of UNIX. C.

and so forth associated with the be

illustrative,

topic.

The examples provided

should be expected to experiment with the proficient at the level described will

be a table of related

the topic scope, and

commands

to all of the

is

utilities to

become

or

command options associated with the minimum expertise described in

exceeds the

presented to allow interested students to experiment

the topic without the explicit

section in a chapter

Answers

is

commands and

by the scope. At the end of many sections there

topic. This reference table often

more with

are intended to

and are not exhaustive of the scope of the chapter. Students

always the

sample

test

set

need for a

UNIX

reference.

of exercises and sample

problems can be found

in

test

The

last

problems.

Appendix A.

XIV

Preface

When

reading this book, references to other topics and locations will ap-

pear as (Chapter nn, Section nn, and page tion

number and

mm), where nn

is

the chapter or sec-

mm is a page number or range. Text references will appear in

[author year] format. Online manual references will appear as

where "com"

a

is

UNIX command

(man

com)

name.

Book Nomenclature Learning

UNIX

a screen.

To understand

is

best done at a keyboard, with the responses

book, you will need to understand what ferent ways.

Below you

you

UNIX

will see,

staring

and

we mean when we

to

this

at

you on

understand

this

display items in dif-

will find a listing of the terminology

nomenclature as they are found throughout

back

and the associated

book.

Book Nomenclature Explanation

Item terms

Bolded items

variable

Bolded

command

Italicized courier commands

command

Courier commands

prompt

Courier

response

Bolded courier fonts

23

are first-time definitions.

variable

names

in text.

are later

are

command

UNIX command

references.

system prompts. are user responses.

on which the with an example.

Italicized index entries refer to pages

or

first illustrated

UNIX command is defined

Courier

control characters like

Courier

carriage returns/enter key/return key.

Courier

escape key.

"file"

"Double quoted" items

host

'Single command All host

.

are files or directories. If taken

courier font

these will be in

'command'

definitions.

from an example,

with straight quotes.

quoted' courier commands

items are

commands

or

options in text.

names

will

be

Control characters are

in

courier font.

command sequences that means

keys simultaneously. For example, and, while holding

it

down, press the

'd' key.

use multiple keyboard press the "control" key.

HELP!

— Related Materials

XV

Book Creation A This book has been formatted with the use of L T E

X® and FrameMaker® on

A

T E X makes use of ASCII files and can be transmitted easily from one machine to another. I have made use of many different several platforms. Because L

computers (HP®,

SUN®, Apple®, and NeXT®)

sions of the book.

The book was

sty" documentstyle, called "module. sty."

command

into a

as described

file,

to write chapters for early ver-

originally constructed with a modified "book.-

in

Each of

Chapter

6.

the chapters

was included

Figures have been generated

from several sources. Most of the figures have been created on a Macintosh® and saved in PostScript form. I wrote a T E X® macro that placed a figure and figure caption into the document. This macro is described in Appendix L. On

NeXT. I can even grab portions of the screen, newer graphics have been generated on a NeXT. the

H

-

mil.ps

— /UsersAwdges/Doctinents/aasses/uy

Modo

Unix

Fie

Preface.tex

as

shown below. Many of my

•zzz:

/Doc

Control characters are command sequences which U3e multiple keyboard keys simultaneously For example, \em Cntl-dj means press the ''control'' key. and, (\em while holding it down) press the *d" key

Edit

{

*

r

r

r

\subsubsectian(Manual Creation)

•

.'

T

::

Sj

'.

i

,)i

.

manual ha een formatted entirely with the U3e of \LaTeX on a number latforms Bee ause \LaTeX makes use of ASCII files and can be transmitted achine to another. I have made use of many different ly from oj (HP. Su n. Apple Macintosh, and HeXT> to write modules for the uters al The manua s constructed with a modified 'book sty. called dule st ach of the modules is included into a command file, as Figures have been generated from a ribed in Modu .e-\ref (printing) er of sources Most of the figures have been created on a Macintosh saved in \sc PostScript) form I have written a \TeX macro which es the figur and figure caption into the document This macro is ribed in App ndix-\ref (AppC) On the (\sc NeXT). I can even grab ions of the creen. as shown on the next page, and included as I have below Many of my newer graphics have been generated on the NeXT

!

SeMcei

HMe

'

'

SO550

'

'

•

{

|

\begln(figure) [htbp| \macputhv(next eps)(28H3 00} (55) (-225) \vspace{0 05m) al preface ^ca.. in preparation ((The \figcap (next) (The \sc NeXT) and this icmai (\sc NeXT) and this manual preface in preparation \end figure)

E3

m

(

)

(

Jt-j*J.

tl.

II

itt *

»

nttai^hjkt

AhJ.jnJ.

h

ne.1

f

i

lit-:

¥ith the advent of YTeX versions running on the (\sc Macintosh) and (\sc NeXT), previewing the compiled manual and dropping figures into the files directly has made development of the manual much less painful than it was just three years ago On the \sc NeXT). an object-oriented \LaTeX development application allows the user to select environments Ouch as figure or enumer ated lists) of the document from a pallete

'

n,

then your

If

you want

to log

on

to a host

named

response will look as follows:

telnet localhost where "telnet" stands stands for the

name of the

for the

command

to connect,

and

"localhost"

host computer to which you wish to connect.

1. This discussion assumes that you have a choice of computers onto which you might log on. If you do not have a choice, then the first thing you may see is the login: prompt. If so. skip ahead to the next section. This type of prompt will likely be different at your institution.

.

O

Chapter

1 .3

Logging on to a Host

1

The Login Session

A

log-on procedure will always look the same and consists of two steps. The

host computer will prompt you for two items, one at a time: (1) your account

ID

(also

user ID, login ID. or userid) and

usually called the userid,

You must have to.

is

what the system expects

Each person using

the

computer

is

:

"

prompt.

down your account name,

called a user, and

any place

or userid. Write

that is likely to

users have a userid

all

A space has been provided, below, for you Do

or on the inside front cover of this book. here, or in

"login

at the

a valid userid and password on the computer you try to log on

that is associated with their account. to write

your password. The account ID.

(2)

it

when you receive it down your password

here

not write

be associated with your course.

Account Name:

A

sample login sequence

a host

at

shown, below, for a login session on sf suvaxl,

is

San Francisco State University.

indicating that this session

suvaxl

is

initiated

at a

terminal server prompt,

from a modem.

When I select the sfmy session to that com-

begins

It

as the desired host, the terminal server routes

puter and begins the login sequence.

sequence

called a login

is

prompt

The

thing you will see in the login

first

(login:). In this session.

I

have responded to

the "login: " request with jhodges. which is my userid on the host sf suvaxl A user' s userid is the same as their account name, and the name of their home directory. Thus, the user jhodges is the owner of the directory "jhodg.

es."

More on

this in

Chapter

3.

sfsu-annex 25: telnet sf suvaxl Trying.

.

Connected to sf suvaxl. Escape character is * A '

'

.

login: jhodges Password:

When

I

type

jhodges

at the login

ing that the system displays

my

prompt,

response as

I

my

type.

response

type will be echoed on the monitor; however, the password

you enter your prompt you will not see

for

userid, enter a carriage return

your password. Your response

your password. This

password, an encryption scheme ciated with the userid

is

it

echoed, mean-

is

that

you

not echoed. After

(), and the system will shown, so that others

will not be

a security measure.

translates

is

Most commands

Once you

and compares

it

enter your

to the

one asso-

you entered. If they match, as mine did, then you are at which point a number of things will happen, as

logged on to the machine,

I

.

Logging on to a Host

1.3

will explain next.

Below

is

I

remainder of the sample session started above:

sfsu-annex 25: telnet sfsuvaxl Trying Connected to sfsuvaxl. Escape character is Ayv .

.

'

ULTRIX V4.3

(Rev.

44)

'

.

(sfsuvaxl.sfsu.edu)

login: jhodges Password: Last login: Wed Dec 29 17:36:03 from huckleberry sfsu ULTRIX V4.3 (Rev. 44) System #32: Tue Aug 31 11:01:06 PDT 1993

(1)

.

(2)

****************************************************************************** *

* * *

for system downtime information and

Type 'news' (updated 10/20/93) for other information.

* *

*

* * *

Send your VAX questions or problem reports electronically to the email address "[email protected]".

* * *

*

****************************************************************************** Wed Jan 5 09:21:27 PST 1994 sf suvaxl> In the session above, the first line after the

from where "jhodges" at the

same

institution.

last

logged on

This means that

(at 1). I

password entry

tells

huckleberry is

when and

another host

logged on through the network. The

about the operating system version and the date. Note the statement starting "For Downtime Information. .." This block of text next line (2)

is

called a

tells

message of the day (motd). The

often send messages to

all

the users this

staff that administers a host will

way, so keep an eye on them. The

last

prompt, which signals that the login procedure has completed and I am now able to issue UNIX commands. Because you have now seen three different kinds of prompts, let's look more closely at what they mean and what you will see in the remainder of this manline

of the login procedure

is

the shell

ual.

1.3.1

The

Computer Prompts

easiest

way

application, or

to

inform the user where they are

what they should type

is

to

in the file

system, or in what

provide a visual cue.

A prompt is

a

Each utility on the computer has its own type of prompt. By recognizing the prompt displayed on the terminal screen, you can tell what utility you are in and act appropriately. So far you have seen a connect prompt, a login prompt, a password prompt, and a shell symbol(s) which performs

this function.

]

:

8

Chapter

1

The Login Session

Some

prompt.

of the different prompts that you will see are shown below.

important to remember that each prompt actions

Table

1.1:

you can

is

It is

associated with a specific range of

take.

Computer prompts

>

connect to a host

login

log on to a host

for userid

password:

log on to a

for

sfsu-annex 25:

a specialty prompt, this

&

UNIX

C-Kermit

kermit communications package

ftp>

file

$

default

Bourne

shell

Q. "8

default

C

prompt

csh>

another

localhost>

a customized is

localhost

[3

Note

— request host — request

password

one for a terminal server

mail

transfer protocol

the

shell

common C

C

prompt

shell

shell

prompt

localhost

prompt, where

name of a computer

another customized

C

shell

prompt

that the last four prompts, above, all represent different

C

shell

—

C shell prompt is the first one (i.e., the percent sign %), which is probably what many new users will receive by default. In this manual, however, examples will appear with the last two C shell prompts. There are two reasons for this. First, when you begin to log on to many hosts, it is good prompts. The stock

to

keep track of which one you are logged on

to,

and the name of the host

is

"localhost" is a placeholder for any hostname, such as huckleberry or sf suvaxl. Second, when you begin to repeat the use of commands, it is easier to do so if you remember the command sequence, and is a component of the last prompt. You will learn the sequence number 3 how to customize your shell prompt in Chapter 5. part of these prompts,

(

[

]

)

you should issue at least two commands: (l) whoami, to find out who the computer thinks you are; and (2) passwd, to change your password. Your identity on the computer can be Before ending your

checked

at

first

login session,

any time with a simple

command

called

whoami. When

issued, as

"

Changing Your Password

1.4

below, the system will respond with your user ID:

localhost> whoami jhodges

You can

command,

issue a similar

computer thinks you respond with a

are. Specifically,

to find out a little

by typing

more about who

who am

i the

computer

the will

line that looks as follows:

localhost> who am i sfsuvaxl sfsu.edu! jhodges ttyqc Jul 18 13:35

(modeml3.sfsu.edu)

.

The whoami command tells you what your userid is. This could be imporyou are wondering, later, about file or directory ownership. The 'who am i' command tells you your mail path, what device you logged on from, when you logged on. and from what port you logged on from. This can be imtant if

portant in sending mail, or for a variety of other purposes.

1.4

Changing Your Password Once logged on first is

you

to the host,

called the

will learn

.

how

cshrc to

two startup files are executed immediately. The and the second is called the login file. Later

file,

.

modify these

files to

For now, simply know that they exist called is

'"dot** files.

created and

can be

set.

and

is

you

first

because is in

in.

.

cshrc

file is

executed when your

set

.

the

first

its

commands you can you

you

is

the

created for you.

It is

issue are associated with

will issue

will see

is

commands

it

to the system.

shell

characteristics

session,

your mail path, your home directory, and other things.

the login shell that

the first thing

command

login file is executed once when you begin a login

log on to a host, a login shell all

customize your shell environment.

your home directory, and that they are

usually used to identify your terminal so that

is

Your

used to

The

in

When

called a shell specifically.

When you

prompt associated with your login

It

log

shell:

localhost>

My

localhost>. tells me what host I am logged on to. In general we will use the localhost> prompt in this manual, so that any host name will work. You can write down the name of your login host in the space prompt.

provided below and

in the

space provided on the inside cover.

1

Chapter

1

The Login Session

Local Host Name:

When you

first time, you will want to change your password you by your instructor to something unique that you will be able to remember. The reason for account passwords is to guarantee the security and privacy of your account, and you should take it seriously. You would probably not feel good if someone broke into your account and destroyed your work, or worse. Here are some guidelines for selecting passwords, all of which

from

are

log in for the

that given to

common •

sense rules to guarantee security of your account:

Never use your

when name •

Do

first

or last name: These are the

first

things

someone

will try

trying to break into your account. For that matter, avoid using any

unless you hide

it

with special characters.

not use popular or recognizable words unless modified with special char-

acters. •

•

Do

not use simple alphanumeric sequences like "aaaa."

The use of special characters and capitals is encouraged, especially when they are embedded within words that your recognize and remember. When you use numbers and special characters, place them in nonobvious locations. Avoid using numbers like zero instead of O, or 1 instead of /. These are also fairly easy to break.

•

Use many

characters: Shorter passwords are easier to break.

Many system

administrators are going to longer (8) character password lengths, so take

note of the length of the password you are initially given, because ally coincide with the

minimum

it

will usu-

length set by the system administrator.

you are generally free to select You and you alone will know your password. If you forget your password, then you will most likely not be able to access your account for some time, because you will have to inform the Other than these types of general

your

own

password.

system administrator,

Remember

this,

rules,

though:

who may then require the instructor to verify your existnew password. Going through these steps, in both di-

ence before issuing you a

rections, can take time, certainly

word

in the

first

place.

Do

more than

the effort to

remember

the pass-

not forget your password.

Only two people can change your password: someone who knows the password and someone who generates computer accounts. The system administrator generates the accounts, so he or she can modify a password. The only

who should know your password is you, which helps to guarantee no one gets into your account and causes problems. To help guarantee against accidents and snoopers, it is a good policy to change your password regularly. Many system administrators are starting to expire passwords on a

other person that

regular schedule. If you should log in and see a message like

"your

ac-

1.5

count will expire in password is

days," don't be alarmed;

6

just

As for changing your password, command, passwd:

in the allotted time.

issue a single

Logging Out

all

change your

you need do

localhost> passwd Changing password for jhodges Old password: Enter new password: Password is not different enough, unchanged. localhost> passwd Changing password for jhodges Old password: Enter new password: Verify: localhost> At

this point, the

the one

which

you

system will prompt you for the old password, which

originally logged in with,

will be echoed.

When you

is

and then the new password, neither of

have typed the carriage return

after the

new

new password by typing it a you have changed your mind, or if you enter the wrong password, then the system will act as though you never issued the passwd command at all. If you have entered the same new password, then your password is changed, and the next time you log in you should enter the new password. In the first case, above, I did not change the password enough, so nothing was

password, the system will ask you to verify the

second time.

If

done.

1.5

Logging Out When you want to terminate a login session, you to do is issue the logout command:

localhost> logout session 1 - disconnected from sfsuvaxl Connection closed by foreign host.

(

need

to log out. All

you need

130.212.010.102 )...

You can also use the exi t command to log out, particularly from remote You will now be logged off the system. If you were at a terminal or modem, then a new ">" prompt, signaling that you are again communicating with shells.

the terminal server,

would appear.

.

I

2

1.6

Chapter

1

The Login Session

Dialup Login and Terminal Servers Many

modem

people use a

connect to a computer/network. Although there

to

many advantages for logging in remotely, from home or from a business. For example, when you are home you can get up and get coffee or take a break quite easily. You do not have to come when the building or lab is open, you do not have to wait for a are clear advantages to logging in locally, there are as

on a terminal, you can probably choose the type of chair that you sit in, you can stay on as long as you can afford to. and you can (if you have a personal computer rather than a terminal) toggle what you are doing with other turn

processing tasks. These are compelling reasons for remote login that often out-

weigh the performance advantages of

you must

login,

direct login. If

you use

this

method of

your local computer with a modem and a commuknow the dialup phone numbers where you will be logcommand (if any) associated with the local terminal serv-

(1) prepare

nications package. (2)

ging

in. (3)

er. (4)

exit

know

the

connect to and log on to a host, and (5) log out from the computer and

from the terminal server. A terminal server is a special piece of hardware bank of serial lines (e.g.. from computers or modems) to a com-

that connects a

puter.

to a

to

server

many modems, and to computers and terminals.

computer and get

other computer

it is

Getting

1.6.1

A terminal

a switching station or multiplexer.

It is

connected

a terminal server prompt,

connected

to

Your Modem

is

generally

you can log on

If

you can probably log on

to

any

on which you have an account. to

Work

is not set up to help you get your modem or communications software work. Because of the plethora of modems and communications packages available, not to mention the variety of computing platforms on which they can

This manual

you in debugging your remote from a friend who has similar hardware and software, or from the business where you obtained the modem or communications software. The most common problem with getting mo-

be used, most institutions will be unable dialin.

For that you will have

dems

to

baud

rate

work

is

not having the terminal characteristics set properly, having a

mismatch, or having the communications protocol mixed up.

of these problems 1.6.2

to assist

to seek assistance

Some

are addressed in Chapter 5.

Access Numbers and Connecting to a Network

The session below puter and a

is

typical for a remote (dialup) login using a personal

modem. Once your

phone numbers available

at

instructor tells you. write

your institution below

down

com-

the dialup tele-

1.6 Dialup

baud number

(s)

2400 baud number

(s)

48 00 baud number 96 00 baud number 14400 baud number

(s)

12 00

Login and Terminal Servers

13

(s)

(s)

You can

generally create a telephone directory to store these numbers with

your communications package, and you should also write down the numbers

computer on the inside flap of this manual, as well as the characterisyou find to work for your communications package and the terminal type that works best.

for your tics

have

kermit

communications package, then you

If

you

to

precede the telephone number you use with a

are using

attention (at)

and

dial

as a

will

Hayes® command to get command will work

(dt) the telephone number. This

with any Hayes compatible

modem:

atdt3382400

The command above consists of an attention command, a dial telephone number command, a telephone number, and a carriage return, kermit and other communications packages will automatically store a telephone number list so that you do not have to remember the Hayes command set, but it is instructive to know a few commands in case something goes awry. For example, it is good to know the command for hanging up (athO) or for testing the line (athl ). Generally, a modem will come with a complete listing of its command set, and it is at least instructive to look it over. When your modem makes contact with the host location, the first response you will discern is an audible squawk (if you have a speaker turned on), and then you will see a the "CONNECT" message, such as the one shown subsequently. After you see the CONNECT response, wait a moment, and, if nothing happens, type a carriage return. The remaining portion of the message will then appear.

.

1

4

Chapter

1

The Login Session

CONNECT 2400 /REL

••••A***********************

•

* Welcome to SFSU FOGNet ***************************** *

*

!

To connect to any host,

type "telnet "

*

* *

*

To quit,

type "hangup",

"bye",

*

or "quit"

* *

*

type "?"

To get help,

*

* * *

*

To break a session, press "Shif t-Ctrl-6" and then, type "kill"

*

*

* *

*

To report modem problem,

call 415-338-1211

* *

*

*

Happy Computing!

*

*

*

********************************************************** sfsu- annex 25:

This

is

a sample

welcome message from

the network

communications

Your welcome message will probably differ, but will likely be similar. After the "Welcome to ..." line you will see a message. This is called a Message of the Day (motd). It doesn't generally change every day but can contain valuable information when it does. server here at San Francisco State University.

Every machine has the potential for showing such a message, and you should at least

glance

at

it

when you

log in to see

if

times and other messages from the person

a system administrator) will be posted to

motd

is

anything has changed. Often,

who administers the machine all

not the same as the login motd. This

nal server

and not a particular

host.

users in the motd. Note that this

motd

is

associated with the termi-

Following the motd

will

be the connect

prompt. Whenever a computer expects you to type something, vide you with a prompt of

prompt's appearance

may

some

sort.

change.

By

Depending on what you

prompt is "sf su-annex 25:." This computer you want to log on to. sion, the

this point, the user enters the host to

is

have opted to log on to the SFSU VAX

machines and what they mean

later.

should pro-

1

.

where you

8). In this ses-

will select

which

connect to and proceeds with the

login script, as in the direct login session above. I

it

are doing, the

recognizing different prompts, you can

avoid confusing problems (see "Computer prompts" on page

At

down

(called

As you can see subsequent!) the naming conventions for

More on

Notice that

I

use the

"telnet sfsu-

.

1.6 Dialup Login

vaxl"

response. This

means "connect me

and Terminal Servers

15

named

Con-

to the host

sfsuvaxl.'

sfsu-annex 25: telnet sfsuvaxl Trying Connected to sfsuvaxl. Escape character is ""* .

.

'

.

necting to a machine changes from institution to institution, and can even vary

widely within an for tor

institution. Please

how to understand on how to perform

this process,

these tasks at your institution and laboratory.

Connecting does nor mean have selected a host

use this discussion as a general guideline

and seek out assistance from your instruc-

that

and can now

you are logged

start the

in. It

login script.

typing a carriage return, the actual login procedure

See "Logging on if

you skipped

1.6.3

to a

is

simply means that you

By

selecting a host and

automatically initiated.

Host" on page 6 for more details on the login procedure

to this section.

Exiting from the Terminal Server

When you

have finished your work and logged off the host you were working you will most likely still be connected to the institution via the terminal server and will be returned to that point in the login sequence. Here you may choose to connect to another host, or you can choose to exit the terminal server by typing bye. or a suitable equivalent, as follows: on.

localhost> logout session 1 - disconnected from sfsuvaxl Connection closed by foreign host. sfsu-annex 25: bye NO CARRIER

(

130.212.010.102 )...

After you type "bye." wait until you see a

your screen

at

home

"NO CARRIER" message on

before exiting from your communications package. If you

then type "athO." locally, you will manually hang up the telephone, thereby loss. The reason is that some modems are not smart enough to know when the line has been disconnected from the terminal server, and you will end up paying the telephone company for time you weren't logged in. Alternatively, you can simply pick up the telephone receiver to guar-

guaranteeing signal

antee a disconnect.

16

Chapter

1.7

Exercises and Sample Quiz Questions

1

The Login Session

Exercises

1.7.1 Exercise

1

Log

in

and out a few times without doing anything.

Exercise 2

Change your password and

Exercise 3

Find out

Exercise 4

Successfully log in from a

1.7.2

Problem

who

log out.

the system thinks

you

modem

are.

(yours or a friend's).

Sample Quiz Questions 1

List three considerations in selecting a password.

Problem 2

When

Problem 3

List three reasons

Problem 4

What the

Problem 5

are response times the best

is

why

the difference

when logged

modem?

dial-in connections are unreliable.

between a user ID and a home directory with

same name?

You

are logged

on

to

your local host by modem. You are typing

away, having a great time when you realize

You stop to take What happened?

not working. as below.

Problem 6

in via

What

is

the difference

that

your commands are

a look and notice that the prompt looks

between the reponses

to the following

com-

mands? •

whoami

•

who am

•

What

•

How many types of prompts are

i

Problem 7 is

a computer prompt?

you

likely to see in a typical lo-

gin session? •

Show what

they look like and what utility they are associated

with.

Problem

8

Problem 9

What

are the

List the steps

two user-provided components

(prompts and responses) you will provide or see when

you change your password.

Problem 10

in the login script?

What does ATDT33812(X) mean' 1

Chapter 2 Electronic

2.1

Introduction and Most computer set

up

to serve

Communications

Scope

users have used machines set

many

up for a single user, or machines Batch mode means that an

users but in batch-type mode.

entire processing task

is

submitted to the operating system for execution,

once, instead of interactively.

Nowadays

at

a single user on an isolated systemis

commonplace, and the need to communicate with other The UNIX operating system has built-in utilities that enable you to communicate with other users on your machine. More important, these same utilities provide you access to computer users throughout the world. In this chapter you learn how to use three UNIX utilities for communicating with other computer users electronically: (1) mail, (2) talk, and (3) news. Each of these utilities is intended for specific kinds of communication and has particular standards associated with its use, called communications etiquette. When you have completed this chapter, you should be comfortable sending and receiving mail, talking with other users, and reading/posting items to a newsgroup. More specifically, you should know how to invoke each utility, how to work with it, and how to exit the utility. You should also know when it is appropriate to use one utility over another, and what factors are in-

becoming

less

users, online,

volved

and

is

less

increasing.

in effective electronic

the notion of

munications;

communication.

It is

very important that you take

computer etiquette very seriously with respect it is

as important as learning

how

to electronic

com-

to use these utilities.

17

I

O

Chapter 2 Electronic Communications

Communications Etiquette

2.1.1

As computer board.

When

find a

way

we spend much

users,

of our time in front of a monitor and key-

people are trying to reach

to

communicate through

we them, it only makes sense medium where we are most likely

us, or

the

be found. In the case of electronic communications,

most

efficient

way

communications ability to

is

communicate. The

to

communicate to

to

be the

of this potential benefit in

the potential for invasion of privacy and crank calls.

As our

electronically has improved, so has our need for a sys-

tem of communicating by adhering

flip side

this also turns out to

to

that is considerate of other users

common

on the system. Only

sense guidelines can the behavior of individuals be ac-

where you can say what you please, you do not own the network and can be restricted from access to it if you annoy enough people. As such, we will introduce some notions of network etiquette open

ceptable. Unlike the

here,

society,

hoping that you will embrace them with the sensibility on which they

and

arose,

that

you

will find

ways

to

extend them

in

your

own communications

with other users.

When you licited

send electronic mail (email) to someone, you are sending unso-

comments. You are inundating the

expense.

Of course,

a

first

reaction

your opinions

recipient with

when confronted with

this

at their

form of abuse

is

"there ought to be a law..." against this form of privacy invasion, a network etiquette that guides

and protects communication between computer

users. Well,

such a "netiquette," and it consists primarily of commonsense guideThere are different rules depending on usage, and each is touched on in book. The essence you are to glean from this discussion is that you should

there

is

lines.

this

were a communications medium, because that is what it is. When you use a shared resource, as with a networked computer, everything you do will be scrutinized by other users, and so your attitude is imuse the system as though

it

portant.

2.1.2

How to Communicate Electronically

The most prevalent problem with

electronic

communication

is

the decided lack

of inflection, facial expression, and timing that guides our understanding of

what people say. Even so, in normal conversation people constantly misinterpret comments. For example, a dry wit or a matter-of-fact statement may come off as an insult when not intended as such. When the same comments are typed at a terminal, the effect is,

ings, anger, and, often, return fire. This situation

people using electronic mail, and by the speed erated and sent.

When

or stupid, then there

is

people send mail likely to

used for electronic abuse

is

The result is hurt feelcompounded by the type of

unfortunately, exaggerated.

at

is

which responses can be gen-

that, to others,

appears unthought out

be some abuse coming back. The term often

flame.

One

of your goals as a network user should

be to avoid giving or receiving flames. There are three general rules for com-

Sending and Receiving Electronic Mail

2.2

municating your thoughts electronically:

you is

and

are kidding,

much more

(3) edit

important

(1)

be clear. (2)

1

9

someone when

tell

your messages before posting them. Being clear

when you communicate

electronically. Altogether too

often people use sarcasm and cynicism in their normal conversations. If you

when communicating

are going to use these forms of speech

electronically,

When you are joking around, the recipient may not know you well enough to understand. It is important to give them a clue as to how to interpret what you say. The most obvious approach is to say you are then you have to be careful.

joking directly, or "no offense intended.*' or something that makes the recipient that your

:-)

comments

are not intended to provoke.

:-)

can be used (sometimes parenthetically

cheek" comments. Smileys are a

comments rectly.

clear to

it

smiley face

to indicate "tongue-in-

representing

start at

A

humorous comments, or

have double meaning that you want the receiver to interpret cor-

that

As you Use them carefully. Avoiding what you write. Read the message over

Their use can be abused as easily as any form of communication.

will learn, there are

many ways

to type a smiley.

flames can only be achieved by editing

again after you have written your reply. Think of

all

the recipients to the

mes-

sage and the ways they might interpret your response.

2.2

Sending and Receiving Electronic Mail UNIX

has a built-in

command,

called mail, for sending messages to and re-

ceiving messages from other users.

You

will find this to

communicate with the course assistants or instructor as well as to friends.

for all intents

Although your use of email

be an effective way to

when you have

questions.

will be limited to begin with,

is no difference between sending mail to Germany. Sending a message to someone re-

and purposes there

someone across

the

room

or to

quires five types of information.

•

How How

to

•

How

to address the mail

•

How

to

•

How

to receive

•

The is

first

to use

invoke and exit the mailer

compose

item

required for

email appropriately

all

is

the

message

and manipulate messages

addressed by looking

at

email netiquette. The second item

applications and should be the

first

thing you

try,

such as log-

ging in and out of the computer. The third item introduces the notion of mail

path or address. The fourth and

fifth

items introduce the mailer(s) and their

use.

2.2.1

Netiquette and Email

Before you learn

how

to use email, there are a

using email that you should alw ays keep

in

few guidelines

to follow

mind. The essential notion

when

in every

20

Chapter 2 Electronic Communications

one of these rules

is

think first. If

you do

this

one thing, then you will enjoy

using mail without becoming frustrated or frustrating someone else. •

Never send a piece of mail to anyone who doesn't know who you are. This means that YOU are responsible for checking the carbon-copy (cc) list on incoming mail

to

make

sure that

you do not

proliferate

your response to the

entire free world. •

Never send out any sort of solicitation. shows extremely poor taste.

•

Think before you respond. Perhaps you should compose all your responses in separate files and edit them before putting them into a mailer.

•

When

It is

an invasion of privacy, and

it

using electronic mail, always identify yourself and leave a return

email address. The most appropriate location for the return path

message,

at the

end of your message. That way, when someone

is

is in

your

done read-

ing your mail, they have your return path looking at them in the face. •

Learn what a smiley face

work way of saying

(just

ley faces, e.g., tongue in

is

and do not abuse

kidding

cheek

:

-

)

A :

)

,

.

its

use.

A

smiley face

is

a net-

There are probably hundreds of smi-

oh-no

:

-0, sad-face

:

-

(

,

etc.

•

Never "flame" someone. If you must clarify something sent in email, then think about what you are saying, how you are saying it, and why you are say-

•

Never do anything

ing

son

it.

Don't send mail just

who

that

to toot

your

own

horn.

might draw the attention of the postmaster

sending mail to your postmaster about you, then something

As you can

(the per-

administers mail on the computer). If users from other locations are

see,

is

very wrong.

email netiquette does not place unreasonable restrictions

on what you send. Rather,

it is

intended to

make

sure that users are considerate

of one another.

2.2.2

Electronic Mail Addresses

Sending a message to someone requires an address to send the mail

to.

With

you need a name, an address, and a zipcode. With a telephone you need a telephone number. With email, the situation is similar, except that you use the userid instead of the name. The address can be replaced with the symbolic machine address where the user's account is located. The machine address is associated with a uniquely numbered sequence called an Internet Protocol (IP) address. A machine's IP address is usually associated with one the postal service

more symbolic names. The machine's IP address can also be used to address mail, similar to a zipcode or telephone number. If you know a person's userid and machine address (symbolic or IP number), then you can send someone mail. For example, the entire symbolic address for the host sf suvaxl looks or

as follows:

sf suvaxl sf su edu .

.

.

2.2

In this example, both

Sending and Receiving Electronic Mail

sf suvaxl and "sf suvaxl sf su. edu" .

chine address. Actually, both are aliases for the real ically reside in a file

named "/etc/hosts" on most machine address

IP-address symbolic-address namel name2

An example

is

.

are the

ma-

machine address, and typ-

hosts, you

will find

21

systems. In

/etc/

entries of the form:

.

shown below:

localhost> more /etc/hosts

# #

Host Database

#

130.212.10.102 sfsuvaxl.sfsu.edu sfsuvaxl vaxl 127.0.0.1 localhost

The lines starting with pound signs (#) are comments. The first non commented item (i.e., 130.212.10.102) refers to the machine's Internet Protocol (IP) address. The IP address comprises four numbers separated by periods. The IP address can always be used in internetwork communications. The next entry refers to the machine's symbolic name address (i.e., sfsuvaxl sfsu. edu), and all additional columns refer to pseudonames, or aliases for the machine address. Thus, 130.212.10.102, sfsuvaxl sf su edu. sfsuvaxl. and vaxl all refer to the same computer. The difference between them is that the IP address is recognizable by any machine on the network, the symbolic address is recognizable by most machines on the network, and the aliases are only used locally. .

.

.

A space has been provided, below, for you to write down your host's symnames and IP address. You should manual for quicker access later.

bolic this

also write

them on the

inside cover of

Localhost Symbolic Names: IP Address

The name address follows

a convention, as follows:

HOST INSTITUTION INSTITUTION-TYPE .

.

The name (symbolic) address

for

sfsuvaxl

in the

/etc/hosts

file

c.2.

Chapter 2 Electronic Communications

above

tells

and the

"HOST"

us that the

sf suvaxl,

is

"INSTITUTION-TYPE"

tution types are

commonly

mai l

Table 2.1:

is

edu.

the

edu,

is

Institution types

Commercial organizations

.EDU

Educational organizations

.GOV

Government organizations

.MIL

Military organizations

.NET

Network organizations

.ORG

Other organizations

.UUCP

Dialup connections

institution-type can also be a country-code, if the host

is

outside the

United States. For example, the institution-type for hosts in Canada Brittain is

How

.UK, and Australia

does

all this

sf su,

six other insti-

used:

.COM

The

"INSTITUTION"

In addition to

is

is

.CA,

.AU.

Remember, if you you can send them mail. The

address stuff affect electronic mail?

have a user's userid and

their mail address, then

standard notation for mail address

is:

name&domain where "name"

"domain"

is

is

a person's userid, "@" separates the

their

mail address. The mail address

address where the account then

it it is

message

is

located. If

is

interpreted as the

name of

is

domain does

name and domain, and identical to the

domain. For example,

(.),

the local (current) host. Otherwise, the

passed to a mail host (name server) that determines

the specified

machine

not contain any dots

if

your account

is

how

to get to

on the machine sfsu-

vaxl and you want to send the user jhodges some mail, then you could use the userid alone, as follows:

jhodges

If,

conversely, you wanted to send mail to John Q. Smith

whose account ify the entire

is

on the host

mail address.

JSMACHINE, you would

at

Podunk University,

probably have to spec-

Using the UNIX mail

2.3

j

23

Utility

qsmi th@ j smachine podunku edu .

.

"jqsmith" is the userid, HOST.INSTITUTION.INSTITUTION-TYPE the machine name " j smachine" is the host, the school

where, according to the template provided above,

and the domain breaks down as before. In this case,

"podunku"

is

to

the institution, and because John Smith's account

cational institution, the institution-type particular system

mail address

2.3

is

is

In this section, the

unique, and because the machine address

an edu-

is

unique, your

Utility

methodology and

UNIX mailer, /usr /ucb/mail is

is at

"edu." Because every userid on a

unique.

Using the UNIX mail

mailer

is

presented.

Many

is

essential

commands

for the standard

presented, and. in the next section the

other mailers are available, such as

MH

Emacs mail.

elm, pine, and mush; however, they are similar in use to one of the mailers You should try them if the ones presented here are insufficient

discussed here. for your needs.

mail mail

is

is

the standard, out of the crate.

UNIX electronic

mail

utility.

Your

generally directed to a home-level directory and then accessed by what-

mail is fast and accessible, but not altogether user common commands used are given below, but a full de-

ever mail handler you use. friendly.

Some

of the

found using the manual pages (type 'man mail' command). What characterizes UNIX mail is its environment. When you invoke mail, alone, your prompt will change from whatever it was to the folscription of the mailer can be

as a

lowing:

see this prompt, you are in the mail environment, so do UNIX commands. The easiest way to get out of mail, without

Whenever you not try to execute

changing anything,

&

is

to type the letter 'q' as follows:

q

Writing and Sending a Message

2.3.1

Using mail to.

1.

so

all

is

easy.

You

you need now

Also known as a mailer or mail handler

already

is

know

something

that

you need an address to send the mail The mail utility provides you with

to send.

:

.

24

Chapter 2 Electronic Communications

several

A

it.

mechanisms

for writing

simple example

and manipulating the message before sending below, and a list of commands follows so

illustrated

is

you can experiment with mail on your own. The easiest form of email is someone who has an account on the same machine as you. In this case, you need only know their account name. Suppose the person you wish to send mail that to

John Q. Smith, who has the userid jqsmith. To send your friend Smith a message using the standard UNIX mail utility you would enter the command to is

as follows:

localhost> mail jqsmith

the

computer

respond with

will

Subject which you enter a one-line subject of your message, for example:

to

Subject: Party this Saturday.

.

.you're invited!

The computer will move the cursor to the next line and wait for you to enter the body (content) of your message. You enter your message one line at a time, separated by carriage returns. At this point, you will not be able to edit your message other than to back space over incorrectly typed text. That is, you will not be able to move up a line and change a spelling. If you want the ability to edit your mail completely, and you know how to use an editor, then you can use your editor from within the standard

vided here, for the

vi

editor, but a

mai 1

utility.

A brief overview is pro-

complete discussion of

sented in Chapter 4. In your message, on a blank

line,

editing

file

is

pre-

type the following (tilde-

v):

-v

and the default editor itor is

will

invoked, you can

character, with the

'

be invoked on the your message body.

move

j,' 'k,' 'h,'

and

'1'

keys on the keyboard.

You can char,' where char is the new

characters directly under the cursor using the 'x' key. acter under the cursor with 'r

can return to the mailer by typing two capital Zs.

you can continue writing

1

message where you

See Chapter 4 for information on how to invoke and use an

the default editor in 2.

the

See Appendix

G

editor,

the ed-

When you left off,

You can

vi and related commands.

delete

replace a charcharacter.

are

done

You

editing.

or you can send the

and Chapter 5 on how to

your mailer. for a short description of

Once

the cursor around the message, character by

set

2.3

Using the UNIX mail

25

Utility

When you have completed entering your message, type either or a period (.) on a line by itself. The mailer will respond with:

message.

a

Cc:

which means carbon copy. yourself),

sending a message, type

An

you want

to

send the mail to anyone else

their userid's here, separated

list

carriage return key ().

Other Ways

2.3.2

If

alternative for

The message

to

by commas. Otherwise, press the

will automatically be sent.

(twice) before sending

To

abort

it.

Send Mail

composing mail involves editing a

mailer and then sending

(e.g.,

it.

Two

before invoking the

file

approaches are presented here, both of which

assume that you have already composed the message with your favorite editor and named it "mesgl." In the first case, you will include a file into the body of the mail message. First you enter the mailer normally

(i.e.,

with the

command). When you get to the point where you would normally the message text, type the following (tilde-r) on a blank line:

start

mail typing

-r mesgl

at

which point

the mailer will grab the

file,

stuff

segments into a mail message the

vi

this

way, you can copy

easily. Tilde-r is similar to the

editor (see Chapter 4), both of

merging

into the current message,

it

and return you to typing mode for the message. In

which have

the

same

' :

r'

file

command

in

effect of including/

files.

A second way to incorporate "mesgl" into a message is to use redirection (see Chapter 5, page 157). For the sake of continuity, the here. All

you need

localhost> mail jqsmith


mail -s "subject" jqsmith where the

mail

message subject

line




The new

you have no new mail, but have mail that hasn't been removed (or read) from you mailbox, then you will receive this message without the [new] part. If you have new mail, then you will receive this message without the brackets. In either case, to receive mail, part

merely enter the

is

bracketed here for a reason.

mail command

If

alone:

localhost> mail

If

you have new or unread mail, then

a

list

played according to the format below:

[STATUS] [NUMBER] [USERID] [DATE] [SIZE] [SUBJECT] where each

Table 2.2:

classification

mail Message

list

is

described below:

information

STATUS

(N)ew

NUMBER

The mail

USERID

The

userid (or mail alias)

DATE

The

date the mail

SIZE

The message

SUBJECT

The

mail, (U)nread mail, (D)eleted mail

first

identification

number

who

sent the mail

was received by

the mailer

size in lines/bytes

few characters of the subject

line

of the messages will be dis-

2.3

Using

this format,

Using the UNIX mail

consider the sample listing of messages

27

Utility

shown below:

localhost> mail Type ? for help. Mail version 5.3 2/18/88. /usr/spool/mail/hodges " 92 messages 11 new 48 unread 81 [email protected]. ED Sat Jul 13 16:02 43/1625 "NeXT Campus Consul" Mon Jul 15 07:18 47/1937 "intrusion into my" >N 82 [email protected] Mon Jul 15 09:38 12/350 "Re: Leave of Absence" N 83 eisman "Re: address" Mon Jul 15 09:40 14/408 N 84 eisman Mon Jul 15 09:41 12/350 "Re: Huckleberry upgr" N 85 eisman "Re: CSc 214" Mon Jul 15 09:45 13/426 N 86 eisman 61/2105 "NeXT" N 87 [email protected]. ED Mon Jul 15 13:25 "last message" 18/794 N 88 [email protected]. ED Mon Jul 15 13:27 Mon Jul 15 15:36 29/951 "Re: Allegro Goodies N 89 barbara Mon Jul 22 16:18 15/573 "Postscript graphs fo" N 90 phoebe Mon Jul 22 22:07 37/1451 N 91 [email protected] Tue Jul 23 12:55 13/339 "test" N 92 barbara "

(l)

:

"

@

&

Notice that the

first

thing you will see in the listing, other than the version

number and help message,

is a header (at 1) telling what your mail path is, where your mail is stored locally, how many messages are stored there, and what their general status is. The mail path in this display is /usr / spool /mail/hodges. which describes a directory in the UNIX file sys-

which

is

tem. There are 92 messages in the mailbox,

which have not been tion

1 1

of which are new, and 48 of

read. Thus, the listing that followed only displayed a por-

(messages 81 to 92) of

all

the mail for the user hodges on this machine.

Each of the remaining lines describes a specific mail message. The "N's" column mean that these are new messages. Message 81 has no status character, meaning it has been read. The greater than symbol (>) next to message 82 indicates this as the current message pointer, meaning that this is where you are "located" in the list. in the "status*' (first)

If a userid is alone, in the third (userid)

sides

column, then the user account

on the same host or subnet where the mail was received, as

in the

re-

case of

"eisman," "barbara," and "phoebe." When a user is on the network, the userid and symbolic mail address is used, as in "vo j in@omen SFSU EDU." .

The next four

fields

.

(columns) identify the day and time (on a 24-hour

was received. For example, message number 91 was reat 10:07 p.m. The next field for message 91 indicates the size of the message, which, in this case was 3 7 lines and 14 51 bytes. Notice that message 91 has no subject line. Finally, notice that when the display is complete, you are now in the mail environment, because the prompt has changed to an ampersand (&).

clock) that the mail

cieved on Monday, July 22,

Suppose

that

you want

to read

one of these messages. All you need

to

do

Ao

Chapter 2 Electronic Communications

is

type the mail ID number. For example,

89, so

& 89

I

I

decided to read message number

typed the following.

Message 89: From barbara Mon Jul 15 15:36:53 1991 Return-Path: Received: by toaster.SFSU.EDU (NeXT-1.0 (From Sendmail id AA28412; Mon, 15 Jul 91 15:36:51 PDT From: barbara (Barbara Ford) Message- Id: Subject: Re: Allegro Goodies from Franz Inc. To: [email protected] (John Hodges) Date: Mon, 15 Jul 91 15:36:50 PDT In-Reply-To: X-Mailer: ELM [version 2.3 PL10]

5

.

52

)

/NeXT-1

.

)

(T)

.

.

.

Status: R > Barbara, >

At the same time we ordered the Franz upgrade we ordered some software upgrades for the FrameMaker application (wordprocessing and page > layout) Could you possibly check and see what happened to those orders > for me? > >

.

>

Thanks a lot.

>

Jack called New York Frame Technology and the upgrades for Frame Maker 3.0 for both the Macintosh and the IBM will be shipped out this week. I think that does it? Does it not?

> I

&

There plate

is

a lot of information in a mail message! Let's take a look at a tem-

mail header and then you will be able

fused, by the preceding example.

to appreciate, rather than

be con-

:

Using the UNIX mail

2.3

Table 2.3:

Utility

29

mail Message header information

Message 89:

The mail message number

From

The userid who

Return-Path:

The

Received:

The host

From:

The

Message-Id:

The host

Subject:

The mail message

subject line

To:

The mail message

recipient

Date:

The

date the message

In -Reply -To:

The

originating

X-Mailer:

The mailer used

Status

The

This

is

sent the

userid to which a reply should be sent that received the

message

userid and mail alias (from finger file) identification

number

was

status of the

to

message

sent

compose

the

line

message

message from the originating sender

a complete header.

that are offset

for the

message subject

When you read mail you may

header. Notice that the message

ments

message

body accompanying

by greater than signs

(>).

This

not see a complete

the header includes is

com-

a standard protocol for

reminding a person of the original context of a mail message, so that the reader doesn't wonder what the sender

is

talking about.

You can

type these directly,

or you can learn to automate the process.

In the example message above, the message easily fit into a single screen. Had the message been too long to fit, it would have scrolled past. To look at it more leisurely, you can do one of two things. First, you can specify how many lines are displayed before a display "pager" is invoked. This is accomplished with the crt variable in a file named

.mailrc" that resides in your home directory. You may not have such when you receive your account, but you can create one as long as you are ful. A value of 25 will work for most terminal screens. "

1.

You can do

this

by writing a

script

and piping mail messages through

Script writing and. in particular, a script that performs this type of task,

it

is

before they are sent.

covered

in

Chapter

13.

a file care-

OU

Chapter 2 Electronic Communications

set crt = 25

you may save the message

Alternatively,

to a file with the mail 's'

com-

mand: & s

#N

f ilenarae

where "s" stands

"filename"

is

the

for save,

omit the #N, the current message

#N1-#N2. You may

at

file

is

you want

to send the

message

to. If

you

You can also use a message range, the 'q' command and read the file us-

saved.

then quit mail with

ing your favorite editor or use the

The mailer

"#N" stands for the message number, and

name of a new

more

paging

utility.

20 messages at a time, so if you want to look messages displayed, you need to issue the fol-

will only display

messages before or

after the

lowing command: &

f

N1-N2

where "f " means to take the message list lines for the following message number range and display them, "Nl" is the range starting message number, and "N2"

is

Responding

2.3.4

To respond &

the range ending

to

message number.

Email

message, type the following mail command:

to a

R #N

where "R" stands

for reply

and "#N" stands for the message number

you are responding. The mail address of the appear

in the correct location, the subject

then you will be given the opportunity to

is

to you, but they

possible that

compose your message.

will

is

you

intentionally. Generally,

arc doing >

it

tricky. If

to

someone has

many

to the particular

person

who

sent

sent a mes-

other users, then

it

send your response to the other us-

called implicit carbon-copying. This

ers as well. This

sponse

original sender will automatically

have sent the same message

when you respond you

which

of the message will be repeated, and

Replying to messages can sometimes be e

to

is all

right as long as

however, you should send your

you mail

in the first place. If

re-

you use

the "r" instead of "R" your response will be sent to all the original recipients

of the message. users are

li^

In general,

you should look carefully

to

make

sure that no other

J as recipients before using "r" to reply to mail.

Using the UNIX mail

2.3

Forget Those Long Mail Addresses

2.3.5

possible to create a personal distribution

It is

list,

-

Utility

31

Mail Aliases

or

list

of aliases, so that you

can send mail to a group of people without using their userid and mail address.

Such

lists

can be defined by placing a

your home directory

in

(if

one

following in the .mailrc

line like the

file

exists):

alias alias-name addressl, address2 ... who work

For example, suppose you have three friends

at different busi-

nesses but you get together occasionally or share funny stories online. Instead

of retyping their addresses called

the time,

all

you might want

to create a mail alias

"cohorts:"

alias cohorts bills@widgetsrus .com, larryw@f tn500 com, sue .

where "bills." "larryw." and "sue" are your friend's userids on their local hosts, followed by their mail addresses to which a message addressed to "co-

horts" will be sent. To display the current list of such aliases, use (a) command from within mail. Systemwide distribution lists "bugs" and "help." where they

exist) are defined in

the alias

(such as

lib/alias-

"/usr/

es." Contact the system administrator to be added to a systemwide mailing alias.

Forwarding Email

2.3.6

some circumstances,

In

a user

to

Other Users

may have

multiple accounts on a machine, or ac-

counts on multiple machines. In such cases,

shown subsequently. Be

done, as

ily

which might be redirected back

nice

it is

to read mail sent to an account, or to forward

it

if

you can decide whether This

to another account.

is

eas-

careful not to produce any forwarding

to the original account, as this is called a cir-

cular reference, and will cause problems for your local postmaster. The for-

mat

for producing a mail forward

your home directory. is

be

to

file

In this file,

is

you

to create a file

named

.

insert a line that specifies

For example, consider the example below, which

sent.

forward"

"

in

where the mail

is

a

.

forward

from the host sf suvaxl:

localhost> cat .forward hodges@ futon. sf su edu .

In this

.

forward

mail receiving account)

sf su edu. The .

file, is

mail that

is

sent to

jhodgesdsf suvaxl (the futon -

forwarded to the user hodges on the host

nice thing about forward files

is

that

.

you can selectively de-

cide whether to forward or not, depending on the machine and the type of traf-

32

Chapter 2 Electronic Communications

you receive from the machine. Also, if you edit your forward files in all accounts except one to include to remaining account, then you need only log fie

.

into that (remaining) account to receive all of careful,

when

creating

.

forward

files

wrong person,

sent to your userid will either be sent to the

returned as unsent to the user

A

who

sent

You must

your mail.

be very

not to type errors, because mail then

it.

This

is

or,

worse,

it

will be

called mail bouncing.

to forward mail is when you you leave town for some reason. In such cases, you may want people sending you mail to receive a message informing them that you are unable to respond for a while, to tell them how to

second occasion

in

which you might want

are unable to respond to mail for a period, e.g., if

vacation utility is supported on your host, you can modify forward file to use the vacation utility as shown below. To use the vautility, you must first initialize it before you change your forward

reach you.

your

.

cation

If the

.

file:

localhost> vacation -I

This will add two directory,

and ".vacation. pag" to your home

files: ". vacation. dir"

vacation

will not

modify your ".forward"

file as

work unless you have done shown below:

this.

Now

you can

localhost> cat .forward hodges, "| vacation hodges"

This

is

a different kind of

.

forward

than the previous one, to

other feature, that of sending yourself mail

(hodges) makes

at

show

multiple hosts. In this

file,

anthe

you receive a copy of the mail sent. The second item pipes the received mail into the vacation program for the user hodges. Piping does for commands what redirection does for files, by elimiitem

first

nating the need to display a put). Instead the

When you fined in a

file

\

command's output

response from one

"

n subsequently.

.

is

sent a

vacation. msg." to

to the

monitor (or standard out-

command becomes

are sent mail, the sender

named

The message you send sin

sure that

the input to the next.

message whose content

residing in your

home

is

de-

directory.

people should include a mail header for them, as

2.3

Using the UNIX mail

Utility

33

localhost> cat vacation. msg From: [email protected] (Jack Hodges) Subject: I am showing an example of a vacation message Delivered-by The Vacation Program Please bear with me, I am showing an example of the UNIX vacation program, and will turn this off promptly .

:

J. B .Hodges

2.3.7

Table 2.4:

Internal

mail Commands

mail commands

-

Display the previous message

?

Display a brief summary of

i

Execute the

(R)eply

Reply

to originator of

(r)eply

Reply

to

With no arguments, display all currently defined aliases. With arguments defines an alias called name for addresses

(a)

lias name list

in

(c)hdir DIR

(co)py N1-N2 FILE

command

sender and

that follows

message only

all

original recipients

list

Change your working

directory to

Append each message do not mark

(d)elete N1-N2

shell

commands

the

in list

DIR

N1-N2

to

filename FILE, but

messages for deletion

N1-N2

Mark

Delete the current message, and display the next one

(ex) it or x

Return to the shell immediately, without modifying your mailbox

folders

List the

(fo)lder

Switch to a new mail

(f)rom N1-N2

Display the message headers for the message

(h)eaders

List the current range of headers; an

dp

the

message

names of

list

as deleted

folders in your mail folder directory file

or folder list

Nl -N2

18-message group

34

Chapter 2 Electronic Communications

Table 2.4:

Internal

mail commands

(cont)

(m)ail list

Send mail

(n)ext

Display the next message in the sequence

(p)rint N1-N2

Display each message in the

(q)uit

Terminate the session, saving

(s)ave N1-N2 FILE

Append each message in list N1-N2 mark each message for deletion

to users specified in

Each of these can be typed out

minimum

in full.

list

list

all

N1-N2 on

undeleted messages to filename

FILE, and

The parentheses simply

characters that have to be typed for the

any others included are optional for the

the screen

command

to

indicate the

be recognized;

user.

I have mentioned several tilde (~) commands, ones that are used while composing a message, specifically for editing a mail message and including external files into a mail message. Below are a few additional tilde commands for mail, but this is not an exhaustive list. Remember that each of these commands must be issued on an empty line.

Table 2.5:

Internal

mail

tilde

commands UNIX command COM

-!COM

Execute the

~b USERS

Blind carbon-copy the message to userids

-C USERS

Carbon-copy the message

~f N1-N2

Read

~m N1-N2

Same

-r FILE

Read contents of FILE

-t USERS

Send the message

~v

Edit the message with the editor defined by the .mailrc

~w FILE

Write the message

-COM

Pipe the message through

--STR

Insert the string

the messages in as

~f

to userids in

N1-N2

into this

in

USERS

USERS message

but tabs are included into the

message

to the userids in

to

STR

filename

USERS

FILE

command

in the

EDITOR

as a filter

message, preceded by ~

variable in

.

2.4

MH — The RAND

— The RAND Mail Handler

MH

2.4

35

Mail Handler

MH is a mailer developed by the RAND Corporation to run in the UNIX command shell. Unlike the UNIX mail handler "/usr/ucb/mail," MH is more transparent to the user using UNIX commands. MH is not a single program that is invoked with a single command, like mail. MH consists of a package of programs

that are

executed individually rather than collectively as a separate

process. Output from

MH commands

is

normally displayed on the screen, but

UNIX processes, and output from other UNIX process-

can be piped into other

MH commands. This way the user can intermix mail reading/responding with other UNIX processing activities quite easily. The MH en-

es can be piped into

vironment can be used as ".mh_profile that

,,

file in

is

but can also be customized by creating/editing the

your home directory. This

created the

file is

first

time

you invoke MH.

Up the MH Environment to use MH you must invoke one of its utility commands to initial-

Setting

2.4.1

Unlike mail,

One way to do this is to send yourself mail and incorporate it with the command, inc. Another way is to compose a mail message with the MH command, comp. The initialization will be demonstrated with the former apize

it.

MH

dummy piece of Now you are pre-

proach. If you do not have any unread mail, send yourself a

mail with the subject line

pared to

initialize

MH

"testmail" and

with the inc

don't read

command. Type

it.

the following at the shell

prompt:

localhost> inc I'm going to create the standard MH path for you. Create folder /usr/f 1/ jhodges/Mail/inbox" ? y Incorporating new mail into inbox. 1+ 01/28 To:jhodges testmail "

(7)

.

(T)

MH will now create a ".mh_profile" file, and

it

will ask

you

if

you want the

name "Mail," (at item 1). When you respond, MH will continue by incorporating new mail into your local mail folder (called "inbox") as shown at item (2), whereupon you can use MH to process mail. The " + " in this listing means that message is the current message, or the one standard mail directory

1

which

will

Now, be

be displayed

if

if

the user types

you wish, you can

edit

similar to (or exactly like) the

show

without a message argument.

your newly-created

sample

file

provided.

commands noted in the next section. If you want more the man entry for MH (i.e., man mh).

" .

mh_prof ile"

You can

then use

to

MH

information, please read

36

Chapter 2 Electronic Communications

Table 2.6:

Components

of the

MH

.mh_profile

Path

Mail

directory for mail folders

Draft-Folder

drafts

directory for drafts

prompter-next

prompter

prompt

Editor

vi

default editor

Msg-Protect

600

permissions on

new

articles

Folder-Protect

700

permissions on

new

folders

Signature

Jack Hodges

user signature for messages

anno

-inplace

directory for mail folders

dist

-annotate -inplace

form

forw

-annotate -inplace

form for forwarding

send

-verbose -alias aliases

where

scan

-form scan. size

what

to

do with

inc

-form scan. size

what

to

do with incorporated messages

ali

-alias aliases

where

to find aliases

whom

-alias aliases

where

to find legal mail addresses

2.4.2

Below

for editor to use

for distribution lists lists

to look for mail recipients

the scan

command

MH Commands is

a

list

of useful

MH. Some of these

MH commands.

aren't

These are commands

to

needed often, but have been included so

be used with that

you can

by quite nicely with comp, send, repl, forw, inc, next, scan, show, prev, refile, folder, and rmm.

experiment with them.

You can

get

2.4

Table 2.7:

MH

— The RAND Mail Handler

MH commands

ali

list

anno

annotate messages

comp

compose

dist

redistribute a

folder

scan +mine

which

will display a standard

folders with the

the

MH mail message

list.

folders command and change

Note

you can

that

list

mail

the current mail folder with

folder command.

The

2.4.3

You can add

MH

Aliases File

a personal alias

your "Mail"

file to

the complete mail addresses of people that

remember

not wish to

The format

their address.

director}'.

This

file

you routinely send mail is

contains to but

do

shown below:

localhost> cat -/Mail/aliases class chong,manrson, adrey, goss, grenf eld, gog, chi whir ten, gudermon bunns mike dwyerOcs ucba edu test: hodges wienrab:wienrab%oso-70@ohio-state arpa everyone * ralph hyper@hqlabs hq com, hyper%hqlem@hqlabs HQ COM tedc IGRQTGCOOC UCBA EDU ,

:

,

:

.

.

.

:

.

:

:

.

.

.

.

.

The "aliases"

file is

organized by alias names, such as class. The items

in the alias entry are listed,

each separated by commas, and offset from the

name by

alias entry is

a colon

location in

without

use

full

:

).

The

comp. Note

full

those with

(

the variety of e-mail addresses in this sampling.

paths are IDs local on the host where the alias

full

paths will

work from any

alias

used by typing the name into the To:

host. In general,

mail paths in case you copy/move

it

to

your

another host.

Those

resides, whereas alias file

should

:

2.4

— The RAND Mail Handler

Composing a Message Using

2.4.4

A sample

39

MH

MH to write and send a message is shown below. Supcompose a message to someone. The MH command to

session using

pose that you want to use

MH

comp. When we type comp, depending on what editor has been selected will get an edit window for the purpose of writing the letter. In example, the vi editor is used, so the comp window will look as follows:

is

by the user, we this

localhost> comp To: CC :

Subject

space reduced for readability

"

/usr/f 1/ jhodges/Mail/draf ts/43

"

26 characters

lines,

4

This example normally takes up the entire screen. size here to save space. In this case,

It

has been reduced

you would use vi commands

in

to insert the

mail address for the recipient, the subject line, and the content of the message.

An example

is provided. To insert the recipient's mail address, you could type a '$' to get to the end of the "To" line. This would place the cursor on the co-

You

'a' to append text, and then type the address after which you would press the key to stop appending. To move down to the subject line, you could type a j twice, one for each line. Then you could use the same procedure as for the mail address (i.e., $, a, type text. ) to type the subject, again finishing by pressing the key. You would then type a j to get onto the line of hyphens, and an 'o' to type the text of the message. When you are done composing the message, you type an key again, and you exit comp by typing the standard escape key for the editor you are using. In vi. you would type ZZ. At this point you will see the following (what now?) message:

lon.

could then type an

the colon, after

'

'

'

'

What now? h -h unknown. Hit for help.

Normally you respond with something

quit.

In this example,

tions to

I

makes

sense, like

mistyped and then took the opportunity

"What now?" When

the mail.

that

I

was done

I

used the

send

or

to list the op-

send command

to

send

40

Chapter 2 Electronic Communications

What now? Options are: display [] edit [ ; list [] push [] quit [-delete] refile [] +folder send [] whom [] What now? send

Two items of note are the "What Now? Options" Normally when you want

to post a mail

and the drafts

folder.

message or news posting you would

send, but you may also wish to review the original message using display, edit the file using edit, refile the message to a folder for future use with refile, and so on. The "drafts" folder holds copies of all mesreply with

sages you have composed, for future reference.

2.5

Problems Replying to Email You

should be able to give people

at

other institutions your email address and

when you try to send somemail will bounce (be returned un-

they should be able to send you mail. Sometimes

one mail, or they

try to

send you mail, the

sent).

There are different reasons for bounced mail, two

which

will be introduced here: unavailable service,

common

ones of

and address problems. The

bounced mail may not be your fault; if you find that you have the same problem repeatedly, you should speak with the postmaster or bottom

line

is

that

system administrator. 2.5.1

Returned Email: Service Unavailable

Occasionally systems crash. Should you be sending or receiving mail

when

a

crash occurs, your mail should be kept in a mail spool directory on the mail

gateway site,

and

until the its

system

is

restored.

Should you be sending mail

to another

network crashes, then you may have your mail bounced and

ceive a cryptic message, such as the one

shown subsequently.

re-

)

2.5

Problems Replying

41

to Email

>From MAILER-D%ucsbuxa@hub ucsb edu Mon Jan 30 14:09:10 1989 Return-Path Received: from hub.ucsb.edu (hub.ucsb.edu. ARPA) by corwyn.cognet.ucla.edu (4.12/1.3) .

.

:

.

.

id AA06823; Mon, 30 Jan 89 14:09:01 pst Received: from ucsbuxa.ucsb. eduby hub.ucsb.edu 5 59/UCSB-v2 id AA18004; Mon, 30 Jan 89 14:06:25 PST Received: from hub.ucsb.edu by ucsbuxa.ucsb.edu (3 2/SMI-3 2 id AB13170; Mon, 30 Jan 89 14:07:58 PST Date: Mon, 30 Jan 89 14:07:58 PST From: MAILER-D%ucsbuxa@hub. ucsb. edu (Mail Delivery Subsystem) -« Subject: Returned mail: Service unavailable ~« Message-Id: To: (

)

.

.

.

.

The message in

at

item

(1), the

subject line, tells you that there

sending the mail. The message

work

related.

down when for a certain

note like

it

item (2)

tells

you

that the

was

a problem

problem

is

net-

This message bounced because the remote host/system was received the mail. Normally, attempts to deliver mail are

amount of time

this,

at

(say 3 days) before bouncing. If

made

you should get

chances are reasonable that resending the message

at

a

another

time will succeed. Otherwise you should notify the postmaster. 2.5.2

Email Address Problems

There are two

name

common

mail address problems everyone should be aware

of:

Sometimes you will receive mail and find that you cannot reply without receiving a bounced message. This may be caused by a mail server that cannot find your address (at their end), their address (at your end), or some combination in between. If this is the case, then you may be able to succeed by changing the intended recipient's mail address, on your mail, to include a machine that is very likely known. You then (1)

server problems and (2) uucp addresses.

let that institution's

name

server figure

it

out. In

such cases, apply the follow-

ing rule:

replace the first @-sign with a %-sign and tack on ©domain at the end where domain is your local machine address. This will route your mail through known machine before sending it out and usually fixes problems in mailer

a

confusion.

42

Chapter 2 Electronic Communications

Here

is

an example of a modified mail address:

jqsmith% jsmachine .podunku. edu@sf suvaxl sf su. edu .

UUCP Mail

2.5.3

UNIX

UNIX

to

bounced

System Copy (uucp) addresses are another primary source of Mail addresses that end with the UUCP Institution-type, such as

mail.

the one below:

.

.

.

[host

!

]

host username !

are

sometimes mistakenly referred

provides links to numerous

sites

to as

of files (see anonymous ftp, Chapter a network connection and

usenet or internet addresses,

7,

page 242). However,

a

is

that

modem, and messages

odic basis.

If the

uucp addresses may many uucp addresses is

the mail cannot be delivered

made

not

and

within

bounces.

it

this,

bounce. The primary cause are linked to a

network via

from a mail server on a network on a

are taken

connection

uucp emulates

not a direct network connection. Because of

is

mail sent to or responding to

of the bounced mail

uucp

throughout the world for the remote copying

some

Some

set

peri-

amount of time, then

mailers can handle uucp-

type mail addresses and will try to resend the mail. Others will simply hiccup.

Below is a short list of more obscure, but valid, email addresses which show some of the combinations of notations I have mentioned. DIALRA@asuacad bitnet 74236 2754@compuserve com [email protected]. vf .ge com hisrov@cirrus com skij ig@smith. rise rockwell com Claris qm!Norman_Rockwell@ames .arc .nasa.gov .

.

.

.

.

.

.

!

Notice that the net

is

first

example

is

an address to an organization called bitnet. Bit-

an alternative network, like uucp or internet.

It

should be noted that there

are different networks around the world, that there are going to be

and

that the user

new

ones,

how

to address

supports a more direct form of

communi-

should become comfortable with figuring out

mail rather than focusing on a specific one.

2.6

Electronic Talk In

addition to electronic mail.

cation called electronic talk, All

you need

to use

it

is

UNIX talk

is

very similar to a telephone conversation.

the recipient's userid

and mail address, as

in email.

43

2.6 Electronic Talk

Unlike email, where you can send a message to

many people

at

once.

UNIX

does not come stock with a means for teleconferencing using talk.

Talk Etiquette

2.6.1

Like email,

talk

who happens

has

its

own

set

of guidelines. Because you can

'"dial"

any

you could talk to someone with whom you shouldn't be talking or who doesn't want to talk with you. There are ways around this, of course, as you will see. The essential rule user

of etiquette

is

be logged

to

to

is

entirely possible that

Sometimes talk

is

someone unless you have some introduction to them in the past.

•

ideal.

it

simple:

talk

Do

in.

You

not

need

will

not a useful

way

to

sent

them mail or otherwise had

communicate, but sometimes

to figure these things out

it is

on your own. but here are some

pointers.

Trying to

•

talk

a long distance

is

less than ideal

because the signal must

bounce off many machines and response times may be high. Trying to

•

talk

during peak periods could get frustrating, also because of

performance.

Trying to

•

talk about personal

matters can get

awkward because one cannot

read inflection or expression from the responder's words or face.

Other forms of etiquette apply

in talk,

probably more so because the con-

is "live." In the section on email it was suggested that you edit your messages before sending them. Using talk you will be not be able to do any editing, so it is essential that you have a good attitude and be willing to explain

nection

what you mean by your comments. Try not to leave things person doesn't have to guess what you mean. 2.6.2 It is

Invoking Talk

easy to

dress,

out. so that the other

and

talk to

(2)

logged on are

someone. You need

to

know

( 1 )

their userid

and mail ad-

Two ways to find out if issuing a who and looking

whether they are logged on. (

1

)

userid. If they are

fingering them, or (2)

they are for their

logged on. you can issue the following command:

localhost> talk jqsmith

which

is

the simplest

form of the template

talk userid@domain where "domain"

is

the

machine address. Note

that a full address

may be

re-

.

44

Chapter 2 Electronic Communications

quired, and that the address could be any legal mail address.

talk

When

first called,

sends the message:

Message from TalkDaernon@domain talk: connection requested by your_name@your_machine talk: respond with: talk your_name@your_machine .

to the user

.

.

you wish

talk

to

At

to.

this point, the recipient

of the message

should reply by typing:

talk your_userid@your_domain

It

doesn't matter from which machine the recipient replies

logged

in

on many machines),

person's machine

is

(i.e.,

they could be

same and the source appropriately noted. Once communication is established, as long as the userid

is

the

two parties may type simultaneously, with their output appearing rate windows, which will look like the one below:

the

in sepa-

localhost> talk [email protected] [Your party is not logged on]

localhost>

Your typing will

echo

in the

will

always echo

in the

lower window. Typing

upper window, and

that of

your friend

will cause the screen to

be

and kill characters will work in talk as normal. If you are having awkward problems in talk, then the most likely is that the terminal's termcap is incorrect (see Chapter 5. page 143) for details on working with terminal characteristics. The most obvious problem reprinted, while your erase,

you find problem is

that

having a single character echoed per

Exiting Talk

2.6.3

To

talk,

exit

moves 2.6.4

line.

your interrupt character . talk then bottom of the screen and restores the shell prompt.

just type

the cursor to the

Talk Protocol

Although both parties can type simultaneously, "talking"

is

having a dialog.

kind of protocol for establishing the end of a

You should decide on some ment. One such method is to continue to pause,

and then type

a

com-

typing until you get to where you want

double carriage return.

You may

also decide to use a

2.7 Electronic

45

News

It is up to you and your friend to agree, or at least you to do something that will enable your friend to distinguish between your comments. Otherwise they will all run together and you end up with mush, especially when the screen scrolls or refreshes.

special character or phrase.

for

Talk Permissions

2.6.5

Permission to

can also

talk

receive

talk may

set this in

your

be granted or denied using the .

cshrc

file.

For example,

messages, then you would

set

mesg

mesg command. You

if in

general you want to

as follows:

localhost> mesg y

Conversely,

you want to turn messages off so same command as follows:

if

ered, then use the

that

you cannot be both-

localhost> mesg n

These are both examples of usage one of these commands into your

2.7 Electronic

.

at the

cshrc

command

file,

and

it

line.

will

You can

also put

become your default

News

Electronic news, like email and

talk,

is

a

method of communicating with

oth-

computer users. Unlike email and talk, that single out a few users, or a sinbroadcasts messages to a particular newsgroup. A newsgroup is gle user,

er

a

m

name

1

associated with a forum on a particular topic.

The messages associated

with the newsgroup are maintained on a blackboard.

of

list

whose information

is

available to a large

group's messages are thus available to anyone

A

blackboard

number of

who

entities.

is

a type

A

news-

subscribes to the news-

group, and anyone can post to or follow up on messages posted to the newsgroup.

newsgroup are maintained across the Reading news may end up being a terrific

The messages associated with

network and updated regularly.

a

waste of time, but everyone should be introduced to

its

use.

You have been

forewarned.

News

is

a feature of the internet that arose

from the need for governmental

asencies to communicate with one another and their contractors. The use of 1. There are many incarnations of electronic news, of which rn is but one. Your institution may use news. xrn. trn. rnews. or others. In addition, there are other services which are similar to news, such as gopher and the World Wide Web, which are information servers, and ire. which is a

multiple person talk program. Seek assistance for these services locally.

4b

Chapter 2 Electronic Communications

this facility has grown over the years and has led to a proliferation (type newsgroups sometime, but be prepared for a long wait) of newsgroups. Some of these newsgroups are extremely helpful for transmitting ideas, software, announcements, copies of papers, and so forth between institutions and individ-

uals.

Conversely,

many

of the newsgroups are purely social in nature, mas-

Some do

querading as technical bulletins.

needs just like other dot In this section

newsrc

.

els are

some

common commands

for using the various

this feature,

and because many

fluence or import in your field,

it

pays to use caution

You simply

once. Be-

in posting

in-

and responding

this in

mind and

find

could help them get a job. or into graduate

never know. There are a few guidelines that can be used to

smooth your introduction

When

who

at

audience could be people of

in the

newsgroups. Unfortunately, often users do not keep

themselves flaming someone

•

lev-

Etiquette

allows a computer user to express ideas to a large audience

school.

news

presented for reference.

cause of

to

up

etiquette guidelines associated with news, setting

environment, invoking rn, reading from and posting to news will

News

2.7.1

.mailrcand .mh_prof ile).

files (e.g.,

be presented. In addition,

News

The .newsrc

a shell script for initializing news, and can be tailored to suit the user's

file is

a

1

not even masquerade.

to

news, as presented below.

posting to newsgroups, never cross post unless you

are doing. Cross-posting

is

when

a user has a

than one newsgroup. Because this

is

know what you

message targeted toward more

potentially wasteful of resources, be

was made to before doThe worst-case scenario is when the postmaster is made you are not using news properly, in which case you could lose

careful to check the

newsgroups

the original posting

ing a follow-up.

aware

news •

that

privileges.

When

posting to newsgroups,

any given

you make a 2.7.2

remember

field are reading the

fool of everyone

that the

newsgroup.

If

most important people

you make a

on your network, and they

in

fool of yourself,

will

remember.

Invoking rn

Using news

is

quite easy.

The UNIX command

is

rn

(for readnews).

localhost> rn

When

rn

is

typed for the

first

time, the system will present

you with

a

(long) introduction to reading news. In this introduction, which you should

I

.

For a more complete history of the origins of email and news, add

ers

to your

.

newsrc.

news announce newus.

.

.

47

News

2.7 Electronic

news etiquette and instructions. At the same news server will present you the option of subscribing to one or more newsgroups. The list of newsgroups is very long and you could spend hours simply saying 'n" to every newsgroup you do not want to subscribe to. Suffice it to say that you can always subscribe to a newsgroup, so it is best to exit news

read,

is

a thorough discussion of

time, the

and then

shortly after this question/answering session begins

.news re to the

file that will

UNIX

shell

be created.

exit

rn, keep typing

later edit the

'q' until

you return

prompt.

2.7.3

Reading News

rn.

mail,

like

To

has

its

multiple levels within

own environment and its

environment

to

prompts. Unlike

mail, rn uses

keep track of newsgroups and mes-

news environment:

newsgroup selection Each level has its own commands and prompt, so using rn can take some getting used to. Below I have included an entire sample session using news on the host SFSUVAX1, spread across a number of examples. sages. There are three levels in the

level. (2) article selection level,

and

(3)

( 1 )

pager selection

level.

localhost> rn (Revising soft pointers--be patient.) Unread news in comp. lang. lisp 63 articles Unread news in comp. lang. lisp. franz 2 articles Unread news in comp. sources .wanted 193 articles Unread news in rec .humor funny 3 8 articles Unread news in rec scuba 159 articles etc Checking active list for new newsgroups... Newsgroup alt.allsysop not in .newsrc--subscribe? [ynYN] n Newsgroup alt .bbs .allsysop not in .newsrc--subscribe? [ynYN] n Newsgroup alt .binaries .pictures .d not in .newsrc--subscribe? [ynYN] N .

.

(T)

continued...

This

The

first

first set

portion of the session illustrates what happens

of items

(i.e..

on the

left) is

a

list

when rn

starts up.

of the newsgroups currently sub-

The newsgroup names are organized from "comp. lang. lisp" is a computer science topic, the subtopic is programming languages, and the subsubtopic is the LISP programming language. Some of the names can be difficult to understand. On the right you are told how many articles were posted since you last read a particular newsgroup. Some groups will accumulate artiscribed to (e.g., rec.humor.funny).

general to specific. For example, the newsgroup

cles at an alarming rate. Note,

of the active

(i.e..

from the

"etc.** that this is

groups that have been added to the network since long, so

I

only a partial listing

subscribed to) groups. The next set of items are

used the capital

"N'

response

I

(at 1), after

last

read news.

responding

new newsIt is

'n' to a

rather

few. to

]

48

.

Chapter 2 Electronic Communications

stop the process.

The

reply from

rn

is

shown subsequently.

(I'll add all new newsgroups (unsubscribed) to the end of your .newsrc.) (Adding misc. writing to end of your .newsrc unsubscribed) (Adding news members to end of your .newsrc unsubscribed) (Adding news software. readers to end of your .newsrc unsubscribed) (Adding rec.games.board.ee to end of your .newsrc unsubscribed) (Adding rec .pets cats to end of your .newsrc unsubscribed) (Adding rec sport .volleyball to end of your .newsrc unsubscribed) (Adding soc culture italian to end of your .newsrc unsubscribed) (Adding vmsnet tpu to end of your .newsrc unsubscribed) .

.

.

.

.

.

.

continued...

This means that

I

will not be

asked those questions anymore, but that

subscribe to those groups in the future will

happen

is

that

rn

member

that the first

whether

I

want

if I really

will start reviewing

group was "comp

to read

any of those

.

type

'n,'

The next

to.

I

can

thing that

each subscribed newsgroup. Re-

lang .lisp." rn now prompts me

articles.

This

******** 63 unread articles in comp. lang. lisp-read now?

I

want

is

the article selection level:

n

[ynq]

so rn continues on to the next group:

******** 2 unread articles in comp. lang. lisp. franz-read now? [ynq] n ******** 193 unread articles in comp. sources .wanted-read now? [ynq] n ******** 38 unread articles in rec humor funny-read now? [ynq] = .

When

.

the user types an equal sign (=), this tells

portion of their subject field (similar to

mail's

rn

to

'f ' and

list

the articles by a

MH's

'scan' com-

mands), and enters the user into the article selection level for the group "rec 673 674 675 676 677 678 679 what-

.

humor funny." .

Stanford research Forbidden Zone #121 (Relative Value Ranking) Editorial Policy on Offensive Jokes -- Monthly Po Ghandi and British Police Proposed Improvements to World League American Fo Judges, Lawyers and Whales A hard thing to give up. .

npxr?

[

npq continued...

:

News

49

article,

type the

2.7 Electronic

This partial

list

number shown on

shows

the

left.

the articles

by number. To read an

For example,

we

will read article

number 673, hop-

ing for a chuckle.

What npxf?

[npq]673

Article 673 (37 more) in rec .humor funny (moderated) Subject: Stanford research Message- ID: From: [email protected] (Edward L. Rodriguez) Date: 4 Jul 91 07:20:06 GMT Keywords: topical, chuckle .

.

Lines:

10

My first atttempt at an original joke: How many Stanford researchers does it take to screw in a lightbulb? Three. One to hold the ladder, one to turn the bulb, and one to bill the government for the house. Edited by Brad Templeton. MAIL your jokes (jokes ONLY) to [email protected] If you post instead of mailing, it screws up the reply-address sometimes. Attribute the joke's source if at all possible. A Daemon will auto-reply. End of article 673 (of 710) - what next? [npq] q continued...

at the bottom of the posting ("Edited by ..."). This newsgroup is moderated, and all postings are screened by the moderator. Many newsgroups are unmoderated, and posting a message is discretionary. When rn has gone through all the newsgroups you have subscribed to, you will see the following message:

Note the portion

means

that this

******** End of newsgroups- what next? localhost>

at

which point you

2.7.4

will

[npq]

q

be returned to the

command

shell.

Posting to a Newsgroup

Posting to a newsgroup means to submit an article to the newsgroup. The pro-

cedure

is

gerous

tactic).

You can edit a file or write one "on the fly" (sometimes a danThe command for posting to a newsgroup is Pnews. To use the

simple.

Pnews command,

type the following

line:

localhost> Pnews newsgroup

where "newsgroup"

is

the

newsgroup you wish

to post to.

then interrogate you for a few minutes to determine

how

The system

to set

will

up the posting

DO

Chapter 2 Electronic Communications

for distribution, will ask for an editor to use, and will then ask for a file to use.

These

have defaults

all

parentheses) and this

(in

is

straightforward enough.

When you are done, the system asks you "What now?" just as in MH (see page 35). When you eventually reply with send, the message or news posting speeds along

Setting

2.7.5

The

first

time

Up

rn

the

.

newsrc

want to unsubscribe the message number

to maintain

then you can edit

file,

your newsgroups.

your

in If

with your favorite editor.

it

with an exclamation point

list

To

see the effect of the

If

to

you

before

(:)

resubscribe, simply

on the execution executed whenever you invoke .

is

To

!).

(

newsrc

home

you want

newsgroup, then simply replace the colon

procedure shown below

rn, the rn startup

named .newsrc

will create a file

it

rn how

to a

reverse this procedure.

of

News Environment

invoked

is

directory which instructs

modify the

A short list of news commands is included below.

merry way.

its

file

rn: •

rn

will look for

newsgroups. find one, •

rn

If

will

it

your

rn

back

your

will input

.

newsrc

file,

which

is

your

list

of subscribed-to

newsrc, it will create under the name oldnewsrc.

doesn't find a.

.

it

up

one. If

it

does

.

newsrc

file, listing

out the

first

several

newsgroups

with unread news. •

rn .

it

will

perform certain consistency checks on your

newsrc

up for you, but you may have

could be a •

out of date in any of several ways,

is

rn

2.7.6

An

rn

.

newsrc.

If

your

warn you and patch

to wait a little longer for

it

to start

up

(this

lot longer).

will next

check

to see if

any new newsgroups have been created, and

give you the opportunity to add them to your •

rn will

goes into the top prompt level

News Command Reference

-

the

.

newsrc.

newsgroup selection

level.

— Abridged

abridged set of commands for each of the three news levels

is

provided be-

news on your own. The commands for rn are startup, newsgroup selection, article selection, and

low. Use them to set up and read

divided into four sections:

pager selection.

Newsgroup

Selection Level

In this section the

newsgroups

in

prompt looks

words "next" and "previous" refer to the ordering of the .newsrc file. At the newsgroup selection level, the

your

like this:

******** 63 unread articles in comp. lang. lisp-read now?

[ynq]

2.7 Electronic

The following commands can be used Table 2.8: y,

at the

newsgroup

News

51

selection level:

rn Newsgi 'oup selection commands

or space

=

Do

this

newsgroup now

Do

this

newsgroup now, but

list

subjects before displaying arti-

cles

n

Do

not do this newsgroup now, go to the next newsgroup

P

Do

not do this newsgroup now, go to the previous

1

Do

not do this

$

Do

not do this newsgroup now. go to the end of the newsgroups

newsgroup now, go

to the first

newsgoup

newsgroup

list

g newsgroup

Go

/pattern

Scan forward for a newsgroup matching pattern, e.g., use ? to match a single character, * to match any sequence of characters

?pattern

Same

u

Unsubscribe from current newsgroup

c

Catch up

q

Quit

X

Quit, restoring

to newsgroup; if you aren't a subscriber, you will be asked if you want to subscribe and how you want the newsgroup placed

as

/pattern,

— mark .

all

newnewsrc.

unread

newsrc

you would have had .

but search backward

in

articles in this

newsgroup

to its state at start of

you had exited with case you didn't really want if

rn; the 'q' will

as read

.

newsrc be called

to type 'x.'

Article Selection Level

On

the article selection level

article

before the article

comes

at the

END of the

is

you are not asked whether you want

article.

The prompt

the following:

End of article 673

(of 710) -what next?

to read an

displayed; the normal article selection prompt

[npq]

at the

end of an

article

looks like

52

Chapter 2 Electronic Communications

The following

Table 2.9: n,

rn

Article selection level

space

commands

are the available

in the article selection level:

commands

Scan forward for the next unread

N

Go

P

Scan backward for the previous unread isn't a previous unread article

P

Go



Refresh the screen



Restart the current article, and decrypt as a rot 13 message

X

Refresh the screen, and decrypt as rot 13 message

number

Go

pattern

Scan forward for

?pattern

Scan backward for

r

Reply through net mail

R

Reply, including the current article in the header

f

Submit a follow-up

F

Submit a follow-up article and include the old article with lines prefixed either by ">" or by the arguments to a "-F" switch

c

Catch up

u

Unsubscribe

Save

List subject of unread articles

s

destination

=

It

to the next article

to the

numbered

in this

article

u

if

there

containing pattern

article

containing pattern

newsgroup;

to this

i.e.,

(i.e.,

mark

all articles

and X commands

un-encrypt) messages that are posted that

The encryption schemes in

as read

sh

Although

this

established for maintaining the content of

ant to read postings,

generated

newsgroup

to a filename or pipe using

and decrypt

file

article

are

meant

to

may seem

news

the postmasters at each institution to maintain control users.

here

article

sensitive or offensive to certain groups.

no means

article; stay

to the previous article

should probably be noted that the

to encrypt

article

(if

are used

may

postings.

It is

who

is

left to

and peace among

inform readers that they

order to avoid being offended. Those

be

odd. there

their

may

not

decr\ pt the

2.8 Exercises

messages have no the intent of the

real

53

and Sample Quiz Questions

complaint because they were warned ...

at least, that is

mechanism.

Pager Selection Level At

the pager level (within an article), the

prompt looks

like the following:

-MORE- (17%)

where the percentage (here \19c) means been displayed so

Table 2.10:

rn Pager selection

far.

The commands

level

that this

is

how much

of the article has

available at page selection level are

commands

X

Display next page and decrypt a rot 13 message



Display one more line

q

Go to the end of the current article (don't mark it either as read or unread)

3

•

What

is

the

•

Provide an example of

symbol used

mail message

for in

MH equivalent to the

lists?

>?

how each would

appear

in a

message

list:

Problem 4

MH commands to do the following:

Provide the

Get new messages into List all

messages

Respond

to

in

MH:

your working mail folder:

message number 32:

Put message number 32 into your "Personal" mail folder: Exit

Problem 5

What

is

MH:

the proper

rn command used

to catch

up on unread news? To

search for a specific piece of information in news

Problem 6

List three types of

do not occur this is a

in

problems posed by electronic communications

normal dialogs between people. For each, describe

Define 'flame.' List two practices

Problem

Answer •

that

why

problem.

Problem 7 X

articles'.'

avoid giving or receiving flames?

the following questions about

What of

to

rn

news

command

is

used

to

rn

list

the

articles within a particular

numbers and subject

line

newsgroup?

•

What command

is

used

•

What command

is

used to Follow up to a newsgroup posting

to

add

a

newsgroup? '

2.8 Exercises

Problem 9

Problem 10

and Sample Quiz Questions

55

Describe the name address convention, and give three examples of

What

stitution types

commonly

someone with

the following address:

Name

used.

is

the origin of a

irisa irisa .

.

f r?

the file that contains the following line. Explain the

each term

in-

message from

meaning of

in the line.

130.212.10.102 sfsuvaxl.sfsu.edu sfsuvaxl vaxl

3.1

Introduction and From

Scope

a user's viewpoint, an operating

system consists of different programs

executed to perform specific tasks. Programs that perform system-re-

that are

lated user instructions are called

commands. Commands

are distinguished

from applications and user-defined programs, which perform non-system-related tasks. All of the

UNIX it

file

programs and data

that reside

system, and each must be organized

on the system make up the

in a consistent

manner so

that

can be used when needed. This chapter presents the organization and manip-

ulation of

programs and data

in the

UNIX

operating system.

The

topics cov-

ered in this chapter are listed below: File

system components: directories and

files

UNIX commands Directories and directory manipulation Files File

and

file

manipulation

system security

UNIX file system is an organization of files and directories that enable perform its function. Knowing how the UNIX file system is organized is important in knowing how to use When you have completed this chapter, you should understand how the UNIX file system is organized, and The

UNIX

to

it.

how

to

of the

move around

file

system

within

it.

in different

You

should be able to manipulate the contents

ways. For example, you should be able to

contents of a directory anywhere in the currently located in the fde system.

file

You

list

the

system, regardless of where you are

should be able to change your loca-

57

58

Chapter 3 The UNIX

tion to

File

System

anywhere

contents of the eral, a file

in the file

file

system, and you should be able to manipulate the

system: to create, move, rename, or execute them. In gen-

system can reside on any type of storage device. For example, a disk

drive, a diskette drive, an optical drive,

tems on them. By mounting a device,

UNIX file

system and

tended scope of

this

its

and a tape drive can

its file

The mounting of file systems

users.

course and

is

have

all

file sys-

system can be made visible

mentioned for

is

beyond

to the

the in-

clarification purposes. File

system mounting can only be performed by administrative personnel. Beginning with this chapter, It

will

be assumed

I

that,

at the end of every example. command name and arguments are invoked,

will cease to print a

when

a

they are followed by a carriage return.

3.2

File

System Components In

UNIX,

file is

there are essentially

two types of structures: directories and

a meaningful sequence of information that has a

enced. Programs and data are types of

files. Files

name

files.

The

file

A directory can orga-

files.

system describes the organization of directories and

and be organized by other

rectory, called the root directory,

A

Files cannot organize anything except in-

formation; neither directories nor other

rectories can organize

files.

can be refer-

are organized in directories,

so a directory can be thought of as a folder or organizer. nize other directories as well as

that

Most di-

files.

one

di-

which cannot be organized by (contained

in)

another directory. The root directory

is

directories.

There

is

often visualized as the top of a tree's

root system or the branches of an inverted tree.

The

directories

which the root

directory organizes can be thought of as branch points to different parts of the root system (see Fig. 3.1). Every directory and file originates from the root directory, tree.

and every branch point actually describes a mini root system or sub-

Every directory of the

file

system eventually terminates with a

directory that doesn't organize anything, called an

nating

file is

often called a node of the

nothing can emanate from

it.

file

empty

directory.

system, or a leaf of the

file

A

tree,

or a

termi-

because

3.2 File

Figure

3.1

:

The UNIX

file

system

Ctmp^

CaevJ

(_users^

Q bin}

(^tom^

(^blevine^

is

System Components

comprised of directories and

GD

(1)

Root Directory

•

(2)

Subdirectory

•

(3) File

(L

b

"\^

]

Directories and files are organized by function.

number of primary subdirectories. For example,

are contained in a directory called "usr."

found

files

(jhodges^

C^CCod^

a

59

in the directories

Many

The all

root directory contains

of the users' directories

of the system

"bin" and "etc." Other system

commands

are

directories are listed

below:

localhost> Is -F

backups/ bin/ dba/ dev/ etc/

/

genvmunix* lib/

lost+f ound/ mnt/ opr/

pak_admin/ pcs750 .bin* public/ quotas secure/

This example slash

(

/

).

is

file.

Note

that

for an executable

by

is

which

is

denoted by a single

name, root does

not.

Any

directory

The contents of the root diFor example, the item "vmunix," above,

called a subdirectory.

"vmunix"

files.

followed by an asterisk ( * ). This is the notation meaning that it is a program." Directories are denoted name. Thus the directory " 1 ib" is listed as " 1 ib / " in this

file,

a slash after their

usr/ var/

directories have a

rectory can be directories and a

vmunix*

ultrixboot

a listing of a root directory,

Whereas most

'below' the root directory

is

vmb. exe*

sys/ tmp/

is

.

60

Chapter 3 The UNIX

File

System

Below is a partial description of the contents of some of the major subThe contents of these directories changes slightly from one UNIX

listing.

directories.

implementation and platform to another.

Table

Standard UNIX top-level directories

3.1

/bin

System binaries and many of the system commands

/usr

Manual pages, user

/lib

System

/etc

System commands

/dev

Hardware device configuration

/tmp

Temporary storage

libraries

These directory names and

UNIX

directories, applications

files

(publically read/writable)

their contents are

an important part of the

operating system, because they have been standardized across the dif-

you get an account on a network somewhere other than where your current account is. and you want to know where the contributed software is. then if it was placed in "/usr /local/bin" or "/usr/contrib" on your old system, that would be the first ferent platforms that use the operating system. If

place to look on the

new

system.

tem, you are simply going to

aged to do ing the

so.

file

This

the best

is

system, and

it is

To

find out just

what software

is

on your sys-

have to go looking around, and you are encour-

way

to learn about the

the only

way

commands

to find those little

for manipulat-

jewel programs

that aren't publicized but are available nonetheless.

Naming Conventions and Paths

3.2.1

Each directory and path

is

file in

the file system

a concatenation of directory

is

associated with a path.

names, separated by slashes

An

item's

(/), starting

with the root directory and ending with the directory in which the item resides.

The

root directory

Any full

is

designated by a lone slash

(/).

path that begins with the root directory (/)

path.

A

full

path

is

rectory can be referenced with a full path, although

1

2.

Sec Section This

is

not

3.4.1

.

page 69 for details on

necessanK

true.

is

called an absolute or

a path that starts at the root directory.

this

nomenclature.

See Section 3.6.2 tor

details

it

is

Any

file

or di-

rarely necessary to

write the entire path out in

full.

All other full paths start with a slash to denote

that every path originates with the root directory.

"jhodges"

belonging to the user

61

UNIX Commands

3.3

For example, the directory

resides in the "fl" subdirectory under

"/usr," which is a subdirectory off root. So my directory, jhodges, resides three levels below root. The path for the files and directories belonging to

jhodges

is

denoted as follows (see bold

line in Fig. 3.1):

/usr/f 1/ jhodges

The root directory has no name, and all other names specify The path is our means of finding and executing programs in the

To

tem.

use the path effectively,

it is

important to understand the syntax asso-

UNIX commands and to know how to UNIX commands. For the remainder of this chapter,

obtain information about

ciated with

Ch3

manual, examples will be provided from the

this

subdirectories.

UNIX file sys-

and

in general

"UNIX/Ch3"

throughout

directory.

It

should be noted that any modifications to a directory require write permission to the directory

to

(covered

make modifications

Section 3.6.2 of this chapter).

of these directories,

your own.

else's directory except

similar

in

to either

You

are

You

will not

be able

anyone perform the same or

or, in general, to

encouraged

to

your own directory, and even to excommands will work in directories not owned by you. look at the "UNIX" directory to compare what you do to

commands you

are reading here in

periment and see which

You

are

welcome

what you see

to

in the

manual. They should be similar,

if

not identical.

UNIX Commands

3.3

When

users log on, the

first

thing they see

about what happens to produce the prompt

can be manipulated. For now, to the file system.

it

is

is

More is explained and how these events

a shell prompt.

in

Chapter

important to look

5,

at the

prompt with respect

Consider the prompt below.

localhost>

When you mand

see this

interpreter. This

grams and they

1.

fl is actually a

file

2.

mounted

file

are evaluated

system of

The "jhodges"

As opposed

ing.

its

and executed now.- Each

own. and looks

UNIX command

like a subdirectory in the local

is is-

UNIX

system. directory

is

provided as a template to

a variety of responses that are not clearly 3.

prompt you are in a command shell. A shell is a comthat you can issue UNIX commands or run pro-

means

to a batch job,

which

is

shown

in a

illustrate the

use of

commands and

to

show

simple directory such as "UNIX."

submitted altogether and run

later

according to priority rank-

62

Chapter 3 The UNIX

File

System

sued with the following syntax:

command -name [command-options] [command-arguments] command- opt ions

where

(often called keys) are single or multiple charac-

how the command response is displayed, and command- arguments are the user-provided items that the command operates on. Some command options or arguments may be optional, and will appear in square brackets in the command template. In general these will generally be noted in the text. In UNIX, most every command argument will be a directory, which are used

ters

a

file,

to

to specialize

or a path to same, so you, as a user, will have to

do (what command you wish

know what it

to execute, its options,

and

its

is

you want

required argu-

ments) before you can do anything. Let's say that you successfully changed

your password

in the first

chapter of this manual.

Then you

correctly issued the

passwd command: localhost> passwd

passwd is

a good//rs/

command

because

it

performs a necessary task of pro-

viding security for your account, and because

ments.

Many

file

it

system commands can be used

requires no options or arguin this

way. Others are more

What do you do when you do not know the name, options, or arguments of a command, even though you know what it is that you want to do?

complicated.

3.3.1

When

Getting Help about

Commands: Online Manual Pages

learning about any operating system,

it is

perfectly normal not to under-

you need them. This is awkward because, without knowing what it is that you need help on. or what command it is that you need to execute, you will not know where to look for the answer. stand the use of particular

The its

commands

UNIX operating system is

nuances. So

there

is

until

so large that no one person can

remember all of

an online version of the manual that you can call on to

find out syntax and usage of any

UNIX command. What command

is

more, you will not

The drawback is that They are comsomeone to reneeded by information have only the save and space, pact to is necthis is all that fresh their memory of how to execute the command. Often have to know, a

the

priori,

manual pages

essary, but

what the name of the

are written as a reference

you need

to

know how

is.

and not as a

to read the

tutorial.

man page

or you will be as con-

fused as before you began. There are three things you need to know to use the

man

pages: (1)

how

to

invoke them. (2) their general format, and (3) how

search for what you are looking

for.

to

.

.

.

.

.

Man

Page

The command is man, which you type prompt. The general usage is shown below:

Using the online manual the shell

63

UNIX Commands

3.3

Invoking the

)

.

simple.

is

at

man [subsection] command -name command name, "subsection" is an optional (as noted by the square brackets) subdirectory name, and "command -name" is the name of some command you wish information about. For example, if you type: where "man"

is

the

localhost> man man

man Name

(

1

V ^\

man - displays manual pages online subsection Syntax man -k keyword. man -f page_title. section man options -rof f_options page_title. man options section page_title. section page_title /usr/bin/man option /usr/bin/man options section page_title. Description There are two man commands: /usr/ucb/man, and /usr/bin/man. For most users, /usr/ucb/man is the default man command. The command which man shows you which man command is the default. The recommended default is /usr/ucb/man. .

.

[

]

[

[

]

[

]

[

]

[

]

.

[

is

]

.

.

]

"manual" page, or

actually a

.

]

.

[

the system displays a

This

.

.

[

uals.

.

.

.

.

.

man

]

.

.

page describing

condensed version of the

full

system

the online

man-

command refercommand

ence manuals that are available for the computer. The 'subsection'

argument

is

to look for

optional because the system has a set of default locations in which

The "subsection' when provided, overrides the listing that 'man (1) has been labeled. The '1' refers to man library where this command's man page resides.

manual pages.

search. Notice in the

a subdirectory in the

'

If you know what sort of task you want to find out about, but not the commands associated with the task, then there is a modification of the man command you can use. The modification makes use of what is called a command

option or key.

1.

Many command'sarguments

square brackets.

If a

have default values, which are normally identified by a value

value isn't provided for an argument, then the default value

be confused with a command's optional arguments which are also shown

in

is

in

used. This could

square brackets.

64

Chapter 3 The UNIX

File

System

localhost> man -k manual where the '-k' is a man command option. Virtually every UNIX command has options. The argument "manual" is called a string. The '-k' man option

means "do ual,'

a search through

and return a

mand

list

of the

all the man pages for a string equivalent to 'manman pages that pass the test." Thus, after the com-

issued above, the listing

shown below

es of information in the listing below:

section for the

command, and

( 1 )

is

displayed. There are three piec-

command name,

(3) the subject

(2)

man

library sub-

header for the command.

localhost> man -k manual - create the cat files for the manual catman (8) - displays manual pages online man (1) - manually manipulate the routing tables route (8c) - translate version 6 manual macros to version 7 macros trman (1) - locate source, binary, whereis (1) and or manual for program

The items on

the far left are

command names,

so you can then issue a

man

command with one of these items as the argument. There are a number of places a man page might be found. Many manual pages are located in the directory "/usr/man." The numbers in parentheses next to the command name designate a subdirectory where the man command should look to find the man page file.

For example, items with a

directory under the standard the

"NAME"

line in the

( 1 )

man

man page

after

them can be found The items on

directory.

the string in the

man

for.

left is

"man

(

1

sub-

the

left.

This

This provides the context of

page. For example, after issuing the

above, one of the items on the

"manl"

the right constitute

command on

that describes the

item will contain the string you were looking

in the

." )

To

man command,

the right of this item

is

"displays manual pages online ." If you go back and look at the name line for the man man page, you will see that it is the same. There is no difference between executing the 'man 1 man' command and executing the line

the

'man man' command. However, this is because Section of the manual is in a default manpage directory. If the man page was in Section 8. as is catman page, then the only way to read the manual page is to issue the 1

pages the

command: localhost> man

8

catman

Another name, or issue the

I

.

You

will read

more about

alias, for the

apropos command aliases

and how

command 'man

just as

to create

you would

your

o\\ n in

the

-k'

is

apropos. You can

'man -k' command.

Chapter

5.

3.3

65

UNIX Commands

localhost> apropos manual

Man

Page Display Format

Understanding a

what

to expect,

comes

man page

requires

and what order

some

to expect

a palatable task. Otherwise,

it

it

will

"inside" information. If

you know

then finding that information be-

in.

seem impossible. Every man page

adheres to a similar format, as shown below. Not every field will be found in

every

man

page, and not always in the

the standard

Table

3.2:

Manua page 1

man page

same

order: however. Table 3.2

shows

headings and their contents.

entry headings

NAME

The command name and

SYNTAX

The command's

DESCRIPTION

»

A discussion

OPTIONS

A

RESTRICTIONS

«>

Special instructions and caveats

EXAMPLES

A couple

illustrations of

comman

FILES

A

of related

such as libraries

BUGS

Generally system specific, with notes from system programmers

SEE ALSO

Related

legal

a short description of

arguments and

of the command,

discussion of each of the

listing

files,

commands and

its

its

function

their order of

usage, and

its

appearance

history

command's options and

their

usage

options application

information references

Locating Information in Manual Pages

When more

a

man command is issued, the system displays the man page using the utility, more is a command that displays a file one screen page

paging

at a time.

A page is displayed,

and. at the bottom of the page, a highlighted box

is displayed. The percentage refers to you have already seen. If you desire to see more of the file, then hit the space bar. If you want to quit, then type the letter 'q.' To find a particular heading or string in a man page, type a slash, the string, and a carriage return. For example, if you want to find the "Examples" heading in the man man page, then after you have invoked the 'man man' command type the characters that follow, which will appear where the word "more" is displayed.

with a percentage and the word "more" the

amount of

the file

:

66

Chapter 3 The UNIX

File

System

/Examples

where the slash ('/)

is

a called a search

string (or pattern) to search for.

type is

"/examples,"

or

Note

that

command and "Examples" is the UNIX is case sensitive, so when you

"/EXAMPLES," you

the response to this search in the

will see different results.

man command

Below

manpage:

localhost> man man Display offirst screen of man page here

/Examples

.

skipping catman(8) command. Examples /usr/ucb/man Examples The following examples all assume the use of the default command: /usr/ucb/man. The following example shows how to locate reference pages containing

the

keyword

graph man -k graph The following example shows how to display the graph '

'

%

(Ig)

reference

page: % man lg graph The following example shows how to display plot reference pages: % man 1 plot 3 plot --More-- (79%)

The search only succeeds the current display page. If

case, the is

it

word "Examples,"

displayed

at

(

1

),

which

is

if

the search key

"/Examples," current string. You can additional options.

"Examples")

is

not on

close to the top of the screen. In this example,

three lines from the top of the display. If

to search to the next occurrence of

retype

(i.e.,

succeeds, the search will place the key (in this

Examples

in the file,

you

it

you want have to

will either

or you can type an 'n' for the next occurrence of the

type a question mark while

in

more

to get a listing

of

)

.

3.4 Directories

67

and Directory Manipulation

and Directory Manipulation

3.4 Directories

Assuming that you have successfully logged into localhost at least once, that you have changed your password, and that you are familiar with a few things about the file system, then you are ready to explore the file system for yourself. As previously mentioned, this is the best way to build confidence in your

ability to navigate

what goodies are out

UNIX

nipulate

so that

we

files. (2)

(4)

is

be able to

(3) be able

are in the

and

located,

so that

a

it

is

the best

you learn how

to find out

and ma-

to navigate

log on to a system,

good place

way

you

are placed in

to begin. Directories are the lo-

As

data.

users,

we must we can find (

1

are currently positioned in the file system, so that

what we seek,

tains

When you

which we execute or use as

cations of the files

know where we

system, and

file

there. In this section

directories.

your home directory,

and use other

around the

list

to

the contents of a directory to see if

move our

same directory where

be able to create, rename,

present location in the

we wish

the files

move

to

file

it

con-

system

work with

are

or destroy directories. Each of

these topics will be covered in the sections below. •

Current directory

•

Directory contents

•

Change

•

Directory creation

•

Directory renaming

directory

•

Directory relocation

•

Directory removal

The Current/Working Directory

3.4.1

When

users log on to a

home

called their

owned by your

computer running UNIX, they are placed

directory.

Your home

directory

the directory

is

user ID. In general, your user ID and your

have the same name.

home

what

is

which

is

in

directory will

A user's files and directories generally reside

"in," or

"be-

you potentially have your own subtree in the file system. You will be able to move around the file system mostly unfettered, and look at directories and files where you go, but your ability to low." their

home

directory,

meaning

that

write (create, modify, or destroy) files and directories

is

generally limited to

your home directory. As a result, when a user successfully creates a new directory or

1

This

is

file, it

a metaphor, of course.

directories as places to go. 2.

Any

user can create

It is

easier to speak of the

home

will frequently use the location

All this talk of "generally"

places other than your 3.

I

can generally be found somewhere under their

is

meant only

own

directory, but

files

and directories

you

an exception rather than a

in the

when

to directories.

will be able to write in rule.

temporary directory called

deleted on a regular basis by the system administrator or

directory.

directory as a location and other

metaphor when referring

to suggest that, at times,

it is

home

the system

is

"

/

tmp," but these are

rebooted.

68

Chapter 3 The UNIX

File

System

Wherever

the user

directory.

When you

happens

to

be located

called the current or

is

your home directory are one and the same. The working directory because, in general,

ple, if

UNIX commands

made with

tories are being

assume

it

UNIX will

to print a file, then

resides in the current/working directory unless

which

is

the reference to files

important

and direc-

respect to the current/working directory. For

you issue a command

file's location

working

log on to the system, your current/working directory and

can use to find the

file.

assume

you specify another path for the Because of this, it is often nec-

essary to remind yourself of what directory you are currently located

can be accomplished with the ing directory,

command for printing

(i.e.,

in.

This

displaying) the work-

pwd.

Printing/Displaying the

Working Directory

Probably one of the most important

command

exam-

that the file

you where you

will tell

UNIX commands

is

pwd, because this Without such

are located in the file system.

command, you might be able to get around, even create files or directories, but you would never know where you are working from. Because UNIX requires a reference point or path to every command, program, or data file, pwd provides a reference point, pwd is simple to use, as shown below: a

localhost> pwd

It is

not necessary to use

when you

pwd

on the

first

command you

log in the system automatically places

tory. Nevertheless,

would respond

I

had issued the command

in

of a session, because

your

own home

right after logging on. the

direc-

system

as follows:

/usr/f 1/ jhodges

As mentioned

previously, this

is

the notation that the system uses to denote

the location of a directory in the file system,

directory

owned by

response that excellent

way

is

the user jhodges.

displayed will be the

When

its

path: in this case the path to the

pwd command is issued, the pwd command is an

the

full path,

to navigate in the system. In this

thus the

example, the

first

slash

(/).

as

always, references the root directory, "usr" is a first-level subdirectory, and both "f 1" and "jhodges" are other subdirectories. Directories are always separated by slashes, so

it

three levels 'down' in the

is

file

easy to see that the

"jhodges"

subdirectory

There are two shorthand notations for your home directory useful. I,

full

HOME,

that are very

environment variable, and is set path of your home directory when you log in. HOME, if echoed,

One

is

which

is

system.

is

called an

to

as

.

3.4 Directories

below, will return the same as above.

1

and Directory Manipulation

69

Notice that in referring to the

HOME

You

find that

localhost> echo $HOME u s r f 1 1 hodge s '

environment variable, we precede

its

name with

reference operator for

all

variable in the

this is the

a dollar sign

(

$

).

UNIX command environ-

ment/interpreter.

A need

second shorthand for your home director}

to refer to

is tilde (~).

Any

time you

your home directory you can use either of these shorthands

without having to type the entire path which they represent.

localhost> echo usr fl ;hodges

-

Listing Directory Contents

Knowing where you

are in the file system

tents of a director}'

equally important in being able to access and use the

located there.

To

is

list (i.e..

is

very important.

Knowing

the confiles

you will use the meaning that the com-

display) the contents of a directory

command. Is means list the contents of a director}, mand expects a directory as an argument. When invoked without an argument: however, the 2 s command assumes that the directory is the current/working

Is

directory. If an listed. If a

argument

nondirectory

consider the listing of the

1

:

is

given, then the contents of that directory will be

given as argument,

is

home

it

will

be echoed. For example,

directory of jhodges below:

-

:;.!":=:> Is

mail-probs new-net new-topics stud212 testl .c texput log

csc212 cshrc-cognet dead. letter

F90 Mail :-!ar:ual-in-IaTeX

News

fe

P.ZADMZ 7eX3 .

.

f ilterf ile

C

TeX3 7e:~a:ros

foo2

.

.

forward ftp. list mail -elsewhere

bin core

Notice that the listing

tmac

widget

is in

columns, and that

it

is

alphabetical, starting with

The Is command, issued without options, provides this form of listHowever, a listing such as this is not extremely informative. Suppose you

capitals. ing.

1

2.

HOME and home are equivalent for the purposes of the current discussion. Typing Is

$ HOME or

Is ~ would produce

the

same

result.

70

Chapter 3 The UNIX

File

System

have forgotten what directory you are

in,

or

if this is

not your

home

directory,

you may not know what type of items (i.e. their status) are being listed. The 1 s command has a number of options that make directory listings more useful. 4

For example, the -F' option acter that tells

executable

lists

what the item type

file is

the contents of the directory, but adds a char-

A directory

followed by a slash (/), an followed by an asterisk (*), and a link is followed by an at is.

sign (@). Items without something after

ably represent readable

same

them

For example,

are

if

none of the above, and prob-

the "-F" option

is

used on the

directory as above, the result changes:

localhost> Is -F F90/ Mail/

Manual -in-LaTeX/ News/ README. TeX3 .0* TeX3.0/ -* Texmacros/ bin/ core*

files.

is

mail-probs* new-net* new- topics* stud212*

csc212* cshrc-cognet* dead. letter fe*

®

In this example,

rectory,

testl c* texput log tmac/ widget*

filterfile* foo2* forward* ftp. list mail -elsewhere/ you can see

.

.

that the item

"testl c" (at 2) is an Is command, and you should

and

tions to the

that

.

"TeX3

executable read the

.

0"

file.

(at 1) is really a di-

There are many op-

man page (man Is)

to find

out more about them. Two options that are particularly useful are the '-a" (all option and the '-1' (long) option. The '-a" option lists the contents, as above, I

as well as the dot files that usuallv aren't listed.

localhost> Is -aF ./ .

./

cshrc forward login login-original* .mailrc .mh_prof ile .newsrc .old-cshrc* .oldnewsrc .plan .profile* .project rhosts .

.

.

.

.

rnlast rnsof F90/ Mail/ Manua 1 -in- LaTeX News/ * README TeX3 TeX3 .0/ Texmacros/ bin/ core* csc212* cshrc-cognet* dead. letter .

.

.

fe*

.

filterfile* foo2* forward* ftp. list mail -elsewhere/ mail-probs* new-net* new-topics* stud212* testl. c* texput log tmac/ widget* .

3.4 Directories

In this

example, two things are apparent.

command, you can

First, in the

You

see that options can be put together (concatenated), side by side.

put them directly together or you will have to use additional hyphens.

phen informs the command

whatever follows the hyphen

that

71

and Directory Manipulation

is

should

The hy-

not the expect-

ed directory argument. Thus, you can produce any combination of effects that

you want. Second, you see

many more

that there are really

played with the original Is command. The dot

files are

files

than were dis-

those files that start

with a dot (or period), and are often, but not always, used for initializing and

customizing the shell and other applications. In addition, at the top of the listing there are

two

entries for directories

and a double dot

which you have not seen before: a single dot

(.)

UNIX

the current directory.

fde system, the directory labeled dot

is

you are located, dot

will represent that directory, regardless of

double-dot directory

is

'up' through the file

You can is

as

its

In the

Wherever name. The

parent directory, and provides the necessary route

system without using full paths (path names starting from

You can

the root directory). to list dot files

the

(..).

use the capital ('A') option with the

Is

and directories other them the current and parent

use dot or double-dot as arguments in any

command where

command

directories.

a directory

Is is one such command. If you type 'Is ', then it is the same typing Is without any argument, because the dot directory is the current di-

required.

rectory.

see a

.

may appear worthless, you will other commands, particularly when moving or copy-

Although the use of dot

meaning

for

it

with

in this

context

Is

ing files and directories. Using the double dot as an argument to diately obvious, because

is

imme-

you can then see the contents of the directory above

the current directory.

localhost> aastromo abag aberger abierman aelimam ahhsp ajung alanjung

1s

.

.

The

listing

j j

you see above

fl. because "f 1"

in

mmurphy montever moortgat mpearson mreisch ncalgrnt nf isher ngraf ilo

brands edwards jeng jgemello jglenn jhodges j huang j Johnson

compment cpauling davidm dellis dgermann dhof fman dleveen dphsf

is

is

the double-dot can be

resides).

You can

much more

if you cannot remember

sf ch sgill shehadeh shelter shu smedes

identical to the listing for the

the parent directory for

which "jhodges"

sbhimjee scpeo

"jhodges"

command Is /usr/

(i.e., is

the directory

see, then, that listing directories using

efficient than using the full path, especially

the full path.

72

Chapter 3 The UNIX

One

System

File

last

example using Is. You have seen how

current directory and

its

parent, to

by type. You have not seen how

tents

attributes

ownership,

(i.e.,

size,

to list the contents of the

and

the entire contents,

list

to list the con-

to list the contents of directories

creation or revision date,

etc.), all

can be very important depending on what you are trying to do. For use the'-l' (long) option to the Is plays

many

command. Because

characteristics of each item, only

one item

and the characteristics are displayed across the screen, is shown below, followed by "jhodges."

scription

file

this

you can

the long listing dis-

displayed per

is

in fields.

The

line,

field de-

part of a long listing for the directory

[PERMISSIONS] [LINKS] [OWNER] [SIZE (BYTES) where "PERMISSIONS"

by

of which

]

[

REVISION -DATE] [NAME]

columns. The first column idenmeans that the item is a directory, an T means that it is a link, and a hyphen means that the item is a file. The "REVISION-DATE" columns (three) indicate when the file was last revised, and tifies the file

refers to the first ten

description character.

A

'd'

include the date and the time.

localhost> Is -1 total 354

drwx 3 jhodges drwx 9 jhodges drwxr-xr-x 2 jhodges drwxr-xr-x 2 jhodges -rwx 1 jhodges drwxr-xr-x 31 jhodges drwxr-xr-x 2 jhodges drwx 2 jhodges -rwx 1 jhodges -rwx 1 jhodges -rwx 1 jhodges

The

512 512 512 512

45079 1536 512 512

45056 1

1427

29 20:26 F90 12 21:38 Mail

—

16 15:27 News

24 19:46 README TeX3 .

.

1990 14:53 6 18:45 29 20:28 3

4

bin core csc212 cshrc-cognet

listing is alphabetical, starting

"PERMISSIONS"

discussed later

empty directory (512, system, as this

is

e.g. for

TeX3

.

0"

in this chapter.

News,

(at 2) is

with capitalized items.

field of this listing

at 1) is

the overhead required to set

and the notion

Section 3.6.2. The size of an

always the same for a particular

up a directory. The

45079 associated with approximately 45K (kilo)bytes.

listed in bytes, so the

.

17 17:28 TeX3 21 00:47 Texmacros

actual content of the is

®

10:16 Manual -in-LaTeX

2

Again, as before, the of ownership

is

Jan Jun Jun May Jan Jun Jun Aug Mar May Jan

the size of

size of a file

"README.

3.4 Directories

Command

3.4.2

73

and Directory Manipulation

Wildcards

When you issue a command that might equally apply to many items at the same time, you probably will not want to issue the command for each item individually. Rather, you would like to issue the command once and have it execute the appropriate items.

There are several ways

similarly for

all

this task, all

of which use what are called wildcards.

A

to

accomplish

wildcard matches

strings in specific ways, so including a wildcard in the right position

match one or more items. Consider (*).

The

asterisk will

may want

to

list

localhost> Is -1

the

most general wildcard, the

may

asterisk

match any number of any characters. For example, you

the contents,

current directory.

first

You

and the subcontents of

all

the directories in the

could use the wildcard to do so as follows:

*

In a similar vein,

you may not remember the exact name of a command arcommand execute on any similar item, hop-

gument, but are willing to see the

ing that the one you are looking for will be one of them. For example, suppose

you want

to

directory. If it

is

EPS

an

know

the size of a

file

named "vimoves eps" .

you couldn't remember the name of the file (or, at least, that

it

has a .eps

in

your current

remember that name extension), you could use file

but did

the asterisk wildcard as follows:

localhost> Is -1 *.eps

Note

same command was used in both the previous examples, but it was mentioned that applying the Is comnondirectory would simply echo the name. However, when a wild-

that the

the effect is quite different. Earlier

mand

to a

is applied to a command, the current directory The previous command is actually interpreted as

card or other regular expression is

assumed

as a default.

localhost> Is -1 ./*.eps

By

specifying

as in the

of the

more about

files in the directory.

the question

mark

(?)

Two

it

will

command

to

other wildcards that are generally useful are

and the bracket

fect to the asterisk, except

you are seeking, work on a subset

the characteristics of the items

second example, you have forced the

([ ]).

The question mark has

match any single character.

a similar ef-

74

Chapter 3 The UNIX

System

File

localhost> Is Chi? ChlO: Chll:

Chi 2:

REGULAR SCRIPTS SED

AWK Chl3:

ch-ext csh ch-ext2 .csh helloyou. csh looptest csh

onsince csh phones .csh phonesp.csh simplegoto csh

.

.

Chl4: helloyou. sh looptest sh looptestO sh .

.

simpleif csh simpleswitch. csh

.

.

.

untiltest sh untiltestO sh

simplecase. sh simplegoto. sh simpleif.sh

onsince. sh phones sh phonesp.sh .

In this example, the question

.

.

mark

will

match any single

character, and the

UNIX directory matching this template are the "ChlO." "Chll." "Chl2." "Chl3." and "Chl4" directories, so the listing is of the contents of

entries in the

those directories.

The bracket is used to specify particular character ranges. One range would be all the lowercase letters, or a numeric ranges, such as the following: localhost> Is Ch[0-2] ChO:

Compat212

How2UseBBS

Chi: Ch2:

MH-Stuf

SAMPLES

NEWS

which has a similar

effect as the previous

and "Ch2" directories. In general,

if

command,

you have

to

list

specific

the "ChO." "Chi."

numbers, characters,

you are sure are in the filename, then the bracket is most effechave no idea what characters to use. but know how many charthere are. then the question mark is most effective. In any other case the

and ranges

that

When you

tive.

acters

..sterisk is the

way

to go.

Wildcards can be used on any

amount of time and want

to

effort.

One

look deeply into the

file

last

UNIX command,

and can save a large

director) listing option

system

is

when you you want a

useful

for something. In that case

3.4 Directories

recursive descent into the tree and a listing of what sion the

is

is

found as you go. Recur-

a very powerful tool. In the case of Is. a recursive listing

named

directory will be listed and. for every directory

by the named directory, the command

command

75

and Directory Manipulation

which

will be issued again.

The

means

is

that

organized

effect of the

named in the command. Recursive options exist for many commands, because they work so well on tree-like structures such as directories. In the case of the Is command, the *-R' option is used to perform this task. Consider the subtree for "UNIX/ Ch6" below: recursive

localhost> Is -R Ch6 EXERCISES MAN LATEX NROFF-TROFF Ch6 /EXERCISES: Exercise-6 1-input

PRINT-TOOLS UNIX-MAN1-EX

VGRIND

.

TEXFORMATS TEXINPUTS TEXMACROS

PAPER REAL-PAPER RESUME

COMFILES FOO

every directory under the one

Exercise-6 1-output

.

Ch6/ LATEX: BIB

call is to visit

Ch6/ LATEX/ BIB: bibtemplates .bib

bibtex dvi2ps latex

tex

unixmanual .bib

UNIX/Ch6

called a shallow subtree, because

is

it

organizes other directories,

flat

number of embedded levels are organized under "UNIX/Ch6." A subtree has no embedded directories, and a deep subtree has many embed-

ded

levels.

but a small

UNIX/Ch6

happens

the deepest level has been

You have ever,

how

shown

to be three levels

deep (only one instance

many ways; howyou have seen the command work only on the current directory. This seen

to list the contents of a directory in

need not be the case. The Is command, and any other be issued on any path

in the

fde system.

UNIX command,

For example, suppose

that

you

the directory

localhost> Is /usr/man/manl

1

.

The

results

may

not

about the usase.

can are

home directory, and you want to list the contents "/usr/man/manl." You could type the following:

currently located in your

illegal

at

in the display).

make sense

if

the permissions have a directory "closed." but there

is

nothing

of

76

Chapter 3 The UNIX

System

File

Changing the Current Directory

3.4.3

You now have

the ability to determine

where you

are in the file system

determine the contents and attributes of the current directory.

and

to

you want to list or use the contents of another directory, however, you either need to remember the path to that directory, or you must be able to go there (i.e., change the working directory to that directory). The command to change the current directory is cd, for change directory. The simplest usage of cd is without an

cd

argument. Unlike Is, when

home directory is taken as cd are to move down one

is

If

issued without a directory path, the users'

the default directory.

Two other simple examples of

own file system and to move up one directory into the global file system. Remember that the listing of j hodges had a directory called "TeX3 0." You could list the contents of that direcdirectory into your

.

tory, directly,

by typing:

localhost> Is TeX3.0

you actually wanted to do something with more than one file in that directory, then you would end up typing the same paths over and over again. It would be much easier to simply move to that directory as follows: However,

if

localhost> cd TeX3.0

Suppose

that

you have been working

in

TeX3

for a while

.

and want to

go back and work in your home directory: that is, you want to change the directory back to that directory. Any of the following commands will do exactly the same thing from TeX3 0: .

localhost> localhost> localhost> localhost>

cd cd cd cd $HOME .

The

have the same effect when you are

one (cd

.

.

)

will not

system. This

is

because the

The only time

"

.

"

. .

"

. '

if

it

is

the easiest

lowing example.

directory

way

to

to

you are

parent directory, but you can use

times

below is

if

you

are located in a

the first level in your

own

it

your

in the root directory,

anywhere

move up through

file

the parent of the current directo-

home directory is when you are "below" your home directory. It should be noted

first-level subdirectory .

directory or

can point

"

.

you cannot use 'cd

.

have the same effect as the others

home

directory above your

ry.

commands is that, although they all directory, the third located in the TeX3

difference between these four

else.

the

As

file

in a

that

because root has no

a matter of fact,

some-

system. Consider the fol-

3.4 Directories

localhost> cd

II

and Directory Manipulation

../.

Remember

that

the root directory

Then

the

is

we

command just and then

directory,

are in your

three levels

issued

is

home

directory

when we

up from your home directory changing

to its parent. If

you are located deep

are doing, then this

mand above full

is

is

an excellent

way

Concatenating Unix

all

that

in the file

home

of your

system look-

are but. rather,

what

to navigate. If the slash in the

com-

bothering you. remember that the

path of a directory, and that

and

our examples.

to the parent directory

ing around for things and do not recall (or care) where

you

started, in

directories

"

. .

you

"

will be translated into a

must be separated by

slashes.

Commands

Almost every time you change your current directory you contents of that directory to see what

is

there, or

make

will

want

to list the

sure that your current

indeed, the one that you intended to change to. The reason for the you presumably have some work to do in the new location, and probably want to make sure that the files you want to work on are there. The reason for the second is that, before you make any file modification, you want to guarantee that you are working on the right directory. At first, it is probably of value to type the individual commands and see what they do. But this rapidly becomes tedious, and there are ways to reduce this tedium. One way to directory

is.

first is that

perform the same is

to use

set

command

command

shell,

of tasks, in the same order, but to input them

sequencing.

you may

When you

all at

in a

many commands together by separating them When you do this, each command will be executed sequenstring

by semicolons (:). tially and its results (if any) will be displayed on the terminal screen ever appropriate). The general form is shown below: coiranandl;

once

UNIX commands

are typing

command2; command3 ;

.

(or

wher-

.

it doesn't matter how many commands are sequenced. The semicolon is command terminating character, so this is simply a faster way to type out a number of commands that you wish to execute sequentially. Suppose that you

where a

want

to

change your current working directory and

directory.

You

could use

command

list

the contents of the

sequencing (also called

command

new

concat-

enation) as follows:

localhost> cd TeX3.0;ls

Note

that

no spaces were placed between the semicolons and the com-

mands. This was done for

illustrative purposes.

UNIX

ignores spaces so the

78

Chapter 3 The UNIX

System

File

command below localhost> cd TeX3

.

3.4.4

performs the same tasks:

Is

;

Directory Creation

to move around and list directories is fine and good; however, in own directory, you may want to organize your files in some meaningful way. To do so, you must be able to create new directories. A good method for

Being able your

organizing your directory

is

to

break

it

up

into subdirectories according to

function or type. For example, consider the listing for the directory

jhodges

below:

localhost> Is -F

Manual- in-LaTeX/ News/ README TeX3 * TeX3 / Texmacros/ bin/ core* .

mail-probs* new-net* new-topics* stud212* testl c* texput log tmac/ widget*

csc212* cshrc-cognet* dead. letter

F90/ Mail/

fe*

ilterfile* foo2* forward* ftp. list mail -elsewhere/ f

.

.

.

.

The user jhodges has created directories for "Mail," "Manual- in- LaTeX," "TeX3 0," "bin," and so on. The first directory (Mail) was actually .

is where the MH mailer stores the mail for jhodges. The Manual -in-LaTeX directory contains this manual, formatted in latex format. The "TeX3 0" directory contains the sources and binaries for the 3.0

created by the system, and

.

version of tex, the text formatting language used to write

manual. The "bin" directory contains binary

by jhodges. Jhodges could just as or "Code," or whatever.

ments"

er's directory, the

directory,

easily

files

versions of this

have created directories for "Docu-

more highly organized a ussee when you list their home

In general, the

more subdirectories you will files you will

and the fewer executable

The command

many

and other executables created

see there.

to create a directory (subdirectory is the

same

mkdir. For example, to create a new subdirectory Docs beneath directory jhodges, the command would be

thing

I

is

the current

localhost> mkdir Docs

Now

if

we

list

pear. At this point

the contents of

Docs

is

jhodges

(with Is), then

an empty directory.

there, at least with the present level of expertise,

we want we would

If

Docs

to put

be

will ap-

something

in trouble,

be-

3.4 Directories

79

and Directory Manipulation

cause you have not been introduced to the editors, copying, or moving.

Docs, and under

want, you could create a directory under

3.4.5

Renaming

You do

not have to stick to the

it

is

will be

you

Directories

same directory names

that

any time you may change the name of a directory with the

command

If

that, etc.

you

used to do naming and relocation of directories, and

important to understand

"Documents," you would

its

usage.

To rename

At

start with.

command mv.

a directory, say

This

files,

so

Docs

to

type the following:

localhost> mv Docs Documents

mv command requires two arguments. If you provide only one argument. UNIX will complain and do nothing. When you again list the contents of the directory after issuing the command above, Docs is no longer there and Documents is. As you can

Relocating Directories and Their Contents

3.4.6

The

see. the

mv command is also used to relocate an entire directory. Read the man (i.e.. man mv) for more information; however, an example is pro-

page for mv

vided here. Suppose that you have two directories, "bin" and

Code,"

in

your home directory. Suppose

that all the binaries in

"Code/C-

bin

are

C

bi-

you decide to move them under the Code/C-Code directory. If you want to keep the "bin" name intact, then you would issue the mv comnaries and

mand

as follows.

localhost> mv bin Code/C-Code

Because the under

bin.

then,

last

argument

is

an existing directory,

bin directory

you want to relocate and change the name of bin instead, you could type the following:

C-Code.

If

is

moved be C-

to

localhost> mv bin Code/C-Code/C-bin

and

Because the

last

relocate the

bin

3.4.7

You

argument

in the

path

is

a

new name. UNIX

will

rename

directory.

Directory Removal

will

sometimes move the contents of a directory without doing anything and then remove the directory. You can remove a direc-

to the directory itself,

tory with the

rmdir command.

your home directory called

Suppose

that

"bin/C-bin" and

you have a bunch of

files

decide that they should

all

off

be

80

Chapter 3 The UNIX

bin

in the

localhost> cd -/bin localhost> mv C-bin/* localhost> rmdir C-bin

The

System

File

director}'.

Then you can

issue the following

commands:

.

first

command moves you to the director)' where you want to move the The second command moves all of the contents of C-bin

contents of C-bin.

Note the use of the wildcard (*)

to the current directory.

the

C-bin

The

directory.

third

command removes

denote any item in

to

Two

the directory.

errors

can be made when trying to remove directories: (1) the directory may not be empty, and (2) the entity may not be a directory'. Consider the first case of trying to delete the

nonempty

director}' '"foo"":

localhost> rmdir Misc/foo rmdir: remove Misc/foo: Directory not empty-

In this

when

example, the directory "foo" has

command

the

to

remove

issued.

it is

at least

one

The following

file

remaining

action

in

it

taken:

is

localhost> rm Misc/f oo/f ooblah remove Misc/foo/f ooblah? y

rm:

here

rm has been aliased to

'rm -i." meaning interrogate the user before per-

forming the action, and the user provides an affirmative response rm, mv. and

cp

gates the user

(file

(i.e..

asks for verification) before executing the

can be useful when deleting or replacing

chance

to think

'rm - i

'

if

is

used

Chapter to

It

because

Many

should be noted that the

it

it is

5.

users simply alias

rm command is many

file

consider the second case, where the

rm to

actually

institutions,

aliased to the interrogative version for this reason.

Now

remove a

command. This

gives you a second

not used with the interrogative option, and at

including ours, that in

files

over what you are going to do.

in their login shell.

dangerous

to the query,

copy), can each be used with a *-i" option that interro-

More on

command rmdir

instead of a director}

localhost> rmdir Misc/foo/fooblah rmdir: Misc/f oc f ooblah: Not a directory

where the correct action

rmdir on

1.

The

string.

asterisk

is

a

to take

is

to use the

rm command on

files

or to issue

a directory.

nanx completion argument

in regular

expressions that matches an\ character

For more information on regular expressions see Chapter

12.

3.5 Files

3.5

Files

and

File own

file

important

is

tion,

we

ries.

That

files.

look is.

UNIX

the

file

system

system within the global

navigate through the zation

File

81

Manipulation

Manipulation

The organization of of your

and

is

at the

file

that

our use of the computer

manipulation of

files in the

to create,

is

the organization

is

system, and so

system. However, the reason that

every user must be able

The commands

important, as

is

file

is

file

based on

same manner

your

ability to

system organi-

files. In this

sec-

as with directo-

rename, relocate, and remove

for these tasks will be presented in reverse order to the

presentation of directory manipulation, because the last example presented for

removing directories can also be applied File

to file removal:

removal

File relocation

File

renaming

File

copy

Locating

files

Looking

at file

Locating

commands

File

3.5.1

As

a user,

ry.

You

contents

Removal

you will constantly be adding and removing files from your directoadd files by editing new files, saving edited files with new names, and directing the output of programs to new files. We have not covered any of these items yet. To remove a file, however, you will use the rm command, rm stands for remove, and can be used to eliminate single files or entire directories. For example, suppose that, instead of moving the contents of the directory "C-bin" to the directory named "bin." above, you wanted to delete the files and the directory altogether. You could use the rm command first on the files, and then remove the directory with rmdir. as follows: will

localhost> cd -/bin localhost> rm C-bin/* localhost> rmdir C-bin

Again,

we have used

the wildcard (*) to denote

directory. Alternatively, there

contents of

mand

C-bin

is

an

rm

and the directory

will be issued,

all

itself.

Recursively means that the com-

by the system, on the contents of C-bin, and,

the contents are directories, on them, and so forth until the

executed on every directory and issued as

shown subsequently.

file

"C-bin"

items in the

option that recursively removes the

beneath

C-bin. The

if

command

option

is

some of

has been

'-r' and

is

82

Chapter 3 The UNIX

localhost>

nti

File

System

-r C-bin

The recursive option cp and mv. File

3.5.2 File

the

number of commands,

particularly

Renaming

renaming

identical to directory renaming.

is

mv command,

get 1"

available on a

is

"widget"

such as

You can rename

in the directory

jhodges

a

file

to

with

"wid-

as follows:

localhost> mv widget widgetl

It

should be noted

no longer

you now now do

a directory listing,

"widget"

"widgetl."

File Relocation

3.5.3

File relocation is

that, if

exists except as

also identical to directory relocation. If the second argument

is

a directory, then the

new name, then with a new name, a

ties is illustrated

moved

file is

the file

is

then the

to the directory. If the

renamed.

file is

If the

second argument

second argument

moved and renamed. Each

is

is

a path ending

of these possibili-

below:

localhost> mv widget bin localhost> mv widget bin/widgetl

named widget is moved to the bin directory. named widget is moved to the bin directory and

In the first case, the file

In the

second case, the

renamed

to

relocation

with the

mv

widgetl.

that if

new

Finally, the

ment

It

Like the

mv command

in a list

files

rm command, mv

will first ask the user if

its

is

has an interrogative option

(i.e.,

he wants to overwrite the existing If the last

file.

argu-

a directory, then all of the items but the last are

named by

the

last.

The arguments can be a mixture to rename many files

and directories. This mechanism cannot be used

and directories, however.

file

contents will be overwritten

can have more than two arguments.

of arguments

relocated to the directory

of

should be noted, in the cases of file renaming and

the second file already exists,

file.

-i) which

file

3.5 Files

3.5.4

is

performed with the

83

Manipulation

cp command, which

and a new name. For example,

a file to be copied

widget

File

Copy

File

copying

File

and

and then

if

takes

you wanted

two arguments: to copy the file

one of the copies, you could type the following:

edit

localhost> cp widget widget-new

Now you would have names, and you could

two

about loss of the original

moving let's

copy

the

if

files

edit the

with the same contents, only with different

"widget -new"

one named

file's contents. File

the second

argument

is

without worrying

copy also performs the task of

a path and a name. For example,

widget and edit the copy in the directory directory new-files exists, you could type

say that you want to copy

"new-files." Given

that the

the following:

localhost> cp widget new-files/widget-new t

new name

directory

In this case,

widget

continues to exist in the current directory, and a

widget -new, has been widget-new already existed,

copy of widget, called

created under the

files

directory. If

it

written.

By

new

new-

would have been over-

using the - i option, with cp, you can have the system interrogate '

'

file. It should be noted that, when you you you are experimenting with files, it is generally useful to make a copy of the original before you begin, rename it something obvious like "file, orig,"

are about to

if

copy over another

and then continue. The copy to

command can

also be used to

copy directories and

copy them recursively using the '-r' option.

3.5.5 It is

Locating Files in the File System

not at

name of a

all

uncommon

file

you to forget where you put a file, or to forget the remember something in the file. You still need to before you can execute any commands that use it.

for

but be able to

be able to locate the

file

There are two commands

find and the grep

that

you

will find invaluable in

performing these

grep/fgrep/egrep. Given that you can locate a file, there are often cases when you will want to compare files for their differences. In such cases, you will want to use the command di ff. tasks:

Locating a File by

family:

Name

or Characteristics

Altogether too often you forget where you propriate to file

copy every

file

into

last

saw

a

file.

Because

it

is

not ap-

your home directory, and because your

system could be extensive, you need a

command

that will search

own

any por-

84

Chapter 3 The UNIX

System

File

tion of the file

system and return

UNIX command find command

shown

is

is

match your search criterion. The utility. The syntax for the find

files that

the file-search

next.

find [pathname-list] [expressions] where the "pathname- list" can be one or more paths from which to start the search, and expressions represent the command options. For example, suppose that you have a file in your home directory called "widget." You could

find can

first try to

see

directory.

You would

localhost> find

.

if

locate

are located in

your home

type the following:

-name widget -print

In this example, the dot

which file

widget when you

is

(

the current directory.

.

represents the starting point for the search,

)

The '-name' option

name" You

with the following

is

used to say "look for a

could use regular expressions

in this term,

but wildcards (and any special characters) would have to be escaped. This

means

that a backslash (\)

*widget would

\

bols must be escaped in

command and

that

would have to prefix file which ended

search for any

find

widget).

-name

Special sym-

because they have special meaning within the

meaning has

The '-print' option

the wildcard (e.g., in

to

be ignored to use the symbol as a wildcard.

specifies that any successes to the

find

search should

be displayed with their path from the starting location. The output of this com-

mand

looks as follows:

/widget localhost> .

Note directory.

that the path is

Now

Change your

" .

/,"

meaning

that

widget was found

in the current

try the

same command.

directory to the root directory and execute the

find command

try to

move

to another location

and

again:

localhost> find

.

-name \*widget -print

/usr/cpl/aday > find cannot open < /usr/cpl/tests2 > find cannot open < /usr/cpl/vba!077 > find cannot open < /usr/f 1/ jhodges/widget /usr/f 1/moortgat/bin find cannot open < /usr/f 1/swilson/Mail find cannot open < /usr/f 2/ghammer > find cannot open < .

.

.

(T)

.

>

.

>

.

3.5 Files

The ries are

we

file

are looking for

flagged by find.

the root directory. Also,

readable

(i.e.,

path of the

You can

/

noted with

Be prepared

you

will see

(1).

to wait a

while

file is

85

Manipulation

File

Note

that unreadable directoif

you

find from

try a

"cannot open" messages

you do not have read permissions)

directory.

Note

for any unthat the full

was the root directory. same command without having to change directories, UNIX commands, will allow an absolute path.

given, because the starting location

also issue the

because find,

localhost> find

is

and

like all

-name \*widget -print

One

somewhat more elaborate example,

final,

is

find to

to use

search for

meet different criteria. To do so, you must be able to select an item that meets consecutive criterion (logical AND), and you must be able to select an item that meets one or more in a grouping of criterion (logical OR). In files that

find, unless otherwise

stated, all criteria

you provide

for item selection are

considered as conjunctive. This means that the item must satisfy

all

the crite-

(AND). To select one of many, you have to use some roundabout methods, as shown below. Also, I have been using the -print option, but, in this next example. I will delete any files that are located in the " / tmp" directory and are owned by the user jhodges. To do so, I must be able to execute a command rion

on the selected

localhost> find /tmp

set

of items:

-user jhodges -atime

\(

In this example, the f

-o -mtime 2 \)

!2

ind command is

the user has perhaps been putting

some work

porary directory that he wants to delete.

match the

issued on the

"

-exec rm

/

tmp"

{}

directory, so

in the publically available

When you want

\;

tem-

to select items that

logical value (true or false) of an expression, then

you should en-

close that expression in parentheses, but you must escape the parentheses as

have shown above.

I

have used the "-atime" option with a value of

" !

I

2" to

which have not been accessed in 2 days. I have also used the "-mtime" option to select items that have been modified in the last "2" indicate that any files

days.

Any

files that satisfy (i.e..

o" option, for OR), sion.

I

AND are owned by

have then used the "-exec" option

mand. The the

match) one of these two criterion (using the "-

-exec

"

} {

"

expand

jhodges,

satisfy the overall expres-

to delete the files with the

"rm" com-

to the current directory so that the items are found,

option must be terminated with an escaped semicolon (\

; ).

and

86

Chapter 3 The UNIX

System

File

There are many additional options for find, as detailed below:

Table 3.3:

find Options

reference

NAME matches the current filename

-name NAME

True

if

-perm XYZ

»

True

if the file

permission flags match the octal number

XYZ precise-

iy

FOO

-user F00

True

if

the file belongs to

-group GRP

True

if

the file belongs to the group

-atime AT

True

if the file

-mtime MT

True

if

the file has

been modified

-type TYP

True

if

the item

the

rectory

is

d.

has been accessed in

is

and a link

same type is

in

as

GRP

AT days

MT days TYP:

a file.

f. is

the default, a di-

1

-print

Always

true: display the current

pathname

-Is

Always

true; display the current

pathname and associated

-exec

statistices

Execute the following command and string: must be terminated with an escaped semicolon (:) for example.

—

find removes

Used

all files

-name foo -exec rm

.

below

.

{}

\;

named foo

to construct expressions using disjunction

Locating Files by Content The use of find requires that at least part of the original file's name be remembered. When you cannot remember any part of the name of a file, it is not prudent to try repeatedly with various different names simply because the find command is dreadfully inefficient. Instead, you can use a string search command, egrep. grep, or f grep to find the contents of a file. All three utilities let the user find strings within files without knowing the name of the file, and without editing the file. The difference between the grep famil) of

how much versatility matched, egrep allows the

commands to be

is

wait on discussing sions,

it

until

the

Chapter

and f grep requires fixed

command

use of 12.

full

allows

in

defining the pattern

regular expressions, so

grep grep

strings, f

The S) max tor the use of same. They all require a pattern

is

the fastest, and

egrep

commands show n

these

fgrep)

to search for

the

will

allows limited regular expres-

potentially quite slow. is

we

(

and

at least

\\

is

uh

one

3.5 Files

location to look for the pattern

(i.e..

and

File

Manipulation

87

two arguments):

fgrep [options] expression [files] where the "options"

are tabulated below, the

"expression"

is

expression including the string desired (or a string with fgrep). and a

is

of

list

"widget"

you wish

files

to search.

a regular

"files"

For example, consider the fragment of

below:

localhost> fgrep always widget The questions *always* expect the shortest answer. If there is a

fgrep

returns the string

if

Most often you use fgrep on

the file

all

name

is

given. This

the files in a directory,

is

a trivial case.

and sometimes even

multiple directories. In these cases, both the path and filename, followed by the

content of the line in which the string occurs, are

you

are looking for a function definition for

You

rectory.

could

the the file path

list

and

listed.

For example, suppose

"md create" :

line in

which

in a

program

di-

the string appears as

follows:

localhost> pwd /usr / f 1 / j hodges /code / c 1 / S IMULATOR localhost> fgrep md: create */*.cl

rep/demon-processes t (set *ep* (md: create '*ep*)) rep/plnew. t (set *ep* (md:create '*ep*)) rep/p2new. t (set *ep* (md: create '*ep*)) rep/processesl t (set *ep* (md: create **ep*)) rep/processes2 t (set *ep* (md: create '*ep*)) utils/fixmd. t (define (md:create name) find: cannot open < /usr/f2/ghammer > .

:

;

:

;

.

:

;

.

:

;

:

;

.

:

.

In this case,

fgrep

is

being applied to two directory levels (*/*), using

"md: create" in all the below files ending with "SIMULATOR." Each recl" in all the directories sult is written on a separate line, with the path to the file first and the context (i.e.. the line in the file) in which the string is found on the right

the asterisk wildcard,

so

it

will search for the string

"

.

1

.

Note

sions.

that the use of the asterisk as a

The wildcard can be used

in

wildcard

fgrep

in

UNIX

is

different

from

its

use in regular expres-

even though other regular expression operators cannot.

88

Chapter 3 The UNIX

Table

System

File

grep/f grep/egrep Options

3.4:

reference

-X

Display only lines exactly matched (f grep only)

-c

Display only a count of matching lines

-V

Display

-i

Ignore uppercase and lowercase distinction during comparisons

-1

List only

-n

Precede each line by

Some

all

lines that

don't match

names of files with matching its

of the character options for using

relative line

grep/egrep

number

are

grep/egrep Regular expression

Table 3.5:

lines in the file

shown below:

operators

A

Matches

the beginning of a line

$

Matches

the

•

Matches any character

*

Matches zero or more regular expression instances

+

Matches one or more regular expression instances

Comparing Whenever

Files

a data or source

file is

which.

file is

used regularly,

made, and the user

One way

what has changed, only compare files by content, and is the user

command

syntax

is

it

will

is

often the case that modi-

want

to

check on which ver-

to keep track of versions

modification date (see long directory

changes. The

line

by Content

fications to the file will be

sion of the

end of a

that

is

through the

file's

but this mechanism will not tell The dif f command is used to means to locate and keep track of

listing), it

has.

a useful

as follows:

diff [options] filel file2 where "f ile2" can be a directory, or both "filel" and "f ile2" can be directories. In the case where filel and f ile2 are both regular files, the) arc

3.5 Files

and

File

89

Manipulation

compared line by line, and the lines where they differ are displayed. In the case where f ile2 is a directory, f ilel is compared with a like-named file in the directory named by file2. In the case where both filel and file2 are directory names, then

dif f

dif f that

and then

will first sort the directories alphabetically

do a content comparison on each

file.

displays are fairly simple to read.

A block of lines will be taken and

block of line numbers will be displayed. Then the lines

in

filel

will be

Then a dashed line will be displayed, followed by the corresponding lines in f ile2. preceded by a right angle bracket > Below is an example on two short sample files (which are comdisplayed, preceded by a

left

angle bracket ( diff filediffl filediff2 line numbers 2c2,3 -* < that block of line numbers will be displayed. Then the lines in filel will -*

separator

> >

that block of LINE numbers will be displayed. Then the lines in filel will

In the line

number reference of the

display response, the line number range separated by a "c." In the example, the first "2" refers to the line

in

each

in

filediffl.

file is

the options to the

while the "2,3" refers to the lines in f iledif f 2.

diff command

a suitable reference or the

Table 3.6:

diff Options

man

are tabulated below.

in

pages.:

reference

-b

Ignores trailing blanks and strings of blanks

-i

Ignores the case of letters ("A' will be equivalent to 'a'

-w

Ignores whitespace such as blanks and tabs equivalent to 'if (a==b)

3.5.6

A few of

More can be found

.

"if

(

a == b

) '

will

be

Displaying File Contents

at the contents of a file is often enough to tell whether it is the you are looking for. You can use grep or f grep if you remember the contents of a file. However, if you do not remember the name or the contents,

Taking a look file

then you need tents of files.

some general

Both

more

(i.e..

and

cat

brute force)

mechanism

can be used to display

for listing the con-

file

contents.

90

Chapter 3 The UNIX

File

System

Listing a File to Standard

Output by Page

more is a command that takes a file (or list of files) as its argument(s) the contents of the file at the standard output, and

more

displays one screenful at a time. For

characteristics (as described in Chapter 5,

more

is

called a

to function properly, the terminal

page 143) must be

displays a page on the screen, and then asks the user

desired.

You can

, or you can play one

file at

continue to page through the exit

by typing a

'q.'

When

and lists pager because it

a

file

by

file list is

if

set correctly.

more display

given,

more

is

key

hitting the space

will dis-

a time.

localhost> more ftp. list

more

supports

string with the (/)

some

you are looking for a then you could do a search using slash

string search capabilities. If

word "examples"

in

it,

followed by a regular expression for the desired

string:

/examples

and

more would

search for the next occurrence of

place that line near the top of the current screen.

localhost> grep mdrcreate */*.cl

I

|

is

too long to

in the file

can also use

when a directory show on one page:

a process pipe (see Chapter 5, page 159)

UNIX command output

examples

You

more

listing or other

more

have not shown the output for these commands simply because

of output has been

shown

in

Table

3.7.

and

with

shown

already.

Some

useful options for using

this type

more

are

3.5 Files

Table 3.7:

more Options

-n

Specifies

-d

The user quit" at 'h'

and

Manipulation

File

91

reference

how many

lines to display per

page

be prompted with the message "Press space to continue, 'q' to the end of each screenful; illegal user input is responded to with "Press will

for instructions"

number N

+N

Starts the display at line

+ /RE

Starts the display

iN

Continue but redefine the page size

is

Skip forward i lines and continue

if

Skip forward i pages and continue

ib

Skip backward i pages and continue

two

lines

above the

a file

a

then you might simply

file,

is

short or

to

be

N

RE

lines

Output

Listing a File to Standard

When

line containing the regular expression

you do not

really care to look closely at the contents of

dump

the contents of the file to the screen using

cat. cat can be used the same way as more:

localhost> cat .login

This turn the files,

command will scroll through the entire contents of " login" and reuser to the command line, cat can be used very effectively on short .

because

on larger

Two

files

it

quickly shows an entire

unless

it is

used with a

additional programs,

tions of a file or

head

file,

but should be used with caution

command

like

head

or

and tail, can be used

command response. For example,

tail. to display por-

consider the following com-

mand: localhost> tail ftp. list

which would display the started at

any location

ginning of the

file

last

in the

10 lines of the file,

and

or the end of the

it

file.

file

"ftp list." tail can be .

can be started with respect to the be-

92

Chapter 3 The UNIX

File

System

localhost> tail +20 ftp. list

will start displaying lines 2

mand been the

file.

lines

Other options are available, see (man

performs a similar function on the tion

first

"count"

specified, the first

is

from the beginning of the

file.

Had the com-

issued with a -2 0, the display would have begun from the end of

tail). The

10 lines of a

file or, if

head command the

"count" op-

lines.

localhost> head -20 ftp. list

Locating

3.5.7

Commands and Documentation

Sometimes it is difficult to find where a command or executable file resides. If you cannot find a command, then you cannot execute it, because it must be in your current directory,

you

to execute

in

your execution path, or linked

There are two commands

it.

or information relating to

to

your directory for

commands commands whose name you know: which and that are

used to locate

whereis. Locating a Program File The which command

is

used

(in the

C

shell) to find

execution path, and can be useful in determining a particular

name

command command is

exist, to the

the

and what

exist

that is

their ordering

is.

program

how many

files

within your

executable

which traces aliases,

executed with the alias

is

files if

of

they

invoked. The syntax for

which filename and an example

is

shown below

localhost> which tex /usr/f 1/ jhciges/TeX3 0/usr/ local /bin /tex .

In this response, the path

argument identify

is

displayed,

which executable

command

behavior.

of the

which is

first

executable found which matches the

can be used, along with the path variable, to

being invoked

when you

get bizarre

program or

3.6 Filesystem Security

Locating a Program Source or The where is command is used to same way that which is used, but and can be used

in either

low, although usually the

command command

Man

Page

find source, binary, and is

manual

files in the

not limited to the user's execution path

shell. is

93

The command syntax is shown file name alone:

be-

issued with the

whereis [-sbm] filename "

sbm]

where the

first field

als alone.

There are other option

[

" is

(man whereis). Consider

used to search for sources, binaries, or manufields, that

the use of

can be looked up

whereis

in the

man page

on the previous example:

localhost> whereis tex /usr/bin/tex /usr/lib/tex

tex:

Notice that the locations of both the executable and

by whereis. and not searched,

its

source

files is

given

that the previous directory, in the user's execution path,

whereis

was

only looks in standard directories for items.

3.6 Filesystem Security The or

last section

system.

file

of this chapter

When

the 'Is

concerned with the security of your directory -1' command was demonstrated, the first few

is

columns contained several items whose descriptions were These items addressed the permissions and ownership of

left

unexplained.

a directory or the

items in the directory. As a user, you own your own directory. This means that you control who can search your directory, who owns the files or subdirectories in your directory, and who can read, write, or execute files within your directory. It is important that every user be aware of the commands that control access to their directory, and what access control means. In this section, you will learn how to maintain and modify your file system. In particular, the fol-

lowing topics will be addressed: •

Account access

•

Access permissions

•

Ownership

•

Director)'

and

file

creation

masks

94

Chapter 3 The UNIX

File

System

Account Access

3.6.1

The introductory chapter of this manual introduced you control mechanism you have available. If someone is your

rights to

files,

to the

primary access

trying to obtain full

then they must obtain your password. If you regularly

change your password with passwd. then the chance of account break-ins dramatically reduced.

is

important that you not choose passwords that are re-

It is

remember, because they are the easiest codes to break. Passwords same as your name, passwords with a small number of characters, and passwords with commonly used terms, products, and famous people or places are generally considered easy to break. You can selectively allow owner access to your account without revealing your password. You do this by adding machine/name pairs to a file called " rhosts." This will be discussed more ally easy to that are the

.

in

Chapter

cause

it

count

full

7.

page 249. but the

potentially allows

.

rhosts

file is

considered a security risk be-

someone who has compromised another usefs

ac-

access to yours.

Access Permissions

3.6.2

The type of access

that a user has to a file or directory

cess permissions associated with a

can type the 'Is

-1' for a

file

is

determined by the ac-

To see what permissions

file.

a

file has.

you

or directory, as follows:

localhost> Is -1 total 356 -rwx

1

-rw-r— r--

1

drwxr-xr-x -rwx -rwx

2 1 1

jhodges jhodges jhodges jhodges jhodges

656 482 1024 2693 57979

Mar 4 15:05 Jun 17 18:25 Jun 20 10:19 Jul 14 15:10 Jun 8 16:59

testl.c texput.log tmac widget widgetl

(D

L permissions

owner

The

resulting long file and directory listing follows the following format:

[PERMISSIONS] [LINKS] [OWNER] [SIZE (BYTES

The

)

]

[

REVISION -DATE] [NAME]

The permissions of the partial listing are shown in first column identifies the type of permission of an

tifies the tities the

three

item as a

file,

the first ten columns.

a "d" identifies the item as a director]

item as a link.

The next nine columns

columns each. Each

set

in

.

hyphen iden-

and an

1" iden-

are divided into three sets of

stands for one of three user

and other. Permissions are always written

A

item:

t\

pes:

owner, group.

order of owner, group, and other.

95

3.6 Filesystem Security

The

fourth field in the listing identifies the

owner of

a

file

or directory, and

only that user (or a system administrator) can modify the permissions on the item.

Three types of permissions are available: read, write, and execute. Like the user types, permission types are always written in the

same

read, write, ex-

Read permission comes first and is indicated with an "r." An r in column of a set means that this user type (i.e.. owner, group, or other) has permission to read the file or directory. Write permission comes next and is indicated with a "w." A w in the second column of a set means that this user type has permission to write to. modify, or remove the file or directory. Finally, execute permission is indicated with an "x." An x in the third column of a set means that this user type has permission to execute the file or directory. Write permission on a directory means that the user type can create and delete dirececute order. the first

and items

tories

means

designated directory. Execute permissions for a directory

in a

that a user type

directory.

According

list

the contents of or change to the location of the

to this notation, the

owner has

a directory, the else has read

can

read, write,

and execute permission.

item labeled "tmac." above

When

a field in any set

with a hyphen), access permissions of that type

filled

(at 1). is

and execute permission, and everyone

is

is

empty

(i.e..

denied for that entity.

example above, the owner has full permissions on the files "test 1 c." "widget." and "widget 1." but has closed out all access to other users, because no entries exist in any columns after those for the owner. In the

.

Changing Access Permissions or directory. As owner you can change access permissions. The command to do so is chmod. which means "change the mode of a file." chmod can be issued with

There are two ways of a

to

modify the permissions on a

file,

mnemonic (symbolic)

Symbolic With

the

File

or binary arguments.

Mode Change

mnemonic arguments,

a "u"

the group, an "o" for other users, is

file

used

to

add a permission and a

used to designate the owner, a "g" for

is

and an "-"

is

"a" is

used to indicate

all

users.

A

"+"

used to remove permission. For exam-

ple:

localhost> chmod g-rwx,o-rwx tmac

will

remove

users.

all

permissions to the directory "tmac" for

all

"group" and "other"

96

Chapter 3 The UNIX

Binary

File

File

System

Mode Change

Alternatively, a binary shorthand can also be used with this

works,

we

need a brief digression

will

Binary (base 2)

is

we count

using only the digits

numbers

are very popular

used

ing or

in

in

reach 9,

we 1

decimal,

1,

how

and

1

we

first

,9.

.

In binary,

Decimal

10 fingers. Binary

can indicate that electric current

To

and cycle through the

begin with

second column

..

(to the left).

(rightmost)

first

When we

two columns and put

a

1

is

flow-

write the natural

When we

digits.

column

we

reach 99.

in the third

and

at

represent

column

(to the

and so on.

In binary, to represent the natural

through the at

using the digits 0,1,2,

called bits for "binary digits.*'

represent 10 by restarting the

in the

100 by restarting the left),

and

among humans because we have

computers because

numbers place a

we count

not flowing, or the direction of a magnetic field.

is

see

an alternative way, to the decimal (base 10) way, of rep-

resenting numbers. In decimal,

is

chmod. To

about binary numbers.

to talk

bits.

and place a

When we reach 1

in the

1

,

we

numbers, we begin with

0.

represent 2 by restarting the

second column

(i.e.,

2 =

10).

When we

then cycle

first

column

reach 7,

we

two columns and put a 1 in the third column (i.e., 8 = 100). and so on. The same can be done with the octal (base 8) and hexadecimal (base 16) numbering systems. In the octal system, we begin with and cycle through the digits until we reach 7. Using these schemes, we have the following representation of decimal, binary and octal numbers (Table 3.8). represent 8 by restarting the

first

3.6 Filesystem Security

Decimal, binary, and octal equivalents

Table 3.8:

Binary

Decimal

r used for permissions

V^

l

1

2

10

2

3

11

3

4

100

4

5

101

w

5

(T)

6

110

7

111

7

8

1000

10

9

1001

11

10

1010

12

11

13

12

1011 1100

13

1101

15

14

1110

16

15

1111

17

16

10000

20

set

6

14

permissions are grouped into three sets of

earlier, the

Each permission within a 1

Octal

l

As mentioned a

97

may

be thought of as a

3.

(permission denied) or

(permission granted). For example, "r-x" would be 101 in binary and

equivalent to 5 in decimal and octal (noted

used with

chmod

at 1).

This octal/binary code can be

to set permissions. For example:

localhost> chmod 750 filename

would

set the

permissions

to:

rwxr-x

which breaks down

to the binary

and octal representations as follows:

owner:

111

7

group:

101

5

other:

000

The first set (owner) is given the permission to read, write, and execute. The second set (group) is given permission to read and execute, and everyone else (other) has

ships sions,

no permissions

between type,

level,

at all. Fig. 3.2

graphically depicts the relation-

and numerical representations for 744

which give the owner

full rights,

and anyone else read

file

rights.

permis-

98

Chapter 3 The UNIX

Figure 3.2:

7

4

111 10

10

w x

Own

System

Octal and binary codes for

4

r

File

r -

- r

Grp

file

permissions

OCTAL

BINARY

-

TYPE

-

Oth

LEVEL

Below is a session where the permissions on the file "blah" are modified "group" and "other" through their possible values. Note the sequencing of UNIX commands using semicolon. Also note the use of wildcards in re-executing previous commands with minor modifications. The listing is perfor

formed using the

'1'

sions change and

how

that the

it is

localhost> Is -IF blah -rw-r--r— 1 jhodges 44 Jul li localhost> chmod 700 blah; Is -rwx 1 jhodges 44 Jul li localhost> chmod 711 blah; Is -rwx— x--x 1 jhodges 44 Jul li localhost> chmod 722 blah; Is -rwx—w w- 1 jhodges 44 Jul li localhost> chmod 733 blah; Is -rwx-wx-wx 1 jhodges 44 Jul li localhost> chmod 744 blah; Is -rwxr r-- 1 jhodges 44 Jul li localhost> chmod 7 55 blah; Is -rwxr— xr-x 1 jhodges 44 Jul U localhost> chmod 7 66 blah; Is -rwxrw— rw— 1 jhodges 44 Jul U localhost> chmod 777 blah; Is -rwx rwx rwx 1 jhodges 44 Jul li

—

—

File

rights,

an executable

When

an asterisk

is

all

placed on the listing of the

file

and Directory Ownership the permissions

column

in a

in the

directory

'Is

in this

-1'

listing tells

how

manual. The third col-

who the item's owner is. In the example providare owned by "jhodges." If enabled, an owner

the response identifies

items

permis-

file.

links the item has but will not be discussed

ed,

how

permissions are changed so

13:46 blah -IF blah 13:46 blah* -IF blah 13:46 blah* -IF blah 13:46 blah* -IF blah 13:46 blah* -IF blah 13:46 blah* -IF blah 13:46 blah* -IF blah 13:46 blah* -IF blah 13:46 blah*

The column following

many umn in

'F' options so that the reader will see

the display changes.

owner has execute

whether or not

3.6.3

and

of a directory or the

file

99

and Sample Quiz Questions

3.7 Exercises

can change the owner of the item

if

they so desire using

chown command. For example, if we want the user "geisman" cd to the "jhodges" directory and modify the file "widget,"

able to

out giving everyone access to the

file,

then

we can

to

be

with-

type the following:

localhost> chown geisman widget

geisman is the user ID and widget is the item that will this point, geisman owns the file and jhodges does not.

where At

3.6.4

When

a

File

and Directory Creation Masks

new

user account

is

generated, the permissions of directories and files

created by the user have a default setting.

mask, because

be modified.

The

setting

is

called a creation

defines the permissions that users will not be given rather

it

than the other way around (as with chmod. which works after a file exists). As owner of your directory, you can set the default mask at any time using the command umask. The modification of this default, in the login scripts, is part of Chapter 5. umask uses the same permissions encoding scheme as chmod.

except that

it

clears permissions from the full permissions set instead of adding

them from the

null permissions set.

That

is,

the

umask setting is the octal com-

plement of the

chmod

umask

022, which masks out no permissions

value

is

file

permissions created. For example, the default (i.e..

retains all permis-

and masks out write permissions for "group" and "oththey have read and execute permissions). This mask corre-

sions) for the owner,

er" users sponds

(i.e..

to a

755 default permission on user-created

complement of 7

is 0,

and the complement of 5

is

files

and

The number

directories.

2 (based on an octal

system).

3.7

Exercises and Sample Quiz Questions 3.7.1

Exercises

Exercise

1

Exercise 2 Exercise 3

Find the pathname of your

Find the pathname of the

Use Is

to

list

home

directory.

TeX macros

(inputs) directory.

the contents of the directory

"/usr/ local /lib." Try

various Is options (a. la. t. F. R, etc.) and note their effect. Deter-

mine how

to use Is to

list all files

and subdirectories of

all

subdirecto-

ries.

Exercise 4

Create a subdirectory of your naries.*'

1

.

Public execution permission for

Change your

chown

is

home

directory. Call

current directory to be

it

"bin." for

bin.

increasingly being disabled for security reasons.

"'bi-

1

00

Chapter 3 The UNIX

Exercise 5

File

System

Make a copy of "-/ cshrc" in your home directory. Call it "csh. compare." Be very careful not to overwrite the existing " cshrc" file as you are doing this. Ask for help if necessary, but do not let the .

.

person assisting you do the typing. This

is

a normal and necessary task

every user must perform, and you should learn the file

is

in

your directory,

list its

it

permissions.

once and for

all.

Once

Who owns the new file,

and what permissions do they have? Exercise 6

3.7.2

Problem

Change permissions on "csh. compare"

to

-rwx

.

Sample Quiz Problems 1

is the UNIX command to locate and print the names of below your home directory which contain "foobar" names?

What

at

Problem 2

or

What UNIX command(s) would you use

"~/Docs/Letters/TeX"

tory

to recursively

all files

in their

copy the

direc-

"~/Docs/Letters/TeX-

to

Old"? Problem

3

What UNIX command and

Problem 4

is

used to

list

the entire contents of a directory

their attributes (file, directory, etc.)?

What

is

the difference

between

which

and

whereis. Give one

ex-

ample of when each would be used.

Problem

5

What UNIX command

is

used to copy a directory called "dir" and

its

contents?

Problem 6

Suppose your userid

is

vcscl999

and

that

your current working

di-

"-/subdirl " List three ways to change your current directory to your home directory with as few keystrokes as possible. Number your answers from fewest keys to most keys. rectory

Problem

7

Show

.

is

the

UNIX command to change the permissions on

current directory ending with

owner, and read and execute Problem

8

Suppose your userid

UNIX command rectory

to

is

"

.

tex"

to read, write,

all files

Name

"/usr/sl/vcscl999/subl/sub2"

four directories off slash

(/)

is

ending with

your current directory, regardless of where

Problem 9

the

for group, and other.

VCSC1999. What

remove

all files in

and execute for

the simplest/shortest "

.

dvi" from

the di-

without changing from

that is?

and what they are used

for.

Chapter 4 File

Introduction and

4.1

Creation and Editing

Scope

By now you should be familiar with the UNIX file system: its organization, how to move around your directory and other directories, and how to manipulate files and directories. It is now important that you be able to move around within a file and manipulate its contents. By creating and editing files, you can produce programs, program data, and papers. In this chapter, we present two editors: (1) the stock tive

on

UNIX

UNIX editor,

platforms,

vi, and

emacs. Both

(2) a versatile

and popular alterna-

editors are full-screen editors;

howev-

emacs is more extensive and takes longer to learn and master than vi. When you have completed this chapter, you should be comfortable using either er,

editor

on a day-to-day

commands another Ch4

to

file into

opposed

basis. This

move around

the

the current

file,

editing your

own

files will

be

to

being able to enter the editor, use

add or modify

use

commands

to local changes, save the file,

for editing can be found in the

someone

amounts

file,

and

text,

to

move

exit the editor.

"UNIX/Ch4" a much more

text around, read

perform global changes as

Some sample

directory, but

you

files

will find that

valuable experiment than using

else's files.

101

102

Chapter 4

Creation and Editing

File

4.2 File Editing An

editable

file is

a

must be able

the user

to

•

Access the

•

Move around

•

Alter the

file

•

Save the

file

Every

were the

first

screen to display a

4.3

editable

file,

same

will not

an editor which

commands to perform may work on many lines of a

time, but only displays one line at a time. Line

editors developed. Full-screen editors use an entire

file,

and allow the user

to

move around on

the screen as a

modern editors are full-screen editors. The only line this manual is sed. which stands for stream editor.

field. All

editor utility presented in it

To modify an

format.

things:

in the file

A line editor is

two-dimensional

but

1

file

a block) at the

file (i.e.,

do four

ASCII

text editor will provide the user with different

these functions.

editors

written in

file

be introduced

until

Chapter

12.

The vi Full-Screen Editor Of the ed,

editors available, the

mail and is

vi

and easy-to-use full-screen

useful,

now

rn. assume

applications, particularly

We

have a basic working knowledge of vi.

to

it

will

to create a file, edit the file to get acquainted with cursor controls

and moving text around, and then save the

mands

one of the most useful, accept-

Many UNIX

editors.

as the default editor unless otherwise directed, so

even important,

vi

use

vi

(visual) editor is

are tabulated below, but see the

A

file.

few of

man page (man

the essential

com-

vi). or [Joy 1980] for

further details.

File Access: Creation or Editing

4.3.1

Before you

move around

tents of the file.

When

When

or alter a

the file exists, access

to files. In

file,

you must

first

a file does not yet exist, access is

gain access to the conis

called file creation.

called file opening. Every editor provides access

vi. the user accesses a

file

by opening

it

with the vi

command,

as

shown below:

vi [filenamel filename2 ...] means

a file

the top of the file

at

the square brackets,

I.

ASCII

is

an

vi

Opening cursor

acr
,' as shown in Table 5.3:

ps Status swap

Table 5.3:

The

value descriptions

field

w

Process

z

Process that

is

killed but not yet

bl

Process that

is

in

>

Process that has exceeded

is

swapped out

removed

core its

soft limit

third letter of the three to four character status sequence indicates

whether a process

is

nice (man nice). large job to run,

by your work.

CPU

running with altered

Nice

is

used when, for example, you have a particularly

and you lower

In addition,

scheduling priority, using

it is

its

priority so that other users are not

traditional to nice

hampered

your jobs when running them

remotely on someone else's console. As an aside, the use of nice follows:

nice

[

-number

command

]

and

[

arguments

]

usually applied as follows:

is

localhost> nice +10 more Exercise-6 1-output .

have omitted the output because

I

third letter in a process's ' ps uxa SZ USER PID %CPU %MEM jhodges 10067 83..0 0..9 530 vcsc2107 10060 13. .5 0, .2 282 homels32 10054 3, .9 0. 3 245 vcsc2096 10038 3, ,5 0, .9 627 vcsc2095 9561 0..8 0, .2 282 10004 0,.6 0, .2 283 vpcsc4 0.,6 0, ,3 268 pbourne 9160 0,,4 0,,0 6 root 255 78 0, ,3 0, ,1 93 root 8629 0, .3 0, ,3 268 j cheung 8562 0, .3 0,,1 106 root vcsc2185 9195 0, .2 0, ,2 290 vcsc2199 9858 0, .2 0..2 282 8571 root 0, ,2 0, ,1 96 vcsc2109 10040 0,.2 0, ,1 62 62 pbourne 10045 0..2 0..1 3473 oracle 0. .1 0, .8 1792 jhodges 10001 0. .1 0..2 236 vcsc2106 9401 0. .1 0..2 249 shahryar 7153 0. .6 345 .1 jchan 10014 0..3 256 .1 homels32 8428 0. .1 .2 250 root 9222 .0 .1 106 172 fbuenafe 8625 .0 .2 9867 azhao .0 .1 30 root 258 .0 .0 39 daemon 129 .0 .2 123 chance 9814 .0 .2 228 root 111 125 .0 .2 goldstei 7187 189 .0 .3 root 83 .3 145 .0

RSS TT STAT 369 71 119 383

qc p8 pe pc

R S S S

64 pb S 75 qb S

137 q7

I

4

7

S

46

7

s

127 q8 s 34 q7 s 80 q9 s 58 P3 I 40 q8 s 24 pa I 22 q7 I 322 7 s 68 qc s 63 q5 I 262 pO s 118 q4 s

®

TIME COMMAND 0: :00 ps uxa 0: :00 vi lexer. :00 bbs unix :00 emacs list.c 0: :01 vi create. :00 vi cost. mod :03 bbs :48 /etc/update :05 /etc/portmap :01 /usr/ local /bin /bbs :02 telnetd :02 vi dirutil.c :00 vi sos.c :01 rlogind :00 page :00 more -d :09 ora_dbwr_gold :00 -csh (csh) :00 -csh (csh) :08

i2

:00

ftp sfsuvm -csh (csh) telnetd learn sh /etc/cron /etc/syslog -csh (csh) /usr/etc/statd kermit /etc/mountd

pe pd P6 p9

s

:01

s

:03

I

:01

I

:00

7

I

:02

7

I

:04

qa

I

:00

7

s

:00

127 q2 I 105 7 s

:12

95 34 70 29 12 83 64 83

155

:00

®

®

®

Several valuable pieces of information can be gleened from the listing

above.

First,

top (item

note that the

1).

ps

process that generated the listing

Also notice that a user

may have many

is

shown

at the

processes scattered

throughout the table. Notice the variety of tasks the users are working on. and

how many processes are sleeping, how many are idle (e.g., item 2), and how many are running. Often you will want to know which process is most recent, so that you can

kill

the newest or oldest process. Notice (at item 3). that the user

jhodges has a shell process running, and that its PID that the ps command just executed has a PID of 1 67

.

mand must have been

issued after the shell

was

is

10 01. Also note

Because the ps com-

created, this

is

an informal

proof that PIDs increase.

None of this may make

sense

at first,

but

all

of

it is

useful in different con-

1

56

Command

Chapter 5 The UNIX

texts.

One

thing

you can

and you may be able

and Process Control

Shell

right

tell

to tell

how

away

is

whether someone

what they are doing. For example, someone who a file (4)

is

likely to

they are using

is

using

kermit

to transfer

be doing so for some time, but cannot be reached while

kermit.

process hangs,

If the user

was run

then

it

has stopped running and something

can create another shell

in the

background so

ground (see Section

5.3.8,

in

which they can do

that they

page 161), then

its

is

accomplished using the

status

is

to

a

may be wrong.

ps, or

if

ps command

can run a

cumstances, the only thing that can be done This

on the system,

Removing Processes

5.3.3 If a

is

long they might be on the system based on

the process in the fore-

can be known. In

remove, or

kill

many cir-

the process.

kill command. The example below

localhost> kill 10001

numbered 100 01. You need to know the process you wish to kill, which is one of the reasons why the ps command is valuable. Two versions of kill are used regularly. The first kills nicely, meaning it removes the process without doing damage to related processes. The second method is called the "blast" method, because it removes the process without any consideration for the side effects that removal may will terminate the process

number of the job

that

produce. The syntax for each

is

shown below.

localhost> kill pid

or localhost> kill -9 pid

You

should always

method has poor

try to use

are running subprocesses, and

pears to be hung. If a blast all

kill

alone,

(or devastating) side effects.

is

it

may

first,

as

sometimes the blasting

For example, many processes

be one of the parent processes that ap-

issued on this process, then

the child processes as well. This

may

it

will

probably

kill

not be something the user wants and

should be carefully considered. Sometimes a machine will appear to be hung

when

a renegade process

is

really using

up many of its resources, or has created machine, if someone can

a block to further processing. Instead of rebooting the still

login remotely, the offending process might be removed. This could po-

tentially save the

I.

Another

common

work of many users and should always be considered

term for stopped processes

is

wedged.

a

first

157

5.3 Shell Control

line of

defense

in

multi-user systems. Refer to Chapter 7 for the network solu-

tions to this kind of problem.

5.3.4

Process Sequencing

In Chapter 3, the notion of command sequencing was introduced. In UNIX, commands may be sequenced by separating them with semicolons. A common sequenced command is to cd to a directory and then Is its contents. One way is to issue the commands separately, as below.

localhost> cd tmac localhost> Is

However, the same

effect can be realized with a single line, as follows:

localhost> cd tmac; Is Another example

is

moving up

directories using the dot-dot

command

with pwd:

localhost> cd ../..; pwd This example moves up two directories and then displays the

name

of the

directory.

5.3.5

Redirecting Process Input or Output

There are two ways and

(2)

modify the I/O behavior of processes, by ( 1 ) redirection piping. Redirection means that a process takes its input from some to

place other than the standard input

some place

(i.e.,

the keyboard), or sends

other than the standard output

(i.e.,

the screen).

signs are used to perform the redirection. Options are

Table

shown

The in

its

output to

>,

< and >>

Table

5.6:

Process redirection options

5.6:

process




file2

Output

process




file2

process >> £ile2

To

illustrate

to

is

filel

file2

appended

I/O redirection, the

Normally the output from cat

is

filel and to f

output to

file2

ile2

cat command

concatenates two

files.

displayed on the screen (standard output).

By

1

DO

Chapter 5 The UNIX

using the

Command

Shell

> symbol with

and Process Control

a filename, cat can send

its

output to a

file.

localhost> Is -F TeX3 .0/ Texmacros/ bin/ blah localhost> cat blah

>

forward* ftp. list mail -elsewhere/ mail-probs* fooblah; Is -F

texput log tmac/ widget* widgetl* .

®

testl c* texput log tmac/ widget*

fooblah -* forward* ftp. list mail -elsewhere/

TeX3 .0/ Texmacros/ bin/ blah*

.

.

The first listing shows that "fooblah" does not exist. After the redirection to "fooblah," another listing is done, and now fooblah exists (item 1). If fooblah had existed already, then it would be overwritten with the contents of blah. All other lines in fooblah would be lost. An example of limited practical value which you can easily do yourself involves the echo command, which

echo

prints

its

arguments on the screen. Try typing the

command

with the arguments shown below.

localhost> echo my home directory is $home my home directory is /usr/f 1/ jhodges This should display the sentence directly. direct the output to a file called

localhost> echo my home directory is $home localhost> more HOME my home directory is /usr/f 1/ jhodges

If

ing

it

Now

>

you now do an Is on your

directory, the file if

it

mand. This

is

file.

That

is,

very useful

Suppose, for example,

my home directory is $home my user execution path is $path

you cat or

has the sentence

The symbol >> can be used of an existing

to

append

the file will be

when

thing, but re-

HOME

wasn't already there), and,

above, you will see that

do the same

"HOME."

in

the

will exist

file,

as

I

(assum-

have done

it.

the output of a

appended with

creating a small

we wanted

"HOME"

more

file

to create a file with

command

to the

the output of the

end

com-

without using an editor.

two

lines

5.3 Shell Control

where the two values in the

shell variabiles

file.

home

and

path

are

expanded out

159

to their true

This can be accomplished by typing the following:

localhost> echo my home directory is $home > HOME localhosc> echo my execution path is $path >> HOME

and. as before.

HOME

can be

listed to

show

that the

append worked:

localhost> more HOME my home directory is /usr/f 1/ jhodges my execution path is /usr/f 1/ jhodges/bin /usr/ucb /bin /usr/bin /usr/bin/mh /usr/local /usr/local/bin /usr/new /usr/hosts .

Process Redirection and Email Redirection can also be used with the standard

UNIX

mailer

(/usr/ucb/

mail). Suppose you have written a file "myf ile" with your favorite editor and you want to sent the file to a friend, "myf riend." on localhost. Instead of entering the mail environment, you can direct the input to the mail message from the file. Consider the sample scenario below: localhost> mail myfriend


fgrep SDRAW < Lisp/*.cl > items localhost> more items -*- Mode: Lisp; Package: SDRAW -*SDRAW - draws cons cell structures. - draws obj on the terminal (SDRAW obj (SDRAW-LOOP) - puts the use in a read-eval-draw loop in-package SDRAW and lines (vertical). They apply to all versions of SDRAW, SDRAW and subordinate definitions SDRAW-LOOP and subordinate definitions. )

(

"

"

Remember that fgrep matches

string along with

pathnames

their

takes a string and a path and returns each item that

its

end up

will

pathname. In

this

example, the matched lines and

"items." Notice somewhere.

in the file

that

each line

items

file

5.3.6

Piping Process Input or Output to Another Process

Whereas to

has the string

"SDRAW"

in

redirection performs process => file tasks, sometimes

perform process => process

one process directly

tasks.

in the

it

When you want

you

you use a pipe

to the input of another process,

will

want

send the output from

to

).

(

|

Process

piping eliminates the intermediate process of sending the output of the

first

process to the standard output and then using that as the standard input to the

second process. The symbol for a pipe

a vertical bar

take a long directory listing and send

is to

localhost> Is -1

is

it

to

(

). |

A

simple example

more.

more

|

The 'Is -1' command can produce a long directory listing because each is displayed on a line by itself. With many directories, this list may be too

item

long for a single screen display. directly into

step

is

more, you never see

eliminated. There

command,

making

on

no

I

abnormal

piping the output of the 'Is -

the initial listing at

limit to the

make

all,

1 '

command

since the intermediate

number of pipes you can use

in a

sense. For example, years ago (before

used the Troff text formatter. In Troff, there

was

a

I

tbl

pic utility for making figures, an eqn utility for refer utility for making bibliographies. It was not

tables, a

making equations, and at all

is

as long as the pipes

began using LaTeX) utility for

By

a

to take a file

and pipe

it

through

all

of these

utilities,

and then

to a printer.

localhost> troff parse

|

tbl

Although

|

pic

this is

|

eqn

|

refer

|

lpr

obviously an absurd example,

it

illustrates just

how

el fee-

5.3 Shell Control

tive process piping

5.3.7

Splitting

can be.

Output

to Different Locations

There are circumstances where a user send the output of a

command

That way you can see what is

a

may want

to

combine

the effects of pro-

and process-to-process behavior. For example, suppose you want

cess-to-file to

161

UNIX command

called

is

to a file

and

going on, and

to the standard output at once.

later

tee which performs

have

it

to

work

with. There

a branching of output.

copy goes directly to the standard output, whereas the other goes file. One example is shown below.

One

to a specified

localhost> fgrep SDRAW < Lisp/*.cl tee foo -*- Mode: Lisp; Package: SDRAW -*SDRAW - draws cons cell structures. - draws obj on the terminal (SDRAW ob j (SDRAW-LOOP) - puts the use in a read-eval-draw loop (in-package "SDRAW") and lines (vertical) They apply to all versions of SDRAW, SDRAW and subordinate definitions SDRAW-LOOP and subordinate definitions. localhost> more foo -*- Mode: Lisp; Package: SDRAW -*SDRAW - draws cons cell structures. (SDRAW obj) - draws obj on the terminal (SDRAW-LOOP) - puts the use in a read-eval-draw loop in-package SDRAW" and lines (vertical) They apply to all versions of SDRAW, SDRAW and subordinate definitions SDRAW-LOOP and subordinate definitions. localhost> Is CCode pcl-tar-orig. Lisp foo Items descartes pel |

)

.

(

"

.

where our previous example sent the the use of

tee

will also

ticularly useful during

5.3.8

result of the

fgrep

to the file

send the results to the screen. The use of

"items,"

tee

is

par-

debugging.

Process Backgrounding and Multi-Tasking

it be nice if you could perform many tasks at once, even though you may only have one command shell? The utilities that you have been looking at (command sequencing, redirection, and piping) allow a user to perform many

Wouldn"t

tasks with a single line of commands; however, they are put. If a user

wants

to run

many

all

related through out-

"unrelated" tasks, then something else must be

done.

When you

issue

commands

at the shell

prompt, they are run

in the visible

I

62

Chapter 5 The UNIX

Command

Shell

and Process Control

shell or what is called the foreground. Each process must take its turn, because you can only type one thing at the shell prompt at a time. Because the UNIX operating system treats each process uniquely, there is no reason why a process (let's call

it

a job) cannot be

machine when to continue

it

stacked

(i.e.,

put in a queue) and executed by the

has the resources to do so without tying up the user's ability

working.

When

a job

is

stacked,

placed in what

it is

is

called the

background. This "backgrounding" of a process simply means that the system will keep track of the job's progress and notify the user of status changes if desired.

When

a job

is

process and control

placed in the background, a is

new

subshell

is

created for the

returned to the user so they can perform other tasks in

the foreground or parent shell.

When you want to put a process in the background, you type (&) after the command and its arguments, as follows:

an ampersand

localhost> latex Unix-Man & [l] 93 8

-*

[job

number] process ID

The system then returns, as shown above, a job number and a process ID number. To poll the system on the progress of jobs currently running, you can use the jobs command: localhost> jobs [1]938

In this case, there is only one job running in the background and its process ID was "93 8." The system will tabulate the process and provide the user with information on its status. To retrieve the process, one would type

localhost> fg

1

where fg' stands for "foreground," and "1" is the job number. Let's say that you are running a job in the foreground but it turns out to be taking too much time and you have other things to do. In this case, you want to stop running a process in the foreground and put it in the background. This is accomplished '

by typing the following:

localhost> localhost> bg

An

actual

example

is

shown below, where

I

began

to run a latex job.

.

Command

5.4

stopped

and then placed

it.

it

into the

Manipulation

I

63

background.

localhost> latex Unix-Man This is TeX, C Version 3.0 Stopped localhost> bg [1] /usr/f 1/ jhodges/ latex Unix-Man &

where

(~Z) temporarily stops the job. and

'Jbg'

puts

it

into the

commands have the same effect as would '&' upon issuing command. You can see. when the command is pushed into the

background. These the original

background, that

you are creating forking a

this is

what

a subshell in

is

happening.

which

to

When you background

execute the process. This

is

a process, also called

shell, because, in the process hierarchy, the calling shell is a

parent

The number assigned to the subshell is what is returned when you background the process, and you can refer to it with this number, preceded by a percent sign (%). For example, if you decided that you wanted to kill this process, you would either have to do a process listing, find out its PID. and then issue a kill on the PID, or you could type the process, and the subshell

is

a child process.

following:

localhost> kill %1 [1] Terminated latex Unix-Man

5.4

Command

Manipulation many commands

Many

Every user

will issue

commands

issued will be repeated with minor modification, while others

in a

given login session.

be completely identical, differing only by what the current directory

is.

of the

may

There

commands when the system commands you have executed. By manipulating

should be no reason to retype (sometimes long)

keeps a running

commands

Command Command Command

• • •

5.4.1

list

of the

already issued, the user can be

more

efficient.

history repetition

modification

Command

History

make use of previously issued commands, the user must have access commands issued. This is achieved with the history command, history displays a list of the commands issued in the order they were issued at the command line. The shell variable history determines how far back the In order to

to the list of

history

is

retained and can be modified by the user. For example, the following

1

64

Chapter 5 The UNIX

is

1 ocalhost> 1

2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

39 40 41

Command

Shell

and Process Control

a history of a user's session:

history

scan cat login cat .cshrc .

ps ps uxa who rwho -a rwho ruptime Is

more README TeX3 finger jhodges .

.

cat .plan cat project cat .project chfn last jhodges whoami who am i ,

pwd Is

mv blah fooblah Is

mv mkdir Misc mkdir Misc mv fooblah Misc

Is Misc rm -rf Misc history

which shows many of the commands the mistakes,

if

history command

to see

that

you have seen

in this

chapter (even

As a user, you can always issue the what commands you have executed, and then reis-

you can find them

:

-

)

.

sue them or modify them to suit your current activity.

If

your prompt has the

command number in then you may remember, or even see on the screen, the command number. In such cases, the user need not issue the history command unless the desired command is off the screen already.

current

5.4.2

it.

Command

Repetition

The most often-used command modification is to repeat a command. The exis used to repeat a command. The exclamation point is of-

clamation point (!) ten

termed "bang." so the

command

given below might be called "bang 27."

Command

5.4

What follows the exclamation point tells the to

work with

Manipulation

operating system which

(called an event selector). Table 5.7

165

command

shows how event

selection

works:

Table 5.7:

Command

!N

history event selection

Repeat the Nth command;

command N back from

Repeat the

!

string

Repeat the most recent

last

the

command

For example, the following

which was

Is

number

is

preceded by a hyphen, then the is

executed

command

i

i

if

the current position

instance starting with

command

string

will repeat

command number

3 9.

Misc.

localhost> Is Misc Misc: No such file or directory

However, since in

command

that did not

work so well

(the directory

"40"). another example was tried. This time,

had been deleted

command 23 was

reissued.

localhost> !23 Is

forward

new-topics news-groups steph stud212 testl texput log

ftp. list

tmac

mail -elsewhere mail-probs new-net

widget widgetl

F90 Mail

cshrc-cognet dead. letter

Manual -in-LaTeX News README TeX3 TeX3 Texmacros bin blah core

fe

.

filterfile foo2

.

.

Notice that the

oed (item onto

it

.

.

command, as reinterpreted by the operating system, is echThe next step is to repeat a command, but to add

1) before running.

same command reissued example would not suggest it, this

with something else. For instance, below

with another directory after

method

is

®

it.

Although

this

often easier than typing the entire

is

the

command.

166

Chapter 5 The UNIX

localhost> !23 TeX3

Command

Shell

and Process Control

.

Is TeX3.0

README METAFONT README RT README SCORE README. WEB- to-C README WRITE-WHITE README distrib_inf README. vers ion Spiderweb TeXcontrib TeXdoc TeXemacs TeXfonts TeXgraphics TeXmacros aix

BibTeX. inputs COPYING. POLICY CWEB

fontutil make .history makefile makefile. bak mf mfware plain. log site .h site. h. bak stamp-web2c tex texput log texware usr utilityfonts web web2c

.

.

.

ChangeLog.WEB-to-C DVIware Install_INPUTS Install_INPUTS.bak LaTeX LaTeXfonts MACHINES MACHINES tex82 MFcontrib MFdoc MFtexf iles Man-pages PROBLEMS PROJECTS README README APOLLO

.

.

.

.

ams

bibtex cmfonts defaults

.

Notice that

TeX3.0

this

directory

.h

time the effect of the reinterpretation

command, which

is

what

is

listed

on the

is to

execute the

line after the

Is

com-

mand.

Last

5.4.3

Command

Sometimes you change one

will

want

thing, like the

Modification to

do the same operation over and over again, but file. This example was provided in the file

name of a

system security section of Section use of the up carat (~)

which k

will replace

it.

is

used to

3.6.2,

page 94, and

set off the string to

The template

is

is

repeated below. The

be replaced from the string

shown below.

patternl A pattern2 Examples changed

are

shown below, where

to illustrate

how

the access permissions for a file are

they look in a long listing.

5.4

Command

Manipulation

167

localhost> Is -IF blah 1 jhodges 44 Jul 18 13:46 blah -rw-r r localhost> chmod 700 blah; Is -IF blah 1 jhodges 44 Jul 18 13:46 blah* -rwx -* localhost> A 700 A 711 chmod 711 blah; Is -IF blah -rwx--x--x 1 jhodges 44 Jul 18 13:46 blah* localhost> A 711 A 722 chmod 722 blah; Is -IF blah -rwx-w w- 1 jhodges 44 Jul 18 13:46 blah*

——

®

—

command labeled (1). where the 7 00 (orig711 (new permission code) prior to reissuing the command. On the following line, the reinterpreted command is echoed, and then the result of the command is displayed. The same command is performed on the new "most recent" command. You can see that you could The

inal

change

string

permission code)

starts at the

replaced with

is

keep modifying the most recent command.

Command

5.4.4

More

often than not

Substitution

you

will find

minor modifications than

it

to retype

easier to reissue a specific

it.

command

with

you need a com-

In such circumstances,

command and the string modification command, in which you tell the operating system what part of the string to replace. This is accomplished with s." or search and replace command. Below is an example where both are used together. Note the use of two exclamation points ( ).

bination of the repeat

'

:

!

which means re-execute the is

localhoso

!

!

:

last

command.

In this case, the repeated

!

command

!23 TeX3 .0.

s/TeX3 0/tmac .

Is tmac

tmac. Franz

tmac.X tmac.XP tmac Xalg tmac .Xref .acm tmac .Xref ieee .

.

tmac.Xrefs tmac.Xtra tmac.Xtras tmac tmac. an tmac. an. new

tmac tmac tmac tmac tmac tmac

.

This example plished with

mand and last

The

the

i/N

is

TeX3

tA

'

.

.

.

an6n an6t ayday

.bib .

cp

.

.

.

imagen os

.

.

.

.

scover sdisp

tmac tmac tmac tmac tmac

.

.

.

.

.

skeep sref syb vcat vgrind

a bit overdone since the same result could be accomA tmac': however, the ":s" will work on any com.

will only

work on

example, the selection of what selection of

tmac tmac tmac tmac tmac tmac

the to

command argument

ence to the order of arguments.

most recently issued command.

modify was based on

to

In the

a pattern match.

modify can also be made with

refer-

1

DO

Chapter 5 The UNIX

Command

Table 5.8:

and Process Control

Command

modification word selection

Command name

First

argument

(e.g..

$

Last argument

(e.g.,

N

Nth argument

N1-N2

Range of arguments argument

1

The

Shell

' :

A

or

itself (e.g.,

(e.g.,

in the history.

!

:0)

A !

!

!

!

!

•

)

:

:

$)

4)

s' modifier after the event designator

working with commands

!

Below

is

is

(e.g..

!

!

:2-4)

also but one option for

a short reference of alterna-

tive modifiers.

Table 5.9:

Command

:s/patl/pat2

modification reference Replace regular expression

patl

slashes can be replaced by any

:h

Remove

a trailing

:t

Remove

all

:r

Remove

a trailing ".xxx" component, such as ".eps"

but a trailing pathname

(i.e.,

!

!

component

Remove

:g

Perform change globally

:P

For debug; print the modification but do not execute

but the trailing

from "rpO.eps,"

.-r)

:e

all

pat2;

pathname component

leaving the head "rpO"

5.5

with regular expression

symbol

component

it

Linking Files and Directories You have

how to recognize them, how to and how to control them. For each

learned about shells and processes,

customize them,

how

to

keep track of them,

of these, however, the assumption has been

command

made

that

you either have access

would obtain access by placing the proper directory path. Sometimes this can get unwieldy, though, and in your default execution you do not want to keep putting directories into your path. Why? Consider the following example. If someone develops a program that you want to use. then to a

they can

make

or that you

it

read/executable by you. Then, depending on

how deeply

the

5.5 Linking Files

program was nested

in their directory,

path. If they suddenly decided to

move

and Directories 1

69

you would be adding a long item to your the program, your path would no longer

be valid. In general, you do not want to place items in your execution path

which

are not in your

What you do

system.

own

A symbolic link is an

alias,

but

it

is

directories, or in directories higher in the

for the other cases

is

make

UNIX file

a symbolic link.

a pointer to a location in the file system.

A link is

like

a permanent part of your directory rather than something

which is started when you log on. It looks like a file, or a directory, and shows up on a directory listing. The command for creating a symbolic link is In, and the format for creating a symbolic or soft link follows:

In -s original-path your-path where the

's' option

means symbolic, "original -path"

the file or directory, and

"your-path"

directory file system, of the to link to a

program

to retain the

name

the location

is

the true path of

and name, within your

or directory. For example, suppose you want

UNIX directory called "latex,"

in the

in

file

is

your directory.

You

and

that

you want

could do that as follows:

localhost> In -s UNIX/CH6 /LATEX-STUFF/ latex latex

In general, case).

It

you

will

want

to retain the

does not matter whether the original

my

which has

ple,

consider

tial

long listing so that you can see a

directory,

same names

(i.e.,

latex

in this

examnumber of links in it. I will show a parfew such links and what they look like. is

a

file

or a directory. For

a

localhost> Is -1 total 35 -rw-r-r-rw-r-r-rw-r-r-

1 1 1

lrwxr-xr-x lrwxr-xr-x

jhodges 106 Jan 27 21:24 #blah# jhodges Jan 28 22:58 #diss.doc# jhodges 52 Jan 28 22:58 #foo#

1

1

jhodges 27 Nov 7 15:23 dvi2ps -> TeX3 0/usr/local/bin/dvi2ps jhodges 42 Sep 30 17:09 latex -> - jhodges/TeX3 O/usr/local/bin/latex .

.

local name

localhost>

In this example, tor

shows

link,

it

real

path

you can see

the link with an

'

that the first field of the permissions descrip-

1' flag.

displays both the local

real name

When

name and

the listing

shows the full path name.

the real path and

for the

170

Chapter 5 The UNIX

5.6

Exercises and Sample Quiz Questions 5.6.1

Command

Shell

and Process Control

Exercises

Exercise

1

Write a command that will display the message, "These are all the files in the directory ..." along with the list of all the filenames.

Exercise 2

Create two

two

test files

Redo

files.

with a few lines each. Use cat to concatenate the

have the output sent

this but

but this time append a third

Exercise 3

5.6.2

Problem

Run

file to

UNIX commands

a test on one of your

to a third file.

Do it again,

the concatenation of the in the

two

files.

background.

Sample Quiz Questions 1

to make some modifications/customizations to your ".cshrc" login script. Outline how you would go

Suppose you want

".login" about

this

or

and what considerations you should address along the way.

how

Problem 2

Explain

Problem 3

Consider the •

Which

the semicolon

ps is

listing

the

is

used

in

process control.

below and answer the following questions:

most recently used command

•

Explain the status fields of process 59

•

Can you

tell,

from

this table,

which

shell?

shell process

spawned pro-

cess 2608?

USER hodges root root root root root root root hodges hodges hodges root

PID 2630 2543 1

54 59 66 63

2539 2544 2608 93

%CPU %MEM VSIZE RSIZE TT STAT 1.5 1.4 1.34M 400K ql S 1.1 1.27M 312K pO S 0.5 0.0 0.8 1.31M 224K ? S 0.0 0.9 1.24M 256K ? S 0.0 1.4 6.37M 392K ? S N 0.0 1.0 1.25M 288K ? S 0.9 1.23M 248K ? 0.0 S R N 0.0 8.8 14.3M 2.45M ? 1.4 1.34M 392K pO S 0.0 0.0 1.4 1.34M 408K qO S 0.0 1.7 5.56M 480K qO S 344K ? S 0.0 1.2 1.34M

Problem 4

When

is

TIME COMMAND 0:00 -bin/csh (csh) 0:11 layers 0:00 /usr/etc/init -xx 0:00 /usr/etc/syslogd 0:22 /usr/etc/nmserver 0:00 /usr/etc/nibindd 0:05 /usr/etc/portmap 78hr (kernel idle) 0:00 -csh (csh) 0:01 -bin/csh (csh) 0:05 vi Unix-AppA-SF.tex 0:00 /usr/lib/sendmail -bd -qlh

I/O redirection most useful?

When

is

piping most useful? Pro-

vide an example which exemplifies each answer (can be written).

Problem 5

What

is

process backgrounding? Provide an example of stopping

process, backgrounding

it,

checking

its

status,

a

and bringing back into

the foreground.

Problem 6

Explain the use of the

history command

in

performing

command

5.6 Exercises

repetition

and modification. Provide an example of each.

When you

Problem 7

log on to a

der they happen

in,

UNIX

platform, explain what happens, what or-

and why.

Explain what an environment variable

Problem 8

and be

MAIL

What

variables are.

is,

and what the USER,

HOME,

most

likely to

shell are these variables

set in?

What

Problem 9

171

and Sample Quiz Questions

is

a

"command

alias," as

used

at the

command prompt or in the commands and explain

".cshrc?" Give two examples of legal alias

what they do.

Problem 10

Suppose you use the

are logging

vi editor,

on from a

modem

you have a hard time getting out of the most

likely to

home.

at

the backspace and escape characters

be?

List, in

editor.

When you

try to

do not work and

What

is

problem

the

order of priority, the steps you would take to

correct this problem.

Problem

1

1

Your last command was: % chmod 755 f ileA. Show how you would make your next command change permissions to owner read, write,

and execute, only, on a file named "fileB" using

command mod-

ification.

Problem

1

2

The sample process

status listing given

es running on a platform that

your userid

is

by

below

the userid hodges.

hodges, provide (1) a

sleeping processes, (2) give the

lists all

current process-

Assuming

list

for a

moment

the process ids for

UNIX command

to blast

all

one of the

process jobids.

USER hodges hodges hodges hodges hodges hodges hodges hodges hodges hodges

PID 202 216 215 210 208 206 214 211 212 217

%CPU 47.7 44.1 2.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0

%MEM VSIZE RSIZE TT STAT TIME COMMAND 37.4 30. 4M 12. 0M ? R 30:59 - console (WindowServer) 5.4 4.15M 1, 72M ? R N 22 04 /LocalApps /Backspace app/Ba 2:46 / LocalApps /FrameMaker .app/F 15.7 8.61M 5 03M ? S 0:04 /usr/lib/NextStep/Workspace 6.9 5.56M 2 2 0M ? S SW 0:00 (appkitServer) 1.3 2.07M 432K ? 1.6 1.72M 528K ? S 0:00 /usr/etc/pbs -a 0:00 /Next Apps/Edit.app/ Edit -NX 4.2 4.92M 1.36M ? SW 0:00 /NextApps/ Preferences app/P 4.1 5.27M 1.31M ? SW 4.8 3 .88M 1. 52M ? SW 0:01 /Users/hodges/Apps/Date -NX 0:00 -csh (csh) 1.1 1.62M 368K pi S :

.

.

I

#2

5.7

Chapter 5 The UNIX

Command

Shell

and Process Control

Recommended Reading Shells Joy,

W.

[1980].

An

Introduction to the

C Shell, Computer Science

Division,

Department of Electrical Engineering, University of California, Berkeley, November.

6.1

Introduction and One of

Scope

the primary services a

computer provides

the ability to print docu-

is

ments. In this chapter, three techniques are presented for formatting and printing documents. For each, an overview and

along with examples for

its

use.

command

The examples

syntax will be presented,

will be illustrated

on

files

which

you should be able to replicate directly. You will be expected to understand the differences between wordprocessing and text formatting, and to be able to format and print simple documents. A simple document will be a code listing, the documentation for a program

in

manual format, and a simple paper

turning in as a term project. Samples al

examples are provided

in

will be provided

Appendix

L.

We will

and discussed. Addition-

leave up to you the decision

if any. to use on a long-term basis. Specifically, ment preparation techniques will be presented:

of which,

• •

•

suitable for

the following docu-

vgrind nrof f and trof f latex

Within the context of printing documents with a particular package, or a particular fashion,

chapter

is

is

the basic process of printing a

document

at all.

in

This

divided into sections that address the process of printing, and spe-

cialize in later sections to printing with a particular

method,

to achieve a par-

ticular end.

173

1 I *\ Chapter 6 File Formatting and Printing

6.2

Printing Etiquette Printing

is

very important to students in computer science, because programs

cannot always be read and edited (online) effectively. At some point you just

have

code

to see

in print. In the past

decade, the preparation of documents: for

assignments, reports, papers, and publications has also risen steadily. The need

which support all phases of code and document preparation, has become commonplace. Historically, high-speed line printers have been available to print out galleys of programs in draft mode, while dot matrix and laser printers have become available for higher=quality work. Although the trend has been toward higher quality printers, the cost of

for printing diversity, and applications

printing remains relatively high, so

it is

monsense guidelines when you decide •

important to keep in mind a few com-

document.

to print a

Being able to print code and documents

is

a privilege, not a right.

Never

abuse printing privileges with excessive or inconsiderate use. •

If

you need

to print source code, then use a line printer

•

If

you need

to print

vgrind •

Never

(or

print

code on standard-sized paper, say for a

man

on

don't print

it.

Printing large

documents

is

something

like a thesis,

line. In general, if

extremely cycle intensive.

you

are keeping other people

Remember

work, theses, or publications.

that, if

In general,

it is

who

considered in poor

taste,

and. at

ad-

documentation

When you

print out

from finishing home-

everyone thinks only of

themselves, then the network comes to a screeching •

report, then use

pages. System manuals are provided by the people

line,

exists

possible.

equivalent), in landscape format.

its

minister a system and generally exist on

•

whenever

halt.

many

institutions, not al-

lowed, to print online manuals. Before considering printing a manual, consult •

your local administrator and find out what the rules

When

printing a large job

is

justified, print

it

in

chunks rather than

so that other users with smaller jobs can get their •

Print large jobs

•

Text formatting (i.e..

•

nice

when CPU is

are.

cycle intensive. Try to run print jobs on lower priority

them) whenever possible.

Tagged

change Format (TIFF), and Bitmapped screen dumps take up a

lot

Inter-

of space.

takes a laser printer a long time to format pages with graphics. Try to break

up •

once

loads are low.

Pictures, such as PostScript. Ecapsulated PostScript (EPS).

It

all at

work done.

print jobs so that

Whenever you

print a

pages with graphics are printed separately.

and a previewer (when applicable) before save a lot of trees, and it will decrease your

possible, use a speller

document. This

will

edit time. •

When

your document has many figures

that

must be placed, often

efficient to test print the figures separately to

Then,

in the

document, reserve space

make

for figures, tables,

format the document without them until

all

it

is

more

sure the) look right.

and captions, and

figures and tables are correctl)

6.3 Printing Tools

placed.

Then

ing this with

insert

them

latex

into the

document

for printing.

The method

1

75

for do-

will be explained.

The more you work with text formatters and printing on a network, the more these rules will affect you. More often than not, you will be the brunt of someone else's negligence, so the more people who actively adhere to these guidelines, the better off the network community will be.

Printing Tools

6.3

Before a document

is

printed, every user should

ration utilities available to assist in preparing the

Ch6

know of the document prepadocument and using the print-

ing resources wisely. In this section several tools for checking and validating

document before printing will be introduced, along with the print commands The files and test output for these examples can be found in the "print- tools" directory. The following tools can be used to edit an ASCII document before it is formatted or printed, in order to help edit the file and eliminate or reduce excessive printing. For example, when you prepare a document, you always want to check the spelling in it before printing. UNIX has a utility called spell that can be invoked on a file that returns a list of misspelled words. Consider the small document presented below, called "realpaper." a

themselves. print-tools

localhost> cat real-paper Graduating in Four Years: A Forgotten Trust Bachelor O. Science Abstract A decade ago, the promise of a college education in four years was a real expectation for students in american universities. With the advent of

.

.

.

Introduction This year will mark a decade in the information age. And with this age has come a terrifying realization that students cannot hope to assimilate the information required of them in an undergraduate program, and somehow put themselves through school, in a four-year term... The Demise of Student Support for Higher Education The major threat to higher education in the past half decade has been the lack of educational support by the taxpaying public. The effective result is that students are, to an increasing extent, being forced to pay for their own educations. Tie this into increased costs and time to graduation and the result is an ever decreasing number of graduating students The Increase in Required Information

real -paper

represents a simple

ning of a fictitious term paper.

We will

ASCII

file,

what might be the begin-

use this text to illustrate the use of var-

1

#6

Chapter 6

File

Formatting and Printing

ious utilities in the following sections. For example, to run

paper you

localhost> spell real-paper localhost> more rspell american

This

spell on real-

type the following:

>

rspell

command

applies the

results of spell

spell

real -paper and re-

utility to the file

"rpspell." Had

directs the output to the file

the redirection been omitted, the

would have been displayed onscreen.

If the list

of misspelled

words had been long, this might not have been desirable. Note that there is only one mispelled word, "american." which should be "American." In general, the list of mispelled words is given alphabetically, and the correct spellings are not provided. Use

look

for finding possible spelling for

words flagged using

spell. Five additional UNIX utilities which can be used to prepare your document: wc, spell, style, diction, and explain are shown, with their arguments, in Table 6.1.

Table

6.1

:

ASCII

file

checking

utilities

spell FILE

Runs a

wc FILE

Counts words,

look WORD

Looks up

style FILE

Analyzes the readability of your

diction FILE

Looks through

explain PHRASE

Gives thesaurus entries for an awkward

Finding

6.3.1

The look its

spell

lines,

spelling

Word

utility is a

checker on the document

and characters

on

WORD

as

you

FILE FILE

in

spell

them

FILE

the file for outdated and

awkward phrases

PHRASE

Spellings

companion

argument, as you would

spell

to it.

spell, look and finds words

takes a particular

with the assumption that you can recognize which one

when out as

real -paper,

on the misspelled. Running look on

I

ran spell

file

this

the

word

as

that are spelled similarly,

word

word produced

is

correct.

For example,

american was

called

the following response.

6.3 Printing Tools

I

77

localhost> look american American Americana Americanism

Counting Word, Lines, and Characters

6.3.2

The wc program grams,

wc

is

probably used most often of the document preprint pro-

a paper for a class, or for publication, and have a

wc

will

file. When you are preparing word minimum or maximum,

counts characters, words, and lines in a

come

in

handy,

wc

can be invoked as follows:

localhost> wc real-paper 28 156 969 real-paper

column of this output is the number of lines in the file. The second number of words, and the third is the number of characters. Thus, real -paper is a whopping 2 8 lines long.

The

is

first

the the

6.3.3

Checking Document Readability

Although not used as often as spell or wc, the other four

utilities are available

them out. The style function is used to compare the readability of your text. The man page can give more detail, but the essence of the command is to show the approximate reading level of the sentences of the paper, as defined mostly by length and phrase complexity. The figure on the following page is an example of style invoked on real -paper. The display shows five different components: (1) readability grades, (2) sentence info., (3) sentence types. (4) word usage, and (5) sentence beginnings. for those

who wish

to try

In general, as a writer,

you

are trying to maintain the content of

your paper

while lowering the readability ratings (highlighted) of this output. The com-

mon the

belief

is

that the easier

more people who

it

is to

read a document, regardless of the content,

will understand, and. hence, appreciate

what you are

try-

ing to say. Notice that there are four different rating scales provided (Kincaid. auto.

Coleman-Liau. and Flesch), and

ent. In general, scores

that the score

under each scale

under 10 are considered good.

is differ-

1

78

Chapter 6

File

Formatting and Printing

localhost> style real-paper real -paper readability grades: (Kincaid) 15.3 (auto) 15.3 (Coleman-Liau) 12.8 (Flesch) 15.8 (31.5) sentence info: no. sent 6 no. wds 155 av sent leng 25.8 av word leng 5.05 no. questions no. imperatives no. nonfunc wds 87 56.1% av leng 6.78 short sent (36) 17% (1) longest sent 64 wds at sent 3; shortest sent 5 wds at sent 6 sentence types: simple 67% (4) complex 17% (1) compound 17% (1) 0% (0) compound-complex word usage: verb types as % of total verbs tobe 46% (6) aux 31% (4) inf 23% (3) passives as % of non-inf verbs 10% (1) types as % of total prep 14.8% (23) conj 2.6% (4) adv 1.3% (2) noun 29.0% (45) adj 20.6% (32) pron 1.9% (3) nominalizations 4 % (6) sentence beginnings: subject opener: noun (2) pron (0) pos (0) adj (0) art (2) tot 67% prep 17% (1) adv 0% (0) 17% (1) verb 0% (0) sub_conj 0% (0) conj expletives 0% (0)

Sentence

info,

and sentence types are both based on sentence length, while

word usage and sentence beginnings each sentence.

It

on the types of words found

in

Checking Phrase Style

6.3.4

The diction program or outdated. es with

ample

are based

even looks for expletives.

is

used to find phrases which are considered awkward

When executed on

awkward

your

file,

diction produces a listing of sentenc-

phrases, set off by asterisks and brackets

that applies diction to

real -paper

is

*[...]*. An

shown below.

ex-

6.4 Printing a

Document

179

localhost> diction real-paper real-paper Tie this into increased costs and time to graduation and the result is an ever decreasing *[ number of ]* graduating students.

number of sentences 12 number of phrases found

This output means that the phrase

1

"number of "

is

improperly used

in the

context of this sentence. This phrase can then be used as input to explain.

Correcting Phrase Style

6.3.5

The explain program takes phrases indicated as awkward by diction and returns thesaurus entries for the phrase which the author can replace the odd phrase with. The phrase "number of" from real-paper is applied to the explain program below: localhost> explain phrase? number of use "many" for a "a large number of" use "several, many, some" for "a number of" use "usually" for "except in a small number of cases" use "some" for "in a number of cases" use "enough" for "sufficient number of" use "often" for "in a considerable number of cases" phrase? -^

(T)

clear that explain leaves something to be desired, because a better re-

It is

at "is" and would be "fewer graduating students." Nevertheless, the program offers another viewpoint, and that is sometimes valuable. The program will continue to prompt for phrases until you kill the process, as shown at item (1).

placement would begin

6.4

Printing a

Document

Regardless of what means one chooses to print

must know how

to

invoke the printer,

how

to

(e.g.. laser

check the

or line printer), one

print queue,

and

how

remove a print job from the queue. When a document is prepared to a point where editing a hard copy would be useful, the command used to print the doc-

to

lpr. lpr (man lpr stands for "off line print" and has options for which pages to print, how many copies to print, what printer to select printing, and so forth, as described in the manual page. The general format

ument

is

telling

for is

shown below.

)

180

lpr

Chapter 6

[

File

options

Formatting and Printing

[file

]

where some of the "options" from the man page are

"file" Table 6.2:

is

below, and where

listed

the file to print.

lpr CO mmand option reference

-h

Do not print

-in

Indent printed output by n spaces

-Jjob

Print the

-m

Send a mail note

-Pprinter

Send the output

-Ttitle

Print the

-#N

Print

6.4.1

the banner page

argument to

ob"

as the job

you when

to the spool

argument

N copies

j

"

title

name on

the banner

page

the job has been completed

queue

at the

of the specified

by

for the printer specified

printer

head of each page

files

Line Printers

There are generally two types of printers available on a system: draft mode printers

and laser

printers.

The default printer

is

line

usually a line printer, so any

output sent to the printer will be printed on the line printer. The procedure for printing a file

command

on the

line printer is

shown below. Use

the following

UNIX

format:

lpr -J BIN## filename where '-J'

is

printer output. tion is

an

A

lpr

option used to print a banner on the

print banner

and can be anything

that

an example of a banner that

For example,

if

I

type the

is

page of the

simply a large font used for easy identifica-

is

can

first

assist in identifying

your

print job.

used as a sorting mechanism

"BIN##"

at this institution.

command

localhost> lpr -J BIN20 myfile.c

to print a file

named "myfile.c"

mechanism, above, pick up

"BIN20." The

bin

my

to a line printer and.

output

number allows

in the

the person

using the sample

designated location, sorted into

who

sorts the print jobs to split

Document

6.4 Printing a

them ed

into smaller,

more

identifiable bundles. Often print jobs

to a shared printer are sorted

of the user.

You

mechanisms used

should write

name being

which

181

are print-

by the name

by the

file

down

the locations of local printers and the

for sorting jobs here,

printed, or

and on the inside flap of

this

book.

Printer Location Line Printer Name Laser Printer Name

Banner Requirements /Options

6.4.2

Laser Printers

There may also be laser printers available for your use. Please reread the

print-

ing etiquette rules above prior to using a laser printer, because they are expensive

and someone has

mat

as a template for printing

to

pay for them. Use the following

on a

UNIX command for-

laser printer:

lpr -J BIN## -Pprintername filename where the '-P' option

is

being invoked to redirect the output to the printer

named "laser." The naming convention

change from loca-

for printers will

tion to location, but there will

always be a difference

laser printers unless there are

no

line printers.

in the

names of

line

and

The command can be used

in

conjunction with a text formatter and various preprocessors/postprocessors (or filters), as illustrated

below.

localhost> nroff real-paper .troff

In this example, the

per troff" .

When

|

nroff

and the output

document, and then

PostScript

tbl

|

text formatter is

sent into the

tbl

used on the utility to

file

"real-pa-

format tables

in the

to the printer.

your work files,

is

lpr -Plaser

is

PostScript, or includes PostScript or Encapsulated

then you must send your print

file to

a laser printer which sup-

ports PostScript printing. In the preceding example, this

is

why

the '-P' option

was used. 6.4.3

Checking Status of Print Jobs

When you

print a job.

you generally

where

in the stack

of jobs

it is

the status of your job easily

mand. An example

is

(i.e..

like to

know when

it is

done

the queue) waiting to print.

enough with

shown below.

printing, or

You can check

the line printer queue,

lpq com-

1

82

Chapter 6

File

Formatting and Printing

localhost> lpq -Plaser laser is ready and printing via lat Rank Owner Job Files active jhodges 34 um3.ps

The

first

Total Size 2246554 bytes

display column. "Rank." will

with the job which

is

printing on top.

list

the order of jobs in the queue,

The job which

tive." The "Owner" column is the userid that is an identifier, the "Files" column identifies

is

printing

labeled "ac"Job" column

is

sent the job, the the file that

is

printing,

and the

"Total Size" indicates how much space is required to print the job. Notice that um3 .ps, which is the PostScript of the current version of this book, is rather large (2.25

Meg). Normally

this all at once, so

low

to kill

I

it

would be considered

will use the print job

command

poor in

taste to print

an example be-

it.

Removing Print Jobs from

6.4.4

removal

in

the Print

Queue

when printing a job, you may have cause to remove the job from One such case would be if you were demonstrating how to use the printer and the printer status commands, as I am now. More realistically, if you realize that you have made a mistake, or if you change your mind, you might want to cancel the job. One way to gauge a mistake is by the size of the file. If you have a general idea of how large the file should be. then if it is much Occasionally

the print queue.

it might be worthwhile looking at the file. The remove a file from the queue is Iprm. When using the lprm command, you must identify which job to remove, and which printer to remove it from. If you do not, then all your jobs will be removed. An example that removes the job I sent to the printer, shown above, is shown below.

smaller or larger than that size,

command

to

localhost> lprm 34 -Plaser dfA034sfsuvaxl.sfsu.edu dequeued cfA034sfsuvaxl.sfsu.edu dequeued localhost> lpq -Plaser no entries

6.5

Laser Printing

Mode

in Draft

way to print a document is laser used when code is being turned in paper and look good. The utility

After a line printer, the next least expensive draft

mode. Laser

draft

mode

with a report and must be

vgrind file

"f

is

used to send

ilel" and

is

(in

generally

standard

Files to the laser printer.

save the output to a new

file,

For example,

to

vgrind

a

"f ileloutvg." you can type

6.5 Laser Printing in Draft

Mode

183

as follows:

vgrind filel -t

>

This

fileloutvg now creates

such as shown

in the

a PostScript

command

file that

can be sent directly to a laser printer,

below.

localhost> lpr -Plaser -J BIN20 fileloutvg

along with whatever options that are requested. For the case above, the

fileloutvg

will be printed

on a laser

printer.

Some

file

vgrind options

of the

are listed below.

Table 6.3:

vgrind Command option reference

-h HEAD

Causes the output

-1 LANG

Specifies the language, (C,

PASCAL,

to

have

HEAD

LANG,

to use in

choosing printing style

LISP, CSH, SH)

N

-SN

Printing point size given a

-t

Sends output

-W

Forces output to a wide printer

-X

Outputs index

Ch6

printed on every page

to the standard output rather than to

file in

lpr

pretty format

Consider a program

file

named "shortlispf ile.cl," which can be

in the "vgrind" directory. In the example below, the file is printed usvgrind. Because it is a lisp file, the '-1' option '-lisp' has been used 'to format it. Were the file a C program, this same option would have been lc' The '-t' option sends the output to the standard output, which has, in this

found ing

vgrind

example, then been redirected to a to

show you

that the file

an optional header.

is

file

ending with

a PostScript

"MISSIONARIES"

file.

" .

ps." This has been done

The command below

at the

localhost> vgrind -lisp -t -h "MISSIONARIES" shortlispf ile.cl localhost>

The

file

generated in this process,

also prints

top of every page.

vgrind2

.ps.

is

>

vgrind2.ps

shown

in Fig. 6.1.

184

Chapter 6

Figure

6,1

:

A

Formatting and Printing

File

PostScript

generated for laser draft with vgrind

file

shortlispfile.cl

Cannibals and

MISSIONARIES

shortlispfile.cl

Missionaries

There are three functions:

way

invoke

to

(this

depth-first

solution

breadth-first

branch and

the

solution

solution

best-first

missing

is

function

its

(dfs-mandc) (bfs-mandc) (best-mandc)

using

a simple cost

bound search since

I

cannot

function think

of a good heuristic)

A

state

missionaries on

bank,

right

by

represented

is

of cannibals on

the

and

fourth

the

the

bank,

left

numbers. The first number is the number second number is the number of

four

bank,

left

the

third is the number of cannibals on the number of missionaries on the right bank. missionaries on the left and 3 cannibals on

the the

is

For example, (0 3 3 0) means 3 the (3

The

righi.

3

start

therefore

state

3

(0

is

3)

and

the

goal

state

is

0).

Moves

The first number is subtracted from the number of cannibals on the left bank and added to the number on the right bank. The second number is subtracted from the number of missionaries on the left bank and added to the number on the nght bank. All (setq

;

All

(setq

;

are

represented

moves to the *neg-moves*

by

out

the

-!)

moves of

nice-pnnt-mandc

(defun

(null

(if

pair

of numbers.

left.

'((0

moves to the right. *pos-moves* '((0 1)

Print

a

history)

(-1

0)

(-1

(I

1)

0)

(1

the

-1) (-2 0) (0 -2)))

(2

missionaries

(0

0)

2)))

and cannibals problem

in

a

nice

way.

(history)

ni!

(progn (pprint

;

(car

history))

(fresh-line)

(print-statop

(car

history))

(fresh-line)

(nice-print-mandc

;

Print

(defun

the

print-statop

(

C

M

(print-bunch

(wnte-string (cdr

"

(wrile-stnng

(print-bunch

Feb 2 11:58 1992

history)))))

a

pretty

(caar

way.

statop)

(cadar

3)

statop)

3)

")

statop)

(wnte-stnng (pnni-bunch

in

statop)

(pnnt-bunch

(if

(cdr

state-operator

(pnnt-oper (cadr statop)) "

"))

")

"

C

M

(caddr

(car

statop))

(cadddr (car statop))

3)

3))

Pa#c

I

of slwrtlispfile.cl

versus Word Processors

6.6 Text Formatters

6.6 Text Formatters versus A

text formatter or

tained in a text

Word Processors

markup language

file into

185

is

used to organize the material con-

an attractive format similar to what a word processor

does on a personal computer. Text formatters are generally used when draft

mode produces

insufficient quality.

For example, a

a paper, a thesis, a report, an article, and a

uments which can be prepared with

book

letter,

a set of lecture slides,

are increasingly

text formatters. Until

every

complex doc-

UNIX platform

in "What You See is What You Get" document formatters will continue to be valuable tools.

has the ability to display documents

(WYSIWYG) Some

format,

people continue to use text formatters even though they have access to

word processing and page layout applications. Two of the primary reasons for this are: (a) the actual document is an ASCII file, so it is smaller and can be easily sent anywhere (and then recompiled) via email, and (b) the formatting is semantically clear, meaning that the author selects a style and

excellent

it up to the implementation to decide how to interpret that style. One of most popular text formatters today is the Hyper Text Markup Language (HTML), which is used to format documents for the World Wide Web (W3).

leaves the

HTML is used on the Web is that many different types used to interpret a document. HTML specifies the names of

The primary reason of computers are

commands used display text, text will

etc..

to

that

format a document, and suggests

but

it is

to

the local

browser

to

how

the

commands will how the

determine exactly

appear on a particular screen.

A text formatting ments

left to

commands writers use in their docuappearance when the document is later displayed

language

produce the desired

online or printed. All

clicks and

ing of text formatting

a set of

word processing programs use

guage, but generally hide the the like) to

is

commands from

improve user is

a text formatting lan-

the user (with menus,

mouse

friendliness. In this respect, an understand-

extremely useful to anyone

who

is

writing documents

on a computer.

A text formatter is a type of compiler. text,

and those expressions are placed

guage definition. Each formatter has

mat

is

its

It

has expressions which operate on

in the

own

document according

to the lan-

language, but an interchange for-

slowly emerging for transferring documents from one hardware plat-

form, and formatter, to another.

An

interchange format enables the translation

of a document written with one formatter into an application independent

ASCII

Another text formatting language can then be applied to the interchange file, and. whatever commands are supported by the new application will

file.

be translated properly. Those capabilities that are not supported are con-

verted to text.

1

OD

Chapter 6

File

Formatting and Printing

Text Source File

6.6.1

A user begins using a text formatter by creating the text which will be formatted using an editor such as vi. This text file the text

which

will tell the

pared, the text formatting application

new

result is a

called the text source

is

file.

When

commands may be inserted into the document formatter how to format the file. When the document is pre-

written, formatting

is

file

is

invoked

to

compile the document. The

with the interpreted document translated into a form a print-

er can understand.

Sometimes

this stage

can be printed directly, while other

times another program, a translator/converter, will be needed to produce a printable

6.6.2

file.

Features of Text Formatters

Text formatters are generally very

versatile, usually sacrificing user friendli-

ness for the sake of feature versatility and user control.

needed ers

to

produce high quality documents are

do not have an immediate need

kept in mind

when you choose

for

listed

some of

Some

of the features

below. Although most us-

these features, they should be

a text formatter or

word processor, and they

should be compared to the overall cost of the formatter in terms of required

memory, performance, ease of use, Page layout (margins,

tabs)

Document organization

Document

etc.

(outlining)

control (type, page numbering)

Paragraph control

(line spacing, indentation, styles)

Font control (type,

size,

spacing)

Table control (generation, placement, labels)

Graphics control (generation, placement, labels) Equation control (generation, placement, labels)

Cross referencing (sections, Lists

and indexes

cites, figures, tables)

(table of contents,

list

of figures and tables, index)

Bibliographic support

Document

sharing (incorporating and exporting text and graphics in differ-

ent formats)

Header and footer control User customization

This

is

not an exhaustive

list,

but should provide a basis for the capabilities

that are required in constructing a

document.

Many

of these features are not

needed by everyone, or by every application: however, they are fundamental to text production. In the following sections, text files with

be presented because ual pages.

We

we

will address the formatting of

two popular formatting languages. The it

is

a standard

will also present the L

UNIX A

nroff/troff

utility that is

package

will

used to prepare man-

T E X package (pronounced

LAH-TECH

i.

6.7 nroff

and

187

troff

it easier to use. in some respects, and is specifically directed at high document preparation [Lamport 1986]. For those who are interested. A A is similar to L T E X. and learning to use L T E X will simplify the process

because quality

HTML

HTML.

of learning

nroff /troff

For both

we

formatted without any commands, and then that

new

and latex, a

users can develop an understanding of

will slowly

how

text file will

be

add commands so

to use the utilities to their

best advantage. "&»

nroff and troff

6.7

nroff is

a text formatting language that formats text in files for typewriter-

like output devices

such as display terminals. The

nroff

matted using nroff.

and uses macro

ease,

is

designed

packages

to

UNIX

manual pages

produce documents with relative

to increase its versatility,

around for a long time. and. to some degree, has outlived Ch6

ertheless,

nroff is all UNIX

learned by

*a-

UNIX

a part of a standard users. After

nroff

is

nroff

found

tion can be

nroff-troff

6.7.1

in the

"nrof f- troff "

has been

Nev-

usefulness.

its

distribution

and should be

understood, other text formatting

and printing applications can more easily be appreciated. Examples

ip>"

are for-

in this sec-

directory.

Simple Application of nroff on a

File

One strength of nroff is that it can be applied to an unformatted file command line. Thus, nroff can be applied to "real-paper" as follows:

at the

localhost> nroff real-paper

nroff

produces a result similar to

cat

in that

it

scrolls off the page.

problem can be resolved by piping the nr o f f output through the

The nrof fed

window

size.

through

mail

file is

minimally justified

This can be useful

when

in

or posted to newsgroups.

sends this

new form to

This

utility.

80 columns, the standard terminal

writing documents which will be sent

When

the

nroff

does not change, since the text formatter merely reads the

nroff

more

the standard output, to a

is

file

file, to

issued, the file

and reformats

it.

another process,

or to a printer, depending on what the user wants to do.

6.7.2

Simple

In general,

ways than this,

1

.

A macro

is

nroff

is

used to modify the appearance of

just forcing

nroff

has

a series of formatting

with a specific name.

nroff Commands them

to a particular

command options which

commands

page

files in

size. In

more dramatic

order to accomplish

can be embedded into the text

associated with a particular function and invoked

file

by

1

OO

Chapter 6

File

Formatting and Printing

the user. For example,

Ch6

spaced, the

W&

spacing) alone

mands

nroff-troff/

into

you wanted

at the

beginning of a

real -paper and

the document.

real-paper

if

produce a

to

embedded nroff command

The

file

see

line.

how

to

do

file

this is '.

with the lines double

Is

2' (for double line

nroff com-

Lets put a few simple

they affect the display appearance of

below can be found

in the

"real -paper"

directory.

localhost> cat real -paper. nroff •ce

@

1

Graduating in Four Years: A Forgotten Trust .

ce

1

Bachelor •

.

ce sp

0.

Science

1

(2)

1

(3)

Abstract ti + 75in .11 -.75in A decade ago, the promise of a college education in four years was a real expectation for students in american universities. With the advent .

.

of

.

.

.

.ti -.75in

(4)

.11 +.75in

(f)

Introduction .

sp

2

@

.Is 2

This year will mark a decade in the information age. And with this age has come a terrifying realization that students cannot hope to assimilate the information required of them in an undergraduate program, and somehow put themselves through school, in a four-year term. .

.Is

1

sp

5

.

The Demise of Student Support for Higher Education The major threat to higher education in the past half decade has been the lack of educational support by the taxpaying public. The effective result is that students are, to an increasing extent, being forced to pay for their own education. Tie this into increased costs and time to graduation and the result is an ever decreasing number of graduating students The Increase in Required Information

.

command starts with a dot/period " " at the beginning of a new line, and that the command is not followed by any text. I have flagged six nroff commands that are worth noting in this sample. First, at item (1), the command " ce 1" tells nroff to center the next line, so as to look like Notice that every

.

a title.

rently

The next item is

(2) sets a

length has been reduced by the

mand 1

ent

temporary indent of whatever the indent cur-

work on both margins, the line same amount with the " 11 - 7 5 in" com-

plus .75 inches. In order for this to

.

.

(item 3). This will create an abstract for the paper. After the abstract, the

and

line length are returned to their starting values.

Item (4)

" .

sp

2"

6.7 nroff

simply

tells

nroff

to space

two

lines in the output,

line

spacing so that this paragraph

The

line

spacing

is

is

file is

and item

troff

(5)

189

changes the

double spaced, as previously mentioned.

returned to single spacing with

execution and output for this

and

" .

Is

1"

at

item

(6).

The

shown below.

localhost> nroff real-paper .nroff Graduating in Four Years: A Forgotten Trust Bachelor O. Science

Abstract A decade ago, the promise of a college education in four years was a real expectation for students in american universities. With the advent of ... Introduction This year will mark a decade in the this

age

information

age.

And

with

has come a terrifying realization that students cannot

hope to assimilate the information required of them in an

under-

graduate program, and somehow put themselves through school, four-year term.

in a

.

The Demise of Student Support for Higher Education The major threat to higher education in the past half decade has been the lack of educational support by the taxpaying public. The effective result is that students are, to an increasing extent, being forced to pay for their own education. Tie this into increased costs and time to graduation and the result is an ever decreasing number of graduating students. The Increase in Required Information

6.7.3

nroff, troff, and Macro Packages

nroff is used for displaying on typewriter-like devices, such as terminals. When you want to prepare a document that will be displayed in WYSIWYG format, or be printed on a high quality printer, then troff can be used. The differences between nroff and troff are related to the quality of the output device. On a workstation or laser printer, where the size, type, and resolution of characters can be controlled, troff will produce superior quality over nroff. For the most part, troff and nroff have compatible command sets, the output just looks different. For example, in nroff emphasized text

I

90

Chapter 6

Formatting and Printing

File

comes out on

as an underline, because

Using trof f emphasized

able.

a file,

you are using what

nrof f /trof f

is

an awkward

is

on a typewriter device

text

is

italics are

not avail-

When you execute nrof f nrof f The major drawback of

italicized.

called plain

command

.

set that is difficult to

remember. Sev-

macro packages have been developed that make it easier to format documents, where a macro is a mechanism whereby the commands needed to perform a particular function are clustered together and invoked with a single command. The user can use the macro packages or even develop their own macros. When nrof f is invoked with the '-m' option, a macro package is loaded that can be applied to the text file. Whatever appears directly after the 'm' must be a file located in the path " /usr/ local /tmac," and the file must be named "tmac CH." where "CH" stands for the file identifier. For example, the following command: eral

.

localhost> nroff -me real-paper .nrof

should execute

nroff

on the

file

real-paper

using the

"/usr/lib/

tmac /tmac e" macro package available to nroff. You can find out more how to get macro packages to work by reading the man page for nroff .

about

(man nroff). Four macro packages which are generally supported are the me (man 7 me), ms (man 7 ms). mm (man 7 mm), and man (man 7 man) packages. Examples in this section will describe how to load and use the me macros. Following the examples in this section, some plain nroff commands and some me commands will be tabulated for reference.

Loading a Macro Package or Input

6.7.4

own macro

In order to load your the one

below

at the

File

package, or input

top of your document source

file,

place a line similar to

file:

so ~/tmac/memacros

nroff command means switch the input source to the file folso command. In this example, the path and filename following "so" command point to a macro package where user-defined macros re-

The

Ch6

"

.

so"

lowing the the

.

j

wC^

side. In this

>rf-trofT/

ros" ros"

memacros

file

example, some macros from the user's personal

have been loaded.

directory. Inside the

(some commented) macros which can be used

The rate

so command can also be used nrof f / trof f commands. .

"tmac/memac-

A copy of this file can be found in the "memacmemacros file, there are several user-defined to

to input files

format complex documents.

which have

their

ow

n sepa-

6.7 nroff

191

troff

Creating a Simple Document File

6.7.5

Each

and

nroff document

age load

line, if

is

created with an editor such as vi.

such a package

is

used,

is at

The macro pack-

the top of the page,

and the

re-

mainder of the document and nroff (or macro) commands. As previously mentioned, an nroff command starts with a period in column of any particular line, and is immediately followed by the command name. The same is true of me macro commands. Most macros have different comconsists of text

l

mands

to begin

and end the context of the macro. For example, 1'

to

begin a

list

1' is macro used. Macros that are part of me are generally lowercase. Macros that are user defined are generally uppercase. Try running troff on the sample file "real -paper me" shown below.

item with me. the macro

*

.

(

is

used, and to end the

list,

the

'

.

)

.

localhost> cat real-paper .me .so UNIX/Ch6/nrof f-trof f /memacros/memacros .Is .

(T)

1

in +

.

5m

.11 5.7i .fi .

ce

1

Graduating in Four Years .

ce

A Forgotten Trust

1

Bachelor

0.

Sc ience

.sp 1 .

ce

1

Abstract •(q

(2)

A decade ago, the promise of a college education in four years was a real expectation for students in american universities. With the advent of •

.

.

.

.

)q

sh

(3) 1

"Introduction"

This year will mark a decade in the information age. And with this age has come a terrifying realization that students cannot hope to assimilate the information required of them in an undergraduate program, and somehow put themselves through school, in a four-year term... .sh

1

"The Demise of Student Support for Higher Education"

The major threat to higher education in the past half decade has been the lack of educational support by the taxpaying public. The effective result is that students are, to an increasing extent, being forced to pay for their own education. Tie this into increased costs and time to graduation and the result is an ever decreasing number of graduating students .

sh

1

"The Increase in Required Information"

(4)

1

92

Chapter 6

File

Formatting and Printing

This example

primary is

will

related to the text.

command. The what

is

is

paper. In this example, the

what

a set of locally defined macros and

com-

be effective for the entire document, but are not specifically

At item

abstract

called a quote

command

A

preamble

me

and references. Item

(1) begins

are those for headings

called the preamble.

mands which

typical of a simple

is fairly

commands

is

(1), a

macro

file is

being loaded using the

" .

so"

created by centering the abstract line and then using

paragraph environment, which

(item 2) and ended with a

heading. The heading level (here

1)

' .

)

q'

command

is

begun with

a

q' ' .

(item 3). Item (4)

indicates to the formatter

how

to

(

is

a

number

wrapped in double quotes. This heading is thus a first-level heading, or section. The output of running this example with nrof f is shown below:

the sections.

The

text of the

heading

is

localhost> nroff real-paper. me Graduating in Four Years: A Forgotten Trust

Bachelor

0.

Science

Abstract A decade ago, the promise of a college education in four years was a real expectation With for students in american universities. the advent of .

1.

.

Introduction

And This year will mark a decade in the information age. with this age has come a terrifying realization that students cannot hope to assimilate the information required of them in an undergraduate program, and somehow put themselves through school, in a four-year term... 2.

The Demise of Student Support for Higher Education

The major threat to higher education in the past half decade has been the lack of educational support by the taxpaying public. The effective result is that students increasing extent, being forced to pay for are, to an their own education. Tie this into increased costs and time to graduation and the result is an ever decreasing number of graduating students.

3.

The Increase in Required Information

6.7 nroff

nroff and troff Formatting

6.7.6

The

nroff

postprocessor

is

es

utilities,

at the

end of

nrc

Table 6.4:

In the

Although we

the interested user can find

and references

6.7.7

nroff

ff

Formatting

eqn

Generates equations

tbl

Generates tables

refer

Generates bibliographic references

nroff /troff Command

following sections, several plain the

man

pag-

utilities

Generates line graphics

Use commands.

in the

this chapter.

troduced.

prepro-

will not illustrate the use

more information

pic

Plain

A

itself.

whose output you can send to nroff before printing, and a a utility through which you pipe the output from nroff be-

fore sending the final output to a printer.

of these

193

text formatter has four utilities for generating specialized text

a utility

is

troff

Tools

types that can be used as pre or post processors with

cessor

and

Reference

nroff /troff commands

will be in-

examples as guidelines for understanding the usage of these

PAGE CONTROL One

of the

first

things a writer wants to do

the page:

Table 6.5:

" .

pi" and

* .

when

formatting a document

bp."

nroff Page control option reference

.pi ± Ni

Page length, where Ni

.bp

Start a

.pn r N

The next page

is

the

number of inches

new page will be

is to

me package, a couple of commands are used to define

set the pagination. In the

numbered N

(default

is

1 1

I

94

Chapter 6

File

Formatting and Printing

LINE Table 6.6:

CONTROL

nrof f Line control option reference

.11 Ni

Ni

number of inches

Line length, where

na

t=>

No

adjust on justification; leaves ragged right page

.nf

No

fill;

.fi

Fill;

ce N

Center the next

ul N

Underline the next

Continuous underline

sp N

Space

.Is N

line spacing (e.g., single spaced:

Turn on output

.

.

•

.cu .

.

nm N M S

I

same

same

N

is

the

as verbatim (left justify; for

as full justification left

N

vertically

N

6.5)

code display)

right

lines

lines

N

=

1)

numbering

line

Line number

starts with, or

at

incremented

to,

N (e.g., N=3

starts line

3)

Line numbers for lines of multiples of M

M

is

lines

N

numbering

and

(default

(e.g.,

M=2 numbers

every other line)

S

Line numbers and lines are separated by S spaces

I

Line numbers are indented by I spaces

MARGINS AND TABS Table

6.7:

nrof f Margin and tab control option reference

•in ± Ni

Indentation,

•ti ± Ni

Temporary

Tab;

•

ta Nt

N

when Ni

specifies the

indentation.

number of inches

+ before paragraph and

identifies location

after

paragraph

and t the type as declared by the characters below:

Right justified tab

Center adjusted tab Left adjusted tab

-

offset.

6.7 nroff

and

troff

195

FONT TYPE AND SIZE Table 6.8: .

ps ± N

.

ft

nroff Font type/size control option reference

F

fp N F

ps ± N

Set point size, can also use

Font changed to F. where F

R

-

Times roman

I

-

Times

B

-

Times bold

-

Symbol

is

inline

the font

name

(default

roman)

italic

Font position, where font

is

loaded (1-4) where the correspondence

between character font type and font position

Fl

-

roman

F2

-

italic

F3

-

bold

F4

-

courier

is

tabulated below

commands can be issued inline with the use of the command. For example, the following command changes the font types using both Point size and font

the character

\fB See

f?

and font position methods:

Spot \fl run \fR

will

produce

See Spot run

The same \f3 See

s

*fl

effect can be

Spot \f2 run \fl

produced with the font position

1

9b

Chapter 6

File

Formatting and Printing

HYPHENATION To prevent a word from being hyphenated,

%

type

at the

beginning of the word

with no space.

Table 6.9:

nrof f Hyphenation control option reference

.nh

«•

.hy N

No

hyphenation

Automatic hypenation on; the number

N indicates how many

characters to keep

together before splitting

MISCELLANEOUS nrof f Miscelaneous options reference

Table 6.10: .tl

'

left center right '

'

Three-part

title;

text

between quotes

fied, center justified,

and

.

ds xx string

Define a macro

End

Define a string

a

macro

be

left justi-

right justified with the cur-

rent margins of a line

.de XX

will

xx

definition

xx containing

string

6.7 nroff

Command

6.7.8

Reference for the

and

troff

197

me Macro Package

SECTIONING Table

6.1

1

:

me Heading control option reference

Sh LEVEL "LABEL"

Create a section heading, with its

LABEL

as

its title,

and

LEVEL

as

depth; level values are associated with the following section

types (0

< LEVEL
cat sample -man. nroff .TH FOOBAR 1L "vax version 1" "CSC212 Demo Man" SH NAME

FOOBAR

99

Documentation using nroff 1

A sample program documentation file

.SH SYNOPSIS

foobar file

(I)

[

listl

]

...

[

listn

]

.SH DESCRIPTION

Foobar doesn't do anything. This is simply a syntax example. .SH AUTHOR

Jake Foobar .SH EXAMPLES

Try:

EX %

(4)

foobar sampman

.HE .SH SEE ALSO .SH FILES .SH KNOWN BUGS

There are no known bugs, yet, but there isn't any code either.

The headings are taken from the standard cluster of man page headings that was mentioned in Chapter 3 and page 65. The .TH (item 1) creates the title bar of the online document. The first and second items are the program name and section, respectively. They should not be quoted. The third item is a reference to the architecture the program is running on. The fourth item is a comment written in the footer. The third and The noted items

are described below.

fourth items must be quoted. Notice that this three-part

is

an adaptation from the

nroff

title.

Item (2) uses the .SH text associated with the

command to produce

heading for item

(2).

a subject header. Item (3)

Without other commands

is

just

text is

200

Chapter 6

File

Formatting and Printing

justified as ting an

normally the case in

nr o f f

.

Item (4) identifies a macro for format-

example. The .EX begins the example, and the .EE ends the example.

The macro formats an example by

commands

Additional

setting a

temporary indent for the paragraph.

more elaborate documents

for designing

are tabu-

lated below.

Viewing the Online Documentation

6.8.2

You can view

the

arguments. The

document you

create

File

by calling nroff with the appropriate

commands provided below

are the ones used

when man pages

are displayed:

nroff -man

tbl file

The tbl

more

col

-

was mentioned

utility

in a

previous section.

postprocessor which formats tables. The

col

playing multiple column

text. If

as that above, then these

commands can be

use

is

the

-man macro

more. The hyphen

call

you want

to

utility

It is

an

nroff

works with tbl

pre/

for dis-

produce a simple document, such left out.

The

part

which you must

and the subsequent (recommended) pipe through

in the sixth position in this

command

is

often used with

which expect a filename as an argument, and represents the standard input even though the utility is getting its input piped in. Below is an example of this command applied to the sample document file "sample-man. utilities

nroff." more localhost> nroff -man sample-man. nroff FOOBAR(IL) UNIX Programmer's Manual |

NAME FOOBAR

-

A sample program documentation file

SYNOPSIS foobar file

[

listl

]

.

.

.

[

listn

]

DESCRIPTION Foobar doesn't do anything. A complete fake.

AUTHOR Jerk Fc bar continued

FOOBAR(IL)

6.8 Online

Documentation using nroff

201

EXAMPLES Try: %

foobar sampman

SEE ALSO FILES KNOWN BUGS There are no known bugs, yet, but there isn't any code either.

The output for man formats is the standard 80 columns by 66 lines. Page numbers appear at the bottom of each output page with odd page numbers appearing on the right side and even page numbers appearing on the left side. I have collapsed some of the lines from this output to save space, but you should get the idea.

Making

6.8.3

When you

the Online

finish writing the

Document Available

program and the online document

is

also correct,

then you need to place the document into the directory where the application will reside

and make sure

that the

These considerations

also.

guage

is

will

command

to read the

be continued

when

the

document is available C programming lan-

introduced, because program writing and documentation are very

closely related.

6.8.4

Some

nroff Man Macro Package Command of the

commands

below pertain only

to

for creating online documentation are included in the

(man nroff.

following table. Refer to

Reference

7

man)

for additional

commands. The

entries

202

Chapter 6

Table 6.14: .B

File

Formatting and Printing

nrof f Man macro options reference

[TEXT. ..]

set in

•CT CHAR

TEXT

Sets text

in boldface; if

no

text

is

specified, the next text line

Prints the

;

keyboard control character indicator

CW

Sets text in constant width font until another font change

.EE

Ends an example and

.EX

[i]

width font with 'no allowed)

HB [words

fill'

mode

.

EX and EE

printed in a constant

is

.

(no text wrapping and blank lines

in effect

mode

Sets the text in underline

.11 word

Sets a temporary indent to the length of the specified

word

Reverses one line and then

.

.12

.

.

.

specified

•

PN x[y]

Sets

x

PP

.R

sets a

temporary indent to the length of the

constant width typeface and then reverts to the previous

y

Starts a block paragraph; sets the prevailing indent to

Sets the text in a

roman typeface

until

tered. Also ends nrof f underline

.RN .RS

[i]

Prints the return character indicator,

Shifts the left .

RS

margin

5i is

encoun-

amount of i

indents.

was or

in effect

to the right (relatively) the

macro can be nested up to nine levels deep

TEXT

Creates a section header with

.SS TEXT

Creates a subsection header with

TEXT

Begins a new reference page and

sets the

TH ncafx

if it

.SH TEXT

.

.

another font change

mode

The

word

word

in a

typeface,

•

found

is

and indents

restores basic text defaults

example. Text between

Starts an

for

A prints

example. .CT •

name; c

to the section;

"VAX",

f to a footer

page

title:

n refers

to the file

a to an optional machine architecture, such as

component; and x

to an extra optional

commen-

tary such as "unsupported"

,TP

[i]

Sets the prevailing indent to i, then begins the indented paragraph

with a hanging tag given by the next text the

is

boldface

macro places

line: if the lag

the next text on a separate line

docs not

fit.

6.9

LATEX

203

6.9 L A T E X L A T E X and T E X are text formatting languages similar to

tex and tex

are the associated compilers

nrof f/trof f la.

which are widely used

for produc-

ing articles, books, and letters which can be sent directly to a phototypesetter

such as a Linotype®. Their popularity partly

on a more mnemonic

set

is

based partly on their semantic

clarity,

of commands, partly on the development of bit-

map previewers, and partly on the fact that the source file remains in ASCII. latex and tex can be used on a wide variety of hardware platforms: Sun, HP. DEC. NeXT. Apple, and IBM, to name a few. The commands are fairly easy is gradual for complex documents. In compared to the competition, latex (tex) is quite reasonable. Presented here are a few examples for using latex. There are six

to follow, although the learning curve

general, and especially

Ch6

important things to consider source

file,

command

(3)

supplementary

(6)

when

latex:

using

(1) the

environment, (2) the

running latex, (5) printing the file, and Sample examples will be provided, annotated, and

files, (4)

utilities.

The files used in these examples can be found in the "latex" diMore examples appear in Appendix L along with some comparisons

explained.

latex

rectory. to

HTML.

L TgX Source

6.9.1

As

File

,

have a terminal equivalent, so Ch6

Paper

nrof f and trof f the basis for latex is a source file containing text latex commands. Unlike nrof f, however, tex and latex do not

in

and

for a Simple

Script

and then placed into

signed to send

nrof f The .

its

all

this

examples must

output to a terminal,

simplest form of

first

be converted to Post-

document. Also, because it

latex

latex

cannot be run on raw text source must

still

is

not de-

files as

have a few

can

latex

commands embedded in it. Consider a simple modification to real -paper, called "real -paper tex," and located in the "real -paper" directory, which can be compiled with latex. All that you do is wrap the text inside the

latex/

real-paper

.

following

lines:

\documentstyle{article} -* \begin{ document}

(l) (2)

% %

.

©

BODY OF REAL -PAPER

% \

end {document}

—

-«

The latex document called the

1.

Unless a

command

file is

preamble.

used.

is

comprised of three sections. The

In the preamble, the type of

document

is

first

(4)

section

is

established. For

204

Chapter 6

File

Formatting and Printing

example, the is

first line

of the

a required line in the

file,

file, at

to

an "article"

mands,

title

style,

which

is

(1),

defines the documentstyle. This

because the document must be formatted

particular style. In this example,

can be found

item

real -paper

is

to

some

being formatted according

the format for a journal article. Other items

which

preamble are user-defined macros, page numbering cominformation, and so on. in a

The second

document

part of the

is

the

document body

itself

(item 3), and

must be identified by a beginning (item 2) and an end (item 4). The text of the document, and its formatting, are written where item (3) is. The percent-sign (%) is the tex and latex comment character. All three segments are required

latex

Given these minimum requirements, real -paper can be formatted. Granted it will not look too pretty, because nothing else has been added, but will be equivalent to running nrof f on the statements in a

plain version of

source

file.

real -paper.

The last section of a latex document is the closing segment, or postamwhich is located between the document ending item (3) and the end statement (4). In the example above there isn't anything of note in the closing segment, but this is where the bibliography style would be identified. ble,

Executing

6.9.2

Once

latex on

the Simple Paper Source File

the source file has been created,

ply the function

la tex to

it is

a simple matter to use

latex. Ap-

the source file as follows:

latex source filename Below

is

the trace of

latex'ing "real -paper

.

tex":

localhost> latex real-paperO.tex This is TeX, C Version 3.0 (T) (real-paperO tex (2) LaTeX Version 2.09 (/usr/f 1/ jhodges/TeX3 /usr/ local /lib/ tex/ inputs /art icle sty (5) Document Style 'article' . (real -paper .aux) /usr /local /lib/ tex/ inputs /art 10 .sty) (/usr/f 1/ jhodges/TeX3 (T) (real-paperO .aux) [1] (s) Output written on real-paperO dvi (1 page, 1628 bytes). Transcript written on real-paper0.log. sfsuvaxl [272 dvi2ps real-paperO > rpO.ps [/usr/f 1/ jhodges/TeX3 /usr /local /lib/ tex/ tex. ps] [1] .

.

.

)

.

)

.

©

]

.

6.9

LATEX

205

The execution trace shown above should be explained. First, item (1) shows the tex version number, which may be significant if you ever have problems with it. Second, item (2) shows what file latex is compiling. Item (3) shows where latex has found the requested documentstyle. In this case, all files relating to

tex reside in the

tory off the directory nifies that

page

1

where tex

"/usr/ local /lib/ tex/ inputs" is

installed.

At item

has successfully been compiled.

the compilation has gotten because the page

(4),

You

note the

can always

numbers are listed numbers in

the compilation proceeds, tex also displays line

something interesting

is

detected.

and context will be displayed. In

When

this

an error

is

"real-paperO .dvi."

This

file

direc-

This sig-

tell

in this

how

far

way. As

the text file

detected, the line

if

number

example, there was only one page of text,

so the compilation was successful. The final output written to

[1].

is

noted

at

item (5) and

dvi stands for device independent

is

file.

can be translated to forms suitable for display and printing, such as

PostScript.

Item (6) case, file,

I

a

decided to

which

Note

is

that

I

I

new command, one of many possible "next run a conversion from real -paper dvi .

file, is

1.

2.

it

have directed the output

the compilation phase,

lists

shown

to a PostScript

have included below. This was done with the function dvi2ps.

the page

numbers

as

"rpO ps." This file can be book with the special command."

to the file

printed with Ipr or, in this case, input into this

As with

steps." In this

.

when dvi2ps begins working on the "dvi" completes its translation. The final product

it

in Fig. 6.2.

Some versions use a function called dvips. One way to incorporate a postscript figure into

a

latex document

is

shown

in

Appendix B.

206

Chapter 6

Figure 6.2:

File

Formatting and Printing

Result of minimal changes to Graduating

in

real-paper

Four Years:

A

for latex compilation

Forgotten Trust

Bachelor O. Science Abstract

A decade ago. the promise of a college education in four years was a real expectation for students in american universities. With the advent of ... Introduction

This year will mark a decade in the information age. And with this age has come a terrifying realization that students cannot hope to assimilate the information required of them in an undergraduate program, and themselves through school, in a four-year term...

The Demise

somehow put

The major threat decade has been the lack of educational

of Student Support for Higher Education

to higher education in the past half

support by the taxpaying public. The effective result is that students are. to an increasing extent, being forced to pay for their own education. Tie this into increased costs

number The

6.9.3 If the

and time

to graduation

and the

an ever decreasing

Debugging a latex Compilation

latex compilation

runs into problems, then they will be flagged as the

If the

compilation runs into a problem

then n stops and waits for your instructions. will sec a question in

is

Increase in Required Information

compilation continues.

you

result

of graduating students.

mark

(?). If

you type an

debugging the compilation. Some of

others aren't.

You can always

When

'h' after this, its

it

cannot resolve,

the compilation stops,

comments

tex will

you

try to assist

are pretty useful

and

type a carriage return and try to resume the com-

LATEX

6.9

You can

pilation.

also type an 'x' to quit, or an 'e' to edit, at

default editor will be invoked and place at the line

When you

Wrapping detracts

will be able to recompile the file.

File

a couple of commands around the text in a

file is fairly

document.

intent of the writer; to prepare the to the file, then

discern the administrative

and

last

commands

rate file, called a

commands,

command

it

the

command

file

and commands somewhat separate, and

j^y^ latex/

comfiies

A

in the

As a result, sometimes it is easier preamble in particular, into a sepa-

itself.

the

commands

are always exe-

way of formatting

cuted the same way. and they do not get in the

Although unnecessary, a

difficult to

preamble and postamble)

Then, the general

file.

harmless, but

When you add

becomes more and more

(i.e..

segments from the paper

to consider placing these

Ch6

which point your

where the error occurred.

from the

many such commands first

you

The Command

6.9.4

it

exit the editor,

207

the

document.

enables the user to keep a document to define useful

macros for massaging

command file, "rp0com.tex," one that can be used to format "real -paper tex." is shown below. This file can be found in "comf iles" directory. In addition, two sample command files ("com. tex" and "sfsu.tex") are provided and explained in document appropriately.

the

simple

.

Appendix

L.

localhost> cat rp0com.tex \ document style {article} \begin{ document} \include{real-paperO} \ end {document} \end

Note

it

lines labeled item (1)

the "\

like the template

and item

(3). the

include" command

provided above. The

paper

(item 2).

real -paper is

will require that the file

file named "real -paper tex." prompt the user for another name, latex name end in " tex." but you do not have to type the it

6.9.5

The

file

Preparing the L

.

will

.

real -paper latex commands only.

suffix.

being read into

The include com-

searches the current directory for a

does not find one. then

line"

much

instead of placing the text associated with

document with

mand If

(3)

is that,

between the

this

(2)

that this file looks very

difference in

(T)

.

tex

can

now be comprised

TrX Document

of text and

'"in-

File

you have seen how to execute latex on a minimally altered file. The reason for that was to prove to you that you can do it. Preparing a document

So

far,

with a formatting language can be as frustrating as writing a computer pro-

gram, maybe more

so.

You want the

result to

look a certain way, and you sense

2Uo

Chapter 6

File

that it

Formatting and Printing

it

can be done, but you keep getting compile

works or

to locate

it

doesn't, but in a

document

errors. In a

program,

at least

errors aren't always obvious, nor easy

and eradicate. As an introduction

to text formatting with

real -paper

latex, we

tex. This time, the required formatting commands will be embedded, and we will look at each one and explain what it does. We will then execute latex on the file, and print out the result as before. After that, you can simply take a copy of the source file and replace it with your own text, and it should prepare a nice looking class paper for you. There are two types of commands that you should be familiar with in latex: (1) preamble commands, which you have seen a few of already; and will take a look at preparing

(2) text (inline)

mands title is

.

commands, latex commands

in that they look like

called "title," and the

are different

words. For example, the

from

command

nrof f comfor

making a

command to make a section-level heading is called

"section."

Preamble Commands

latex is designed to produce a document whose page layout is precommands that either initialize latex and select the paper layout, or tell latex how to override or add to the paper Although

defined, the preamble consists of all the

format as a whole. These are page layout commands. For example, consider the first line of the file

\

rpOcom. tex

above.

document style {article}

The essence of a latex document

is

the documentstyle.

The document-

"article sty," which is a template or style file for the document. The style file tells latex how to format the document. For example, article sty tells latex that the docustyle file, in this case

"article"

stands for

.

.

ment

will use a technical article format.

page

size,

that

style file for articles then sets the

margins, font type and sizes, headings, text spacing,

might go into a journal. The

pers, since

The

it

is

macros defined

article style file

already a formal presentation. in

tex and

latex. The

idea

A

is

style file is

to

etc. for a

paper

can also be used for term padesigned using the

hide from the user the task of

building a page and a paragraph and leave the author the task of preparing the

content of the paper.

If

you change the

style file of the

document, but keep ev-

erything else the same, then the document will look very different. This

of the strengths of latex.

A

latex document

style

can be modified by adding other styles on top of it. That

is

is,

documentstyle

are hierarchically organized and support property inheritance.

syntax for documentstyle use in a

\

document style

[

latex

optionl, option2,.„.

]

file

follows:

{style}

is

one

only a template, and files

The general

6.9

where "style" can be any of the following

LATEX

209

(partial list):

book.sty article. sty

report. sty

msthesis.sty diss. sty letter.sty

Notice that the the suffix

is

files

have the suffix

" .

For example, the default type size for the

"article"

user can elect to have the document printed in tional

\

latex

sty." As with other

files,

not required but assumed. Options can be used to modify a style.

1

style

lpt or 12pt

lOpt. But

is

the

by providing an op-

argument:

documents tyle [12pt] {article}

A

few of the options available are tabulated below: • •

lOpt lpt

1

•

apalike

•

tvvocolumn

When Ch6

the author decides to

modify the

style of their

need change the documentstyle and future versions of the This capability makes

latex

an extremely powerful

document, they only file will

tool.

be changed.

Of course,

a docu-

mentstyle can be edited to suit one's particular needs, but then you must understand tex

much

better. All the standard

"/usr/ local /lib/tex/ inputs" ested, there are

documentstyle

files are

located in the

directory. In addition, if

some home-brewed document

styles in the

you

are inter-

"texmacros"

di-

rectory.

Text

Commands

There are two types of text commands

embedded

commands

or inline

in latex: commands, latex commands

in that they

backslash (\)

at the

off with curly braces

low.

look like words.

beginning of a (

{ } )

new

within the

( 1 )

line

commands

are different than

and

(2)

nrof f

A latex line command starts with a line. A latex inline command is set

text.

An example

of each

is

provided be-

210

Chapter 6

File

Formatting and Printing

\ small this text would appear smaller than normal

\normalsize this text would appear normal again

However,

the

same thing could be done,

inline, as follows:

small this text would appear smaller than normal} \\ \normalsize} this text would appear normal again}

{\ {

Line

commands

changes, while inline other references.

6.9.6

are used to

commands

change paragraph are

most often used

The double backslash (\\)

The Source

File for a

styles

and more global

for emphasis, cites,

and

forces a carriage return.

Simple Paper

Now we will look again at real -paper tex, a version which has latex commands for formatting it in article style. I have not used a command file so .

that the reader

can appreciate the difference.

localhost> cat real-paper.tex \ document style {article} \begin { document

\title{Graduating in Four Years: A Forgotten Trust} \author {Bachelor 0. Science} \date{} \maketitle \vspace{0 5in} .

\begin{abstract A decade ago, the promise of a college education in four years was a real expectation for students in american universities. With the advent of

.

.

00 (2)

® (i) (5)

(6)

.

\end{abstract \section{ Introduction}

(j)

This year will mark a decade in the information age. And with this age has come a terrifying realization that students cannot hope to assimilate the information required of them in an undergraduate program, and somehow put themselves through school, in a four-year term... continued

6.9

LATEX

21

\section{The Demise of Student Support for Higher Education} The major threat to higher education in the past half decade has been the lack of educational support by the taxpaying public. The effective result is that students are, to an increasing extent, being forced to pay for their own education. Tie this into increased costs and time to graduation and the result is an ever decreasing number of graduating students

\section{The Increase in Required Information} \ end {document} Vend

This example I

will

The

show

is fairly

a sample

typical of

command

file

latex papers

not using a

for the paper after

line labeled (item 1) indicates the

paper

title.

I

command

file.

discuss this version.

Titles cannot be

broken into

you cannot use two backslashes, as mentioned above, to The paper's author is formatted with the \ author command at item (2). With this command, you can use backslashes to break up the author field in \ author. This will allow you to put your address, school, or course in the same format and location. Item (3) illustrates the use of \date to label the date of the publication. This can be made blank as shown. The \maketilines arbitrarily, so start a

new

line.

tle command

(4) generates the

title.

Note

that maketitle

must be

after the be-

ginning of the document. The line in which item (5) occurs illustrates the creation of vertical space using the

\vspace command.

Vertical and horizontal

space require an argument. The argument must have units, and the units can be

An abstract \begin{abstract}

inches, centimeters, millimeters, picas, and points.

with

paragraph

the

stract},

command

.

can be created .

.

\end{ab-

and end and an indented paragraph in

as noted at item (6). All paragraph styles start with begin

with end. The abstract paragraph creates a smaller type.

The

There are

heading depths

six

line in

which item

subsection are numbered. In

title

(7) occurs creates a first-level heading.

latex, but only part, chapter, section, and latex, all numbered sequences are generated in

during the compilation, so the author need not worry about section numbering.

moved, latex reorders the numbering the next time the document is compiled. The final note (item 8) illustrates how the document is ended, which ends the document paragraph style, and the paper. If sections are

As an

aside, the file

real -paper tex need not have a preamble if the command file. A command file for this paper .

author had decided to use a

would have been simple

to produce, as

I

have done

in the

next example.

212

Chapter 6

File

Formatting and Printing

document style {article} \begin document \title{Graduating in Four Years: A Forgotten Trust} \author {Bachelor O. Science} \date{} \maketitle \vspace{0 5in} \begin{ abstract} A decade ago, the promise of a college education in four years was a real expectation for students in american universities. With the advent \

{

.

of

.

.

.

end {abstract} \ inc lude { real -paper \ end document \

{

6.9.7

Running L TrX on the Simple Paper

The

was compiled with latex

file

as

shown below and

printed as illustrated

in Fig. 6.3

localhost> latex real-paper This is TeX, C Version 3.0 (real-paper tex LaTeX Version 2.09 /usr/f 1/ jhodges/TeX3 O/usr/local/lib/tex/inputs/article sty Document Style 'article' . (real-paper aux) /usr/ local /lib/ tex/ input s / art 10 sty) /usr/f 1/ jhodges/TeX3 (real-paper aux) [1] Output written on real-paper .dvi (1 page, 1720 bytes). Transcript written on real-paper.log. localhost> dvi2ps real-paper > rp.ps [/usr/f 1/ jhodges/TeX3 O/usr/local/lib/tex/tex.ps] [1] localhost> .

.

(

.

(

.

)

.

.

.

)

.

6.9

Figure 6.3:

213

LATEX

PostScript output from latex applied to real -paper tex .

Graduating

in

Four Years: Bachelor

().

A

Forgotten Trust

Science

Abstract

A real

1

decade ago. the promise of a college education in four years was a expectation for students in ameiican universities. With the advent of

Introduction

This year

will

mark a decade

in

the information age.

a terrifying realization that students required of

them

through school,

2

in

:

umot hope

And

with this age has come

to ascimilate the information

an undergraduate program, and somehow put themselves

in a four-year term...

The Demise

of Student Support for Higher

Education The major

threat to higher education in the past half decade has been the

lack of educational support by the faxpaying public.

The

effective result

that students are. to an increasing extent, being forced to pay for their

is

own

education. Tie this into increased costs and time to graduation and the result is

an ever decreasing number of graduating students.

3

The Increase

in

Required Information

Preparing Complex Documents

6.9.8

To use latex on a complex document, document has at the

several passes

must be executed.

If the

a bibliography, then the bibliography can be included directly,

end of the document, or be included separately,

in

which case

it

will be

placed on a separate page. The format for creating bibliographic entries, index entries, start

run

and cross references are discussed

in

Appendix

L. All included files

on a separate page. Either way, you must run bibtex on the

latex

on the

file.

have prepared the index

Likewise,

if

entries, then

you have an index

in the

file after

you

document, and

you must run makeindex on the

file after

214

Chapter 6

File

Formatting and Printing

latex on the file. The order between bibtex and makeindex is unimportant. Next, if you have any cross references in the file, then you have to run latex on the file again just to generate and resolve the references. you have run

They

are gathered together after the first pass and then placed on the second

one. Finally,

if

you

are planning to put a table of contents,

latex again,

of tables into the document, you have to run tions lag the processing

of figures, or

list

list

because these func-

by one cycle. Of course, a single pass can accomplish

latex compilations are required in adsuch as bibtex or makeindex. At each

any of these tasks, but generally two dition to stage,

any postprocessor runs,

latex produces a file called "file .dvi" which can be sent to an

put device. So you need not run

all

these passes

when you

are

out-

trying to

still

you have done all these passes will the document print correctly. It should be noted that if you do not modify the index entries or the bibliographic entries, then you do not have to keep running makeindex and bibtex. The overall template is shown below: compile the document. Nevertheless, only

Run latex on

•

("file.tex" •

the

the

("file.aux," "file.idx"

=>

the

Run latex on

the

document

=>

file

"file.ind")

document

("file.aux," "file. bib" •

file

"file. toe," "file.lof," "file. lot," "file. dvi")

Run makeindex on Run bibtex on

•

document

=> "file.aux,"

after

file

"file.bbl")

document

to import ".ind"

("file.aux," "file.ind," "file.bbl"

=> "file.aux,"

and ".bbl"

files

"file. toe," "file.lof." "file. lot."

"file. dvi")

Run latex on

•

the

document

to resolve references

("file.aux," "file.ind," "file.bbl"

=> "file.aux,"

"file. toe," "file.lof." "file. lot."

"file. dvi")

Run dvi 2ps on

•

("file. dvi"

=>

the

document

"file.ps")

latex is the executable which compiles the document file in a manner nrof f latex produces a number of files which are editable but not, in general, of much use to the latex neophyte. One of these files is called "file aux," which is required by the bibliographic reference utility bibtex. An embedded preamble command, makeidx. produces a file called "file idx." This file can be used with the program makeindex to produce similar to

.

.

.

an index. The resulting passes are required

is

called

file is

"file, ind." The reason

man)

and

to re-

to build the "file.bbl" file (the reference file),

solve cross references within the document.

can execute the

that so

utility

dvi2ps

takes the device independent

file

this

process

on the "file. dvi" created by

Script suitable for printing with Ipr or

ports a PostScript previewer.

When

latex

file

is

done, the user

dvi2ps

created.

and translates

it

to Post-

previewed on a workstation which sup-

LATEX

215

dvi2ps

does not

6.9

dvi2ps file

>

file.ps

which

will write the output to the file

need you

to type the ".dvi" suffix

bibtex

postamble, and

"file

on the

.ps." Note that

file,

latex

does not need the ".tex"

does not need the ".aux" postamble. All of these are

the default expectations for their respective utilities.

properly formatted,

it

When

the

document

is

can easily be printed on a laser printer with the following

command:

dvi2ps file

lpr -Ppr inter-name or you can use the

"file .ps"

created from a

dvi2ps

run directly, as

fol-

lows:

lpr -Pprinter-name file.ps

6.9.9

L A T £ X Command Reference

N

measurement and the associated value. If unspecified, the unit is assumed to be pixels in 72 dots per inch (dpi). Inches can also be specified as "in." Every command is asIn each item in the following tables, an

sumed

to follow the

(\) in

column

slash.

An

1

of a

format above. That line,

or

it is

refers to a unit of

is,

enclosed

each item

"item" assumes curly braces around

are used, they

must be used only

entire paragraph style.

propriately.

at the

starts

with a backslash

in curly braces ({ }) it.

and the back-

When "begin" and "end"

beginning of lines since they reflect an

Paragraph styles can be nested but must be balanced ap-

216

Chapter 6

File

Formatting and Printing

DOCUMENT CONTROL Table 6.15:

latex Document control options reference

\documentstyle [options] {style}

Basic document page layout, font selection, etc.

\pageheight {N-units}

Length of page

\pagewidth{N-units}

Width of page

\leftmargin{N-units}

Size of

\rightmargin{N-unit s

Size of right margin

\title{TITLE}

Document

\ author

{TEXT}

Names, addresses,

\ thanks

{TEXT}

Acknowledgments

\begin{ abstract}

.

.

.

\ end

{abstract}

margin

left

title

No

\listof figures

No argument

\listof tables

No argument

\date{item}

Current date

.

.

.

\ end {

of authors

Abstract environment

\tableof contents

\begin{ document}

etc.

document

argument

Document environment

\maketitle

\ inc lude { DOC

Put the Insert

title

DOC

here, after to

\begin{ document}

compile here;

DOC name

ends

with ".tex" \ appendix { TEXT

Chapter level header with

\print index

Print the index

\bibliography{FILE}

Name

of

file

of bibliographic entries:

FILE

".bib"

Type of bibliography formatting

STYLE

text

now

name ends with

\bibliographystyle { STYLE

TEXT

type ends with ".sty"

desired;

6.9

LATEX

217

PAGE CONTROL Table 6.16:

\newpage

latex Page control options reference Break page here and

start a

new page

FONT TYPE Table 6.17:

Lat ex Font type options reference

{\bf item}

bold font

{\em item}

emphasis,

{\sf item}

san

{\sl item}

slant type

{\tt item}

typewriter (constant width)

italic

serif

font

FONT SIZE Table 6.18:

latex Font

size options reference

\tiny

tiny text

\ footnotes ize

footnote-sized text

\normalsize

normal-sized text (for style option)

Marge

large text

\Large

Large text

\huge

huge

\Huge

Huge

text

text

218

Chapter 6

File

Formatting and Printing

HEADINGS The following for the

list illustrates

the font type and size, and

"book, sty" documentstlye.

cle. sty, will differ in

Table 6.19:

how

numbering schemes,

Different documentstyles, such as

headings are formatted.

latex Section header options reference

\part{Part}

Parti

\chapter{ Chapter}

3 Chapter

\ sect ion

1.1 Section

\ subsection {Subsection}

t=>

1.1.1

\subsubsection{Subsubsection}

Subsubsection

{Sect ion}

Subsection

\

par agr aph { Paragraph

Paragraph

\

subparagraph { Subparagraph

Subparagraph

arti-

6.9

LATEX

219

PARAGRAPH STYLES Table 6.20:

latex Paragraph

\begin{ enumerate}

.

•

style options reference

.items.

.

.

\ end

{enumerate}

1

.

Numbered

list

of

items

\begin{ itemize}

.

items

.

\begin{description}

.

.

.

.

.

\end{ itemize}

.items.

.

.

• Bulleted list

\end{description}

Item

of items

text in the

paragraph

is

indented under item

\begin{abstract}

.

.

.text

.

.

.

\end{abstract}

abstract Indented

and

justified

text

with "abstract" centered above

\begin{quote}

.

.

.text

.

.

.

\end{quote}

Indented and

justified text

\begin{verse}

.

.

.text.

.

.

\end{verse}

Indented and not

justified text

\begin {verbatim}

.

.

.text.

.

.

\ end

{verbatim}

Format exactly as typed in constant width font

For each item

in a

paragraph

style, the

item

is

designated as shown below

for the itemize paragraph style:

\begin{ itemize} \item{Iteml text} \item{Item2 text}

\item{Itemn text} \end{itemize}

•

Bulleted List of Items

•

Iteml text Item2 text

•

...

•

Itemn text

The itemize and enumerate paragraph styles have optional arguments which enable the writer to modify how items will appear. The optional arguments are used in the same manner as for the required argument to the description format.

22U

Chapter 6

File

Formatting and Printing

begin {description} \item[Iteml] {Text for iteml. We show how the description format plays with these items.} \item[Item2] {Text for iteml. one we will make extend to a new also } \ end { deer ipt ion} \

Iteml Text for iteml. We will show how the description format displays with these items.

will dis-

— This line

Item2 Text for item2. This one we will make extend to a new line also.

.

where the description

in

square brackets, for the description format,

For the itemize and enumerate paragraph

numbering mechanism, are placed

in the

is

bold.

styles, the optional bullet type, or

square brackets. See [Lamport 1986]

for details.

FIGURES and TABLES Table 6.21

:

latex Figure

control options reference

\begin{ figure} [htbc]

.

.stuff. \end{f igure}

\begin{ table} [htbc]

.

stuff.

.

.

.

Figure environment

\end{ table}

Table environment

h

Place the figure or table here

t

whoami jhodges

Alternatively, the

guments), which will

who command

tell

!

7.3.2

who am

i (with

two

ar-

the current user/host combination, the login port, the

date and time of login, and port

localhost> who am i sfsuvaxl jhodges ttyqc Jul 18 13:35

has an option,

(e.g., tty)

of login.

(modeml3.sfsu.edu)

Anyone's Status

The finger utility was introduced in Chapter 3. finger is useful on a network to find out who is on the system, and can be used when trying to find out who is logged on to a host whether you know a user's account name or not.

finger

can also be used as a general rolodex for users, because

it

displays

i

230

Chapter 7 Network Processing

make available shown below:

general information about a user that the user has decided to the general public.

The standard syntax

for

finger

is

to

finger [name] @host where "name"

is

optional, and can be any single string of characters, repre-

senting a person's userid, their

from the command, finger

ted

host

can be a local host, a

a local host

host

is

name

and a

list

will

name,

list all

their last

name,

etc. If

name

is

omit-

users logged onto "host." Likewise,

symbolic name, or an IP address. On finger command without a host and the local you can issue the finger command without a

full internet

you can issue the

assumed. Likewise,

first

of all users on that system will be displayed. For example,

say you want to see

if

anyone

is

logged on to the host

let's

humpback:

localhost> finger ©humpback [humpback]

Login hodges hodges

TTY Idle When co lOld Fri 15:05 pi Fri 15:05

Name Jack Hodges Jack Hodges

Office

finger used without a "name" argument will humpback) for all users and return a list

this case,

tion) currently active

on the

host. In this

poll the host selected (in

of userids (plus informa-

example, the

full

symbolic address for

humpback was not necessary, because the system had an alias for humpback in its "/etc /hosts" table or equivalent. The information that is displayed along with the userid resides

The contents of the

command user

is

name

file

finger

file.

when

are displayed differently

in real

part of their life is

Jim.

finger finger a

the

issued for a specific user. For example, you can also

knowing only

user's

finger

in a

name. For example, suppose you know

that a

Then you can type

localhost> finger jim@sf suvaxl which "Jim"

will

produce a display of finger

files for all the users

in their finger file (i.e., in their userid

or their

tem. In this particular case, seven user's finger

.shown here). si

You could

king information

then try to identify which It

should be noted that

with the string

alias)

on the sys-

were displayed (but not

"Jim"

is

finger

the person

you are

does not guarantee

on the network; however, you will be able to tell when they were logged on and whether they are currently logged on because finger will

thai a user last

for.

files

name

is

finger is that a user may have a different finger file on different hosts. When you "linger a user." every host on which the user has active processes on localhost will display display the user's login status.

A

significant aspect of

7.3 Single-User Status

its "

finger

for the user. Consider the

file

jhodges"

below.

On

the

sfsuvaxl

finger command

231

issued for the user

the finger file looks as follows:

localhost> finger jhodges -« In real life: Jack Hodges Login name: jhodges 338-2335 Home phone: NA Office: TH 970, Shell: /bin/csh Directory: /usr/fl/ jhodges -* On since Jul 18 13:35:36 on ttyqc from modeml3.sfsu.edu login Project: Lets find out what makes this thing tick.

— alias .

Status

Plan:

Assistant Professor (Artificial Intelligence) Computer Science Department Office Hours: T 1-4

whereas the same user has a different account the host

(i.e.

hodges) and

finger

file

on

futon:

localhost> finger hodges@futon [futon. sf su. edu]

Login name: hodges In real life: John Hodges Directory: /Users/hodges Shell: /bin/csh On since Aug 20 15:30:33 on ttyp3 from huckleberry sfsu -* Project: Pull the wool over your own eyes!

-«

,

alias

.

.project

Plan: I plan to use this machine as little as possible, so don't plan on finding out when I log in by using this finger

.plan

-«

file.

I could have used the finger command with "Jack" "Hodges" just as easily as the userid on that host. In both cases, finger displays the login name (i.e., the userid), what is called a name alias (what follows "In real life:"), the user's office location, their home phone, the path to the user's home directory, the path of their login shell, a line

In these examples,

or

"John"

or

describing their

".project."

last login session,

and the contents of two

files,

sponse can be modified/customized by the user with the (Section 5.2.4, page 150) and

chf n

"

.

plan," and

command recommands chsh

All of the information displayed in the finger

232

Chapter 7 Network Processing

Changing Your finger

File

Users can modify the contents of their finger

file

using the

chfn command,

as

shown below. localhost> chfn Changing finger information for jhodges Name [Jack Hodges] Office number [Thornton Hall 970]: Office Phone [338-2335] Home Phone [NA]: :

:

where the bracketed contents, and the In this case,

items are the defaults from the existing finger

( [ ] )

s on

no modifications were made

lows "Name"

the

fills

name

the other fields in the finger

file,

handlers to indicate

who

email

is

some

it

may

bizarre

it,

fol-

like

and many

used by mail

not be very valuable to a

name

alias.

File

.plan and .project how the finger display a message to those who would fin-

There are two user created and configured which, in addition to

ger

in

that often this alias is

from, and

mail recipient to receive mail from

will appear.

The item that The name alias,

need not have your real name

Remember, though,

file

the user.

to the finger file.

alias field for the finger file.

users insert aliases.

The .plan

by

the right indicate the responses given

Both

chfn and chsh,

files are

used to display

files,

determine

you, and can contain whatever text you want to place in them, although a

certain

amount of discretion would be wise. The plan shown for one of my old " plan" files below: .

lines, as

file

can have multiple

.

localhost> cat .plan Assistant Professor (Artificial Intelligence) Computer Science Department Office Hours: T 1-4

This example tion that file

is

is

basically a

form of signature, where

not normally found in the finger

quite elaborate, and

one fingers them.

It

was providing informa.

plan

sometimes even have a program executed when some-

should be mentioned that w hen someone fingers you. they

often just want to find your login

Deluging them with taste,

file.

I

Users often make their

lots

ID or

to find out

when you

last

logged on.

of information could be considered a form of poor

so you should be careful in selecting the content of these

files.

7.3 Single-User Status

The .project The

pro j ect

.

233

File

file is

a shorter, one-line,

file,

as illustrated below:

localhost> cat .project Lets find out what makes this thing tick.

New

accounts are generally given a stock

resident

somewhere

want

modify the information

to

likely

have

to create these files

placed in your

home

.plan and .project which

system other than the user's account, so

in the file

in

your

.plan

and/or

if

.project, you

are

you will

with a suitable text editor. They should be

directory.

Your Login History

7.3.3

One of the

ways to determine a user's usage is with last, last lists the from some date (usually since the last time the wtmp file the present. Each entry in the history looks as follows:

best

user's login history

was deleted)

to

userid terminal host login-date time-on-off (login-time)

last

is

often used to determine whether a user

is

currently active. If the

"time-on-off" and

" login-time) " entries of the last response history cannot be filled in. and will say "still logged in." For example, consider the login history below:

user

is

currently logged on. then the top-most

localhost> last jhodges more jhodges ttyqc modeml3.sfsu.edu jhodges ttyp2 huckleberry sfsu jhodges ttyp7 modeml3.sfsu.edu jhodges ttypO Matterhorn COGNE jhodges ftp toaster.sfsu.edu jhodges ftp sf suvaxl sf su.ed jhodges ttyp3 huckleberry sfsu jhodges ttyp2 oad-8csld. sf su. e jhodges sutro.sfsu.edu ttyp7 jhodges couch.sfsu.edu ttypa jhodges ttyq5 telnet.sfsu.edu jhodges ftp huckleberry. sfsu jhodges Maui.CS.UCLA.EDU ftp jhodges ftp Maui.CS.UCLA.EDU jhodges ftp huckleberry. sfsu

(

|

.

.

.

.

Thu Jul 18 13:35 Wed Jul 17 17:53 Tue Jul Mon Jul Fri Jun Sun Jun Sun Jun Sat Jun Thu May Sat May Mon Mar Sun Feb Thu Feb Thu Feb Tue Jan

16 1

21 16 16 8

30 11 11 24 14 14 29

09:06 23:44 00:30 15:47 13:12 11:37 17:03 14:47 10:22 14:08 13:45 13:43 20:20

still logged in 17:54 (00:01) 09:06 (00:00) 23:45 (00:00) 00:33 (00:02) 15:47 (00:00) 16:57 (03:45) 11:50 (00:13) 17:09 (00:06) 14:48 (00:00) 10:36 (00:13) 14:08 (00:00) 13:45 (00:00) 13:43 (00:00) 20:28 (00:08)

® (2)

(3)

(5)

(5)

wtmp begins Wed Dec 31 16:00

The

login history above

items selected. The history

is

a truncated version of the real listing, with a

shown above

indicates a

number of

few

things about a

2o4

Chapter 7 Network Processing

you look closely at a last response, you can tell what a user's schedwhere they do their work, where they hide, and other good things. Consider the output above. When the history was taken the user was still logged in from modeml3 sf su edu (item 1). The other entries show the amount of user. If

ule

is,

.

.

"login-time" in parentheses (hours:minutes). For example, on Sunday, June 16

"jhodges" logged on

huckleberry

at

at

13

:

12

(i.e.,

noon) for (03:45), or 3 hours and 45 minutes (item

"jhodges"

terhorn

logs in from

[item 2],

many

Maui

1:12 in the after-

3).

Also note

that

huckleberry, Mattoaster, sutro, couch [item 4]),

different hosts (e.g.,

[item 5],

from different networks (e.g., sf su, UCLA), and by different modes (e.g.. direct and modem). Finally, note that "jhodges" logs in at any time of the day between 9 a.m. and midnight, usually for a short amount of time, but sometimes for extended periods.

One

to display all login sessions

note of caution. The

from the

last

last command

time the system

file

is

going

"wtmp" was reHence the use of

many cases, this could result in a very long listing. more above. You could also use the head command, but there are options to the last command so that this isn't necessary. For example, if you use the '-N' moved.

In

option,

where

will

'N' is a

be displayed

number, then only

N

lines of the total

localhost> last -2 jhodges jhodges ttyqc modeml3.sfsu.edu Thu Jul 18 13:35 jhodges ttyp2 huckleberry sfsu Wed Jul 17 17:53 .

7.4

number of

lines

in the response:

-

still logged in 17:54 (00:01)

Network-User Status to look for activity on the network. The more obvious which you are looking to see if specific users are logged in, so that you can get in touch with them. The other case is one in which you are trying to find out what the big jobs are, who is running them, and when they run their jobs so that you can do your work some other time (or on some other host). Either way, it is important to be able to look at the activity on the network and understand what it means. "Activity," in this context, means ( ) the users who are logged in and (2) what they are doing. There are two ways to

There are two reasons case

is

one

in

1

determine activity across the network. The

who

first is to poll

the

machine on

the

The second is to poll the machines on the network for how active they are. These methods can be accomplished with the who. users, and w commands. network

to see

is

active.

7.4

235

Who Is Out There

7.4.1 If

Network-User Status

you already know who a user

is

on the network, having determined

their use-

finger, then a simple listing of who is on the system tells you if they are there or not. You can then decide whether you want to be on the system or not. Two commands are used to poll the network for users. The who command polls the local host for active users. A sample who is shown below for the host localhost: rid with

localhost> who shahryar ttypO vcsc2087 ttypl vcsc2162 ttyp2 arichard ttyp4 rlee ttyp5 fbuenaf ttyp6 davidm ttyp7 vcsc2107 ttyp8 azhao ttyp9 vcsc2095 ttypb vcsc2123 ttypd homelsl3 ttype vcsc2177 ttypf vcsc2085 ttyql goldstei ttyq2 vcsc2014 ttyq3 jchan ttyq4 vcsc2106 ttyq5 pbourne ttyq7 ttyq8 j cheung vcsc2185 ttyq9 chance ttyqa vpcsc4 ttyqb jhodges ttyqc vcsc2105 ttyqd

Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul Jul

18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18 18

09 13 13

11 12 12 10 13 13 12 13 13 13 11 11 12 10 13 13 13 13 13 13 13 13

01 13 12 10 02 49 42 12 01 22 27 38 18 20 22 04 46 28 20 21 26 32 34 35 37

(rincon. sfsu. edu) (hh-3 02dync sf su (bus212dl0 sf su. (gisps2-l sf su. ed (ac-pc2 .sfsu. edu) (oad-8csld. sf su. (

(

.

(

.

{

.

(

(

(lib-el45csla.sfs lib-maccs2a. sfsu (ac-allen. sf su. ed (bus212d21 sf su. (telnet .sfsu. edu) futon. sfsu edu) (oad-8csld. sf su. (lib-maccs2a. sfsu (mdmsrv4 sdsu edu (oad-8csld. sf su. (ac- jchan. sf su. ed (138.202.2.1) (modemll sf su edu (russian. sf su edu (bus212dl9 sf su (net -chance .sfsu. (telnet .sfsu. edu) (modeml3 sf su edu (modemll sf su edu (

(

(

(

.

(

(

.

(

(

(

.

.

.

.

(

(

(

(

(

.

(

.

.

(

(

(

.

.

(

.

.

This was only a partial

list!

The who command

is

output with a simple for-

mat:

[USERID] [TTY] [LOGIN-DATE] [LOGIN-TIME] [LOGIN-SITE] Note

that the user

IDs appear

to

be listed

who

listing

can be useful

random

(i.e.,

when the who command is may be dramatically different.

a host. In contrast,

number of users

in

in

order, since the

TTY, determining how much load

ordered by which device they logged in from

list is

the second field). is

likely to occur

A on

issued on a workstation, the

236

Chapter 7 Network Processing

huckleberry [1 who hodges ttypO Aug 13 14:31 (modeml4.sfsu.edu) ]

The remote who command, rwho, performs

rwho traverses the local network that command on our example LOCALHOST

the

same function

as

who ex-

cept that

the host

this

proves fruitless because

no

local

network

to

which

it is

is

attached

to.

Issuing

has

it

connected:

localhost> rwho localhost>

Conversely, issuing the same

worked

to

many

command from

a workstation

which

net-

is

other (and sometimes heterogeneous) hosts, can be entirely

different:

huckleberry [2] rwho eisman toaster ttypl Aug 13 13:43 :08 Jessica futon:ttyp3 Aug 13 14:23 :01 sheehan walnut ttypO Aug 13 14:02 :

:

In this example, notice that the syntax of the table

is

slightly different:

[USERID] [HOST:TTY] [LOGIN-DATE] [LOGIN-TIME] [IDLE-TIME]

so this

command, when

effective, additionally provides information about

long the user has been idle

command).

(i.e.,

Specifically, the user

how "

j

for about

one minute, so we know

'-a'

option to

(all)

rwho

is

long

it

essica,"

in the table

above, has been idle

that she is currently very active.

issued, all local networks are polled

ing users are shown, again for a workstation

how

has been since the user issued a

hooked up

When

and the

the

result-

to a local network, as

follows:

huckleberry [3 rwho -a eisman toaster ttypl Jessica futon: console Jessica futon:ttyp3 sheehan walnut ttypO sherif futo/ ttypO ]

:

:

:

Aug Aug Aug Aug Aug

13:43 08 14:22 99 59 01 13 14:23 13 14:02 13 09:33 4:35 13

13

Notice that the display for to

on

rwho is different from that of who, but rwho lists the userids, the host the\

and longer than that for last, lo.

similar

logged

the data and time they logged on. and the amount of idle time they have

7.4

had since

their last

command. This

Identifying User

7.4.2

The second command

is

similar to the

Names on

to find out

the

last command

to the

entry.

Network

what users are on the network

is

users,

whoami for a single user, lists the userids of users currently system. An example for localhost is shown below:

which, like

on

237

Network-User Status

logged

localhost> users epearson jason jhodges jkelley ramberg schwartz vcsc2195 vpcsc21

However, when

rusers)

is

issued,

the similar remote version of the

we

see that the

command

is

users command (called

not supported:

localhost> rusers Command not found.

Issuing the

users command on

a workstation provides the following re-

command rusers

now

sult:

huckleberry [4] users hodges and the remote

is

supported:

huckleberry [5] rusers stars. sfsu.e cook carpente gibbs.sfsu.e gronerts esmeralda s f aragons futon. sfsu.e Jessica sherif Jessica walnut sheehan homer. sfsu.e jason lisa.sfsu.ed goel lentil. sfsu. levine bart.sfsu.ed bregler kumquat.sfsu kroll marge. sfsu.e goel quark. sfsu.e ramberg huckleberry hodges .

t

t

host

userids

work, while the remaining items to the host.

For example. Jessica,

sf su edu. This means .

name of a host on the netgiven row are names of users logged on

any row

In this example, the first item in in a

sherif,

is

the

and Jessica are logged on

that Jessica has

two active command

to

shells.

futon

.

-

Also note

2oO

Chapter 7 Network Processing

logged on to both

that user goel is

lisa. sfsu.edu and

marge, sfs-

to

u edu. .

Host Information and User Information

7.4.3

Finally, the

the

w command

w command

is

integrates

an integration of who and

uptime

uptime. As mentioned,

and who. The command displays who

logged in and what they are doing. Below

is

an example:

is

localhost> w — 4:14pm up 9:15, users, load average: 1.04, 1.01, 0.76 User tty from login© idle JCPU PCPU what -* pbourne pO modemll sf su. 4:13pm mail vpcscll pi dh9.uccs.edu 3:59pm 2 2 rn jhodges p2 huckleberry sf 4 06pm w shahryar p3 rincon. sf su. ed 2 :10pm 18 i2 robinson p5 modemll sfsu. e 12:12pm 12 17 -csh jchan 2:08pm 05 -csh p6 ac- jchan. sf su vpcsc21 p7 lib-maccs2a sf 3:18pm vi dis.out -* wkwong -csh p8 oad-8csld. sf su 4:07pm

line 1 like

uptime

,

.

.

:

other lines similar

.

to

who

.

.

As you can

see, the first line is identical to

on the system. Notice

lines represent users

user

is

doing. Very nice!

The columns

w

1

The

Field 2

The name of the

Field 3

The host from which

Field 4

The time of day

Field 5

The number of minutes

Field 6

The

CPU

time used by

Field 7

The

CPU

time used by the currently active process

Field 8

The name and arguments of the

Field

a.

A

the remaining

shows what

the

are explained as follows:

7.1

Table

uptime, while

that the last field

Display field descriptions

tty is a special

user's login

device

file

name tty

a

(userid)

the user the user

is

is

the user logged

logged

in

on

logged on

on

since the user last issued a all

command

processes and their children on that terminal

current process

associated with a terminal

line.

You can force w to display only information for a particular user by issuing command with the userid (e.g., w userid). Because the w command provides such a variety of information, is often the only command used to check

the

it

US(

is

and system

status.

7.5

239

Network Status

7.5

Network Status The commands who and users on

to a particular

ever, all

you

really care to

the network, or the

are excellent

ways

to find out

know

whether a particular host

is

what the processing load on

a particular host

commands ping, uptime and ruptime can be

Sometimes you

will

have a

difficult

performance of the network

that the

In such cases,

is

logged

you

will probably

is

is.

accessible on In such cases,

used.

Host

Statistics for a Specific

7.5.1

who

system and what tasks they are working on. Sometimes, how-

time connecting to a host, or you will find isn't

want

what

might be on other occasions.

it

to find out if the

problem

is

with you or

with the machine you are trying to work with. This can be easily accomplished with the

ping command,

as

shown below:

localhost> /etc/ping huckleberry.sfsu.edu PING huckleberry.sfsu.edu: 56 data bytes 64 bytes from 198.137.218.1 icmp_seq=0 time=5. 64 bytes from 198.137.218.1 icmp_seq=l. time=l 64 bytes from 198.137.218.1 icmp_seq=2 time=l. 64 bytes from 198.137.218.1 icmp_seq=3 time=l. 64 bytes from 198.137.218.1 icmp_seq=4 time=l

huckleberry PING Statistics packets transmitted, 5 packets received, round-trip (ms) min/avg/max = 1/1/5 localhost>

0% packet loss

5

When

the

ping command

is

issued with the

local host sends a data packet to the

make

doesn't is

a difference to the

screeen. This process

for the

[

-r

]

[

remote host

name of a network (it

command), which

host, the

could be the local host,

is

then sent back.

it

A packet

sent every second, and the statistics for each packet are displayed on the

ed by the user

ping

ms ms ms ms ms

-v

is

is

ping command ]

host

continued

until the

number of counts that was requestis terminated. The general format

reached, or until the process

[

is

shown below:

packetsize

In this template, the '-r'

[

count

and '-v' options

tions) will not be discussed here,

man page

]

]

(i.e.,

routing and verbose op-

and the interested reader should see a

refer-

more details (man ping). The host is the required argument to the command, and both the packetsize and the count (the number of transmissions to make) can be provided to the command. For example, the

ence or the

for

240

Chapter 7 Network Processing

previous example could be modified as follows without changing the response:

localhost> /etc/ping huckleberry.sfsu.edu 64

5

The results of a ping command can be very useful to even the novice network user, because it provides network load information. While packets are being sent, each packet has a status line that looks as follows: 64 bytes from 198.137.218.1: t

t

packet size

icmp_seq=0

time=5. ms

.

t

originating nost

The

t

time (msec)

trip

.

count

last item, the trip time, is a

reasonable indicator of the status of the

connection between the two machines (your local host and the one you are

pinging). The of

from the command shows a cumulative summary where the number of packets sent and received are not-

final display

the packets sent,

all

ed, and, importantly, the percentage of packets lost in the process.

huckleberry PING Statistics packets transmitted, 5 packets received, 0% packet loss round-trip (ms) min/avg/max = 1/1/5 5

good indicator of the network connection. When the remote number will typically be 100%. The last value gives an effective measure of the network load, since, over the time it takes to run the number of packets sent, the average load can change measurably. This

host

also a

this

Host Processing Load

7.5.2

When

is

down,

is

a host

formance

is,

is

up and running,

in

terms of

it

is

how many

often useful to look at what

its

actual per-

effective users are running jobs, over a pe-

riod of time. This can be accomplished with the

ample below shows the format which

uptime

uptime command. The

ex-

displays:

localhost> uptime 4:26pm up 9:42, 8 users, load average: 0.84, 0.74, 0.62 k

1

There are ten second lon

minute

5

minutes The

fields in the display.

field tells if the host is

the host has been

up

"up"

(in this case

(i.e., (

>

15 minutes

first field is

running).

the current time.

The

third field tells

and 42 minutes). The fourth

The

how

field tells

7.6

how many

users are active, and the fifth field

the fourth field.

The

sixth

and seventh

is

Remote Processing

a text field

"average")

for the last three fields. Fields eight => ten

ages over the

last

5,

l,

(i.e.,

fields are text fields

and 15 minutes, where load

of users. The following example shows that

"users") for "load" and

(i.e.,

show

the load aver-

measured

is

in the

number

LOCALHOST cannot display load

ruptime, because it isn't on commands rwho and rusers:

information for other machines using

work, as was seen with the

241

a local net-

localhost> ruptime no hosts

!

?

The same command, when issued from

a workstation on a local network

produces a different result and form:

huckleberry [6 nipt ime couch up 6+20:39, cs

futon huckleberry springfield toaster walnut

up 6+00:25, up 5+22:34, up 3+16:03, up 112+13:01, up 99+00:32, up 24+14:07,

1 1

1 1

There are nine

users, users, user, user, users, user, user,

load load load load load load load

fields in this table.

00, 1

00,

00, 1

00,

00,

00,

00,

00,

00,

00,

00,

00,

00,

00,

The

1

first field is

00 01 00 00 00 00 00

the

name of a

huckleberry. The second field tells whether the host The third field tells how long the host has been up. The "N+" as

is

host, such

currently "up."

syntax means that up for "N" days "plus" whatever time follows in hours:minutes format. The fourth field tells how many users are logged on to the host. The fifth field is just the text field (i.e., "user") for the fourth field. The sixth field is the text field (i.e., "load") for the seventh => ninth fields, which tell what the average load (in users) has been over the last 1, 5, and 15 the

host

has been

minutes.

7.6

Remote Processing The notion of multi-user computing environment is associated with the ability to run many shells at once. The system does not know who the owner of each shell process

ular machine,

is,

so any particular user can be running processes on any partic-

and any particular user can be running multiple processes on any

machine he/she can log on

to.

In this section, the different

user can run multiple shells or shell troduced.

methods whereby a

commands on remote machines

will

be

in-

A remote machine is any machine other than the one the user is cur-

The notion of running a shell on a machine which is located somewhere other than where the user is located is called remote processing.

rently logged onto.

242

Chapter 7 Network Processing

Remote processing

the essence of a shared resource network, since a user

is

can run processes on machines which are less heavily loaded as well as on the one where they are sitting. In this section, you will learn how to perform three tasks:

send and receive

•

with other (remote) hosts

remote login to or from another host on a network

•

create and execute shell

commands on remote

hosts

Experimenting with Remote Processing

7.6.1

Because you most this

files

•

chapter

do not have accounts on other machines, and since specifically about performing work on other machines, do not

is

likely

UNIX does not care, when you issue a command, if you are sitting at machine you issue the command from. Thus, if you want to test any of the commands you will learn about in this chapter (except anonymous ftp), you despair.

the

can issue the

command

with the host argument being the machine on which

your account resides. For example, f oobar

.

if

cs oz edu, and you want .

.

you have created lowing command: as

a

" .

rhos ts"

localhost> rep foobar.es. oz.edu: blah

f oobar

you have an account on the host experiment with rep, then (as long your directory) you can issue the fol-

to

file in

.cs.oz.edu rblech

"blah" appear

and you should see a duplicate of the

file

home directory. All of the commands this way (i.e., using your own host as

in this section

File

7.6.2

The

"blech"

in

your

Have

fun!

Transfer Protocol

File Transfer Protocol, or

one machine

a target).

as

can be experimented with

ftp,

is

commonly used

to another without the use of

to transmit files

magnetic tape media,

cially useful for single-file (vs. directories) transfers, so

it

is

ftp

good

is

from espe-

to use with

Tape ARchival (tar) and compress utilities. Some of the command ftp is given below, and more details can be found in the man page (man ftp). the

syntax for

ftp

[

-v

]

[

-i

]

[

host

]

The '-v' option stands for verbose mode, in which case ftp will display it does. The '-i' option turns off interrogation when multiple file transfers are being made (e.g., with mput or mget). Normally when perform-

everything

ing these tasks client host

ftp

will ask for authorization

(machine) that

ftp immediately

ftp

is

to

on each

file. If

communicate with on

the

you specify

command

the

line,

attempts to establish a connection to an ftp server on that

Remote Processing

7.6

host. Otherwise,

from you.

it

typical invocation

command

will enter its

When ftp

is

may

interpreter

awaiting commands,

it

and await instructions

prompts you with

'f

tp>.' The

look as follows:

localhost> ftp huckleberry.sfsu.edu Connected to huckleberry.sfsu.edu 220 huckleberry FTP server (Version 5.18 (NeXT 1.0) Wed Aug 23, 1989) ready. Name (huckleberry.sfsu.edu:): hodges -* 331 Password required for hodges. MY -PAS SWORD ** Password: 230 User hodges logged in. ]

[

243

(T)

@

ftp> Is 200 PORT command successful 150 Opening ASCII mode data connection for file list. .

.

.

DIRECTORY LISTING

.

.

-« ftp> quit 221 Goodbye.

(T)

The user typically is provided with a default login which can be overridden as shown in the example (at item request

is

made and

the user completes the login

in square brackets, 1).

Then

a password

on the remote host (item

2).

commands the user wants to execute, such as 'Is' in this example, the quit (or bye) ftp command is issued to log off the remote host (item 3). Some of the more commonly used commands are described in After issuing whatever

Table

Table 7.2:

7.2.

ftp Command reference

open HOST

Establish a connection to the specified host

pwd

Display the

name of the

cd DIR

«•

Change

the

working directory

to

DIR on

the remote

led DIR

Change

the

working directory

to

DIR on

the local

Is DIR

Display a directory

listing

of

DIR

on the remote machine

lis DIR

Display a directory

listing

of

DIR

on the

mkdir DIR

Make

rmdir DIR

Delete a directory on the remote machine

delete FILE

Delete the fde on the remote machine

get FILE

Retrieve the

a directory

file

ftp

server.

HOST

current working directory on the remote machine

DIR on

the remote

named FILE and

local

machine

machine

machine

machine

store

it

on the

local

machine

244

Table

Chapter 7 Network Processing

7.2:

ftp Command

mget FILES

reference (cont)

Retrieve the specified

FILES from

the remote machine:

FILES

can be

specified with wildcards

put FILE

c=>

Store a local

mput FILES

Transfer multiple local

file

named FILE on files

the remote

(FILES) from

machine

the current local directory to the

current working directory on the remote machine:

FILES

can be specified

with wildcards

send FILE

Perform the same functions as put

status

Show

Invoke a

? command

Obtain help for the

command

binary

Set the

mode

bye, quit

Terminate the

ftp

session with the remote server and exit

close

Terminate the

ftp

session with the remote server and return to the

i

the current status of shell

file

command

One

ftp

on the local machine

transfer

to support binary

image transfer

ftp

of the truly amazing capabilities offered by networked computers

our access to other machines and applications across a network.

ample

I

ftp

interpreter

will present is

trieve files

anonymous

ftp

which

is

used to send

is

One such

ex-

and

re-

files to

from remote hosts where you do not have an account, usually called

public archives.

Copying Archived Remote

Files

Occasionally you might hear of software databases (perhaps in a newsgroup, in

email, or from friends) and want to gain access to the software located there.

you might find yourself looking

for useful information

on

other institutions and other locations.

Many machines have

an

In other situations

machines

at

anonymous ftp

capability that enables users without accounts to log in and

acquire software. Machines with this capability are generally called archives. I

have included the protocol for using

this utility in the next

example.

Remote Processing

7.6

245

localhost> ftp huckleberry.sfsu.edu Connected to huckleberry.sfsu.edu. 220 huckleberry FTP server (Version 5.18 (NeXT 1.0) Wed Aug 23, 1989) ready. -* anonymous Name (huckleberry sfsu. edu: jhodges) 331 Guest login ok, send ident as password. -* Password: [[email protected]] 230 Guest login ok, access restrictions apply. .

(V)

:

[2J

— ftp> Is 200 PORT command successful. 150 Opening ASCII mode data connection for file list.

(T)

bin etc

pub forward .hidden .

.places 226 Transfer complete. 37 bytes received in 0.01 seconds ftp> quit 221 Goodbye.

(3.6 Kbytes/s)

example above, the ftp prompt is "f tp>," and my responses are shown after these, in bold. What I did was to issue the ftp command with a In the

local

machine,

a version of

huckleberry,

"TeX3.0" on

(i.e.,

as an argument.

The procedure

when asked

user ID (at item 1) and,

address

it.

I

already

to use the

typed

I

as

had

your

your mail

"jhodges@sf-

It

listed the available directories (item 3).

anonymous

this host

was not echoed because this login is part of and expects a password. Once I was accepted, I then

(item 2).

the standard login script

knew

"anonymous"

for your password, to type in

userid and host address). In this case,

suvaxl .sfsu. edu"

al,

is

Really quite straightforward. In gener-

users are given severely restricted access to the machine, usu-

ally to specific directories

ample, the directory

I

where public software

have been given access to

is

is

kept. In the preceding ex-

the

"pub"

directory.

To use anonymous ftp to look around on the network, you must know to look. One way to find out where archives of a particular sort are is through newsgroups, at least this is the way it was done until very recently. If where

you were

later

chives for that topic reside.

around.

and subscribe to the appropriate newsyou would see mention of locations where the ar-

interested in a particular topic,

group^), then sooner or

Of

course, this

You

method

could then

still

ftp

to the archive

and look

works, and you can also ask friends

who

might remember where an archive resides. Recently an online database has been developed to keep track of

ftp

sites

around the globe, along with servers to query the database from anywhere on the network.

The

utility is called

archie

and was originally written by Alan

£hO

Chapter 7 Network Processing

Emtage and Peter Deutsch

at

archie

McGill university,

has

become an

valuable aid to help users around the globe locate and acquire software.

It

in-

also

is now a consistently updated command line like any UNIX supported on your host. To do

helps to reduce replication in archives since there

database of

ftp

utility. First

you have

so, use the

archie

sites,

used

is

archie

to find out if

which command

at the is

"archie"

with

as

its

argument:

localhost> which archie /usr/ local /bin /archie

This will work

if

archie

is

located in any directory in your search path.

it may still reside on the system, in which case you might try invoking man page (man archie). If all else fails, you could request assistance from the system administrator. Below is a list of options for using archie.

If not,

the

followed by a simple session using

Table

7.3:

it.

archie Command

reference

-c

A

-e

An

-r

A

regular expression search

-s

A

case insensitive substring search

-1

List

-t

Sort inverted by date

-m #

Specifies the

-h HOST

Specifies the server

-N#

Specifies query niceness level (0-35765)

case sensitive substring search exact string match

one match per

line

maximum number.

#.

of hits to return

HOST

Using these options, you can now access archie and locate an archive site. For example, I have decided to look for no more than five (5) sites which support latex. I use the -m' option to select the number of sites to display, and '

"LaTeX"

I.

Many

systems have

interested users.

a

is

"help"

You can send

want

the string

I

newsgroup

that

is

to search for.

Since

I

did not use an option, the

monitored by the system administrator and other

mail to this address

if

it

exists, or

>ou could send mail

to "root."

7.6

search

is

based on an exact match. Below

is

Remote Processing

the output

24 1

from the command.

localhost> archie -m 5 LaTeX Host cnam.cnam.fr Location: /pub/TeX/TeX3/TeX3 DIRECTORY drwxrwxr-x 512 May 4 1991 LaTeX Host emx.cc.utexas.edu Location: /pub/mnt/ source/ tex/tex-3 14/TeX3 14 DIRECTORY drwxr-xr-x 512 Jan 15 00:00 LaTeX Host ics.uci.edu Location: /mac DIRECTORY drwxrwxr-x 512 Aug 17 04:15 LaTeX Host liasun3 epf 1 ch Location: /pub/tex/tex3 14-imake202 DIRECTORY drwxr-xr-x 512 Aug 16 20:15 LaTeX Host walton. maths ted. ie Location: /src/TeX/TeX3 14 DIRECTORY drwxr-xr-x 512 May 8 1991 LaTeX .

.

.

.

.

.

.

.

There are three

lines in

of the response. The

each response, as illustrated by the shaded portion

on the

the host symbolic address

first line identifies

net-

ics.uci.edu. The second line identifies the directory in which the search item resides, such as "/mac." The third line describes the directory in which the search item resides, which should have the search item in work, such as

its

name. This

will essentially

be the output from "Is

-1' on the directory.

mind that ftp uses the network and that you should use some discretion about when to transfer files from one site to another. Generally speaking, the later the better. Most users agree that anonymous ftp should be used only during nonprime hours (i.e.. 1900 - 0600 hours local time for the remote site, although it might be considerate to select non prime-time hours on both ends of the network, when possible). Bear

7.6.3

in

Remote Copy

Remote copy

is

probably more useful than

ftp

in

some circumstances, be-

cause you needn't actually log on to the remote host to copy a

however,

file;

you must have an account on the target machine. In order to use remote copy, you must have, or create, a file in your home directory named " rhosts." This file must reside on the machine which you wish to log onto, so you must .

have an account on that machine. The tries,

.

rhosts

each of which has a machine address and a

file

list

consists of a

of userids.

list

Any

of en-

user/ma-

rhosts file can rlogin to your account without a password and can use rep to copy files and directories from your account or to your account. As you have probably heard. rhosts files chine combination that exists in your

.

.

are dangerous for system security, because they allow

one of your accounts the potential

to log

on

to other

anyone with access

machines

easily.

to

However.

24u

Chapter 7 Network Processing

there are advantages, and

A rhosts .

file

rep is

one of them.

must reside

in

your home directory, and has a

each user and platform that you want to have access to your account.

dummy

file

line for I

have a

below:

hobbes.cogent.ucla.edu freebie fuzz.cogent.ucla.edu zorch laina.cs.ucla.edu corrigan huckleberry.sfsu.edu smith sfsuvaxl.sfsu.edu cohen f

t

host address

userid Note

list

"zorch"

that user

which the sample but not from other

.

at

UCLA has been given access to the

account in

rhosts file resides when she logs on from the host fuzz hosts. You may want other users to be able to test software

or edit files that belong to you, without the hassle of copying files through other

means. One very important thing about a

.

rhosts

file is that

it

be made readable by others, since they might then obtain access

who

must never to

someone

has privileges to your account. They might also be able to break the pass-

word of someone who has access yours. Using remote copy

is

to

your account even

quite simple, as evidenced

if

they cannot break

by the following

ses-

sion:

localhost> rep -r maui.cs.ucla.edu: /usr/lib/tex/macros sf suvaxl:Texmacros

This example illustrates the coping of the entire tree

(i.e.,

recursively) from the host

macros" host as

"macros"

.

.

sf suvaxl. The colon ) is used after each template below. You need not be logged on to either ma-

directory on the host

shown

in the

directory sub-

maui cs ucla. edu over to the "Tex(

:

chine to perform this task, as long as your userid exists on both systems in a .

rhosts

file:

rep flags hostlrpathl host2:path2

and

When you really rep all the time.

you end up using

way.

It

UNIX

just turns out that,

you

will

probably use

when you have

kinds of machines to do

it.

and

rlogin

lots

of work to do.

rlogin

enables you to

commands on any machine as though you are sitting at the madirectly, telnet is similar to rlogin, but I will present a session any-

execute shell chine

all

get rolling with

Remote Processing

7.6

249

Remote Login

7.6.4

r login stands tem looks

for

"Remote LOGIN." When you

into a file called

"/etc /hosts"

chine) that you name. If you have a

.

issue the

command,

the sys-

(or equivalent) for the host

rhosts

file

and entry on

that

(ma-

machine,

then you are logged in as though you had logged into that machine directly. If

you do not have a rhosts file and entry on that machine, then you are asked for your password on that machine, and. if you provide it correctly, you are .

logged on. the

I

will first

show you how

to use

it,

and then

I

will describe

some of

commands:

localhost> rlogin sfsuvaxl.sfsu.edu -1 jhodges last login: Thu April 18 17:36:16 from huckleberry sfsu ULTRIX V4.1 (Rev. 52) System #2: Thu Jan 17 11:53:02 PST 1991 You have mail sf suvaxl> .

command

This

could have been issued without the "-1

jhodges' and

it

would have worked, but it would have asked for a password. For the purposes of this example I created a rhosts file. With that file I was able to log in .

without using a password. Notice .

login and cshrc .

that, as

soon as

I

execute the

command, my

on the host sf suvaxl execute and the new

with the standard output on

my

local terminal.

Once you

shell is run

are logged

on

to the

remote host, you can perform any task that you can perform from that account

when logged

in directly.

hence your path variable,

etc.. will

that the shell scripts

which

are run,

and

be those on the target machine.

telnet

7.6.5

telnet same

Remember

as

is

very similar to both

rlogin. and

ence between

telnet

the syntax

and

rlogin is

rlogin

and ftp. The functionality

is

the

very similar to ftp. The primary differis

that

no

.

rhosts

file is

used/required

telnet. On the other hand, you cannot use rep (or rsh) either. When you use telnet, the entire login script will be executed, so you will be for

prompted

for both

your ID and password. Consider the sample session and

commands shown on

the next page.

^DU

Chapter 7 Network Processing

localhost> telnet sfsuvaxl Trying 130.212.10.102... Connected to sfsuvaxl.sfsu.edu. Escape character is ,A ] Ultrix-32 V3.1B (Rev. 10) (sfsuvaxl.sfsu.edu) login: jhodges Password: Last login: Thu Apr 18 17:37:14 from huckleberry sfsu ULTRIX V4.1 (Rev. 52) System #2: Thu Jan 17 11:53:02 PST 1991 You have mail. sfsuvaxl [1] '

.

.

Should you not succeed will

In such a case the

Table 7.4:

in

logging on to the machine of choice,

'telnet>' prompt following commands will be useful:

communicate with you with

telnet Command

Open

close

Close a

quit

rsh sfsuvaxl -1 jhodges Is F90/ Mail/ README. TeX3.0* TeX3 .0/

TeX3.0.tar* bin/ core*

localhost>

local terminal,

and

quits.

is

as-

Notice that

have access will

need

to

to.

have provided the remote host name, the account which

I

is

I

command to execute. To use rlogin and rsh. you rhos ts file on the remote machine with an entry for you.

and the

have a

because there

251

System Management

7.7 File

.

no request

for a

command

note that, after the

password from the

shell using this utility.

has executed, control

Also

returned to the shell on

is

localhost.

7.7

File

System Management All network users have the responsibility to maintain their accounts in such a

way

as to optimize resources for all users. This

to clean

be able

up

after yourself

and back up your

to generate statistics

on your

means

that

files regularly.

local host

you should be able To do so, you must

(where your directory

is

ed), as well as

network-wide. In general, you should strive to eliminate

your director,

that are

if

unneeded. such as binaries not being used regularly

the binaries are being used regularly, the source files.

need both

at the

".log." ".bbl."

same

and

time.

".dvi"

As an example,

You

or,

generally do not

latex files ending with ".aux."

can be removed since they are produced as a result of

tex compilation. These and other

cussed already. In

locat-

files in

this section,

you

commonsense

guidelines have been dis-

will be introduced to utilities for obtaining

information about your disk space allocation, your usage of disk space, the sys-

tem overall usage of disk space, and two

utilities for

managing your personal

system.

file

Account allocation Disk free space Disk usage

7.7.1

File

and directory archival

File

compression

Account Allocation

Each account can

potentially be allocated a specific disk space limit.

system administrators invoke disk space

amount of disk space allocated

to

limits, and.

when

Not

all

they are used, the

accounts varies with institution, with depart-

ment, and with users. There are two important things to remember about ac-

count allocations (or quotas):

and current usage with the allocation increased

if

(

1

)

that

you can determine what your quota is and (2) you can possibly get your

quota command,

you can

justify

it.

The quota command is invoked under different circumstances. You may to see how close you are to your limit before trying to transfer a large file

want

You might also want to check your quote before executing which might exceed your quota, because you may lose some of your work. The easiest way to find out is to issue the command.

on

to

a job

your account.

2o2

Chapter 7 Network Processing

quota [user] where user represents a userid and

mand

is

is

When the comown userid, as il-

an optional argument.

issued without a user argument, the default

your

is

lustrated below:

localhost> quota Disc quotas for jhodges (uid 326) Filsys current quota limit fwarns /usr/fl 94474 95000 100000 /usr/cp2 19 95000 100000

quota

will return a table

being used on the various

quota

files 4438

limit

#warns

10

showing what your allocation

is

and

how

it

is

systems your account current has disk space us-

file

and a limit which is generally set to 5you exceed your quota, then you will be notified at not be allowed to perform tasks that would increase

age. Generally an account has a quota

10% beyond your quota. the terminal and

you

If

will

your disk space usage.

Table 7.5:

quota

Field description

Filesys

The

file

current

The

current disk space usage on this file system (in 1024 byte blocks)

quota

The

user's quota on this file system

limit

The maximum disk space

#warns

The number of warnings

files

The number of files using

system for which allocation

is

being reported

limit for user

that

on

this file

have been posted

system

to the user

the current disk space

Display Free Disk Space

7.7.2

Users can determine the current status of mounted drives on the local host with the

df command. A mounted device

is

knows how

drive or a tape drive, which the computer

with

it

a device file

tecture are

df has and

and a

encouraged

local directory.

to take a

space

is

Those

available, as

tile

to address

interested in

course speciali/ing

displays a line tor each mounted

how much

a peripheral device, such as a disk

in

computer

in

archi-

the topic.

system, telling how

shown

by associating

Table

7.6.

much space

it

7.7 File

Table 7.6:

df

System Management

20o

Field description

Filesystem node

Location and name of associated device

Total kbytes

Total (unformatted) space for the device

Kbytes used

How much

of the space has been used

kbytes free

df Filesystem Total node kbytes /dev/raOa 15551 /dev/raOd 201919 /dev/raOe 201919 /dev/raOh 257407 /dev/rala 7423 /dev/rald 201919 /dev/rale 201919 /dev/ralh 265575 /dev/ralf 404127 /dev/ra2a 7423 /dev/ra2d 201919 /dev/ra2e 201919 /dev/ra2h 265575

The

kbytes used 7514 127494 15061 168621 3

21216 14029 184084 299980 10 597

101245 189453

kbytes free 6482 54234 166667 63046 6678 160512 167699 54934 63735 6671

181131 80483 49565

df command

is

shown below:

used

Mounted on

54% 70%

/

8%

73% 0% 12% 8% 77% 82% 0% 0% 56% 79%

/usr /var /usr/users /usr/rala /usr/sl /usr/s2 /usr/cpl /usr/fl /usr/ra2a /tmp /usr/f2 /dba

entry in the table always represents the device

©

file and file system from which you are issuing the command. Thus, the host is associated with the device "/dev/raOa." All devices which are attached to (mounted on) the host are associated with such an entry. Notice, on the far on." This entry means that the device right, the column titled "Mounted which is associated with device file /dev/raOa is mounted on the local directory "/" (item 1). Thus the drive associated with the device file /dev/ first

for the host

254

Chapter 7 Network Processing

raOa is the root how much space

the device can hold.

in kilobytes (i.e..

thousands of bytes) and usually refers to an unformatted ca-

disk, or root volume.

The second entry in the table indicates capacity. The value is measured

i.e.. its

pacity rather than an actual

(i.e..

dev/raOa) has 15, 551 of which 6,482 bytes are

kilobytes, or 15

By issuing home directory space

is

a

(i.e..

megabytes of

can determine on which device your

Then you can look

on the device

total storage space,

46%).

pwd command, you

resides.

available

free

usable) capacity. In this case, the slash disk (/

df

in the

table to see

The

that includes that directory.

how much

third

column

how much space, in kilobytes, is currently being used on the device. For example, the "/dev/ralf " device (item 2). on which my directory resides (/ usr/f 1). has a total capacity of 404, 127 kilobytes (i.e.. 404 Megabytes). and 2 99,980 kilobytes (300 Meg) are being used. The fourth column tells how many kilobytes are still available, and the fifth column gives that value as tells

a percentage of the total disk space on the device. Notice that these

do not add

up.

When

a device

is

formatted,

some of its space

generally reserved, and this accounts for the discrepancy.

reaches 100%. no users will be able to execute any

age of additional space until some

which

director} subtree

commonly low

mentioned

with the device

file in

mounting point

the first entry. This

7.7.3

du

is

is

is

The

last entry- identifies is

for the device. All directories be-

on the device associated

how you

will find "your" device

pwd command.

Finally, note (item 3) that there

but

10%)

commands requiring the us-

files are deleted.

in this entry physically reside

system associated with the "/tmp" ers,

say

the utilization

associated with the device on the system. This

referred to as the

the one

with the

is

(e.g.,

When

numbers

is

is

a physically separate device

director}'.

This space

is

on

this file

writable by

all

us-

being used,

du

for temporary, rather than permanent, storage.

Disk Usage similar to

df insomuch

as

it

tells

how much

storage

is

amount of Disk Usage" and will display the disk space takdirector}'. For example, if you want to know how much space

stands for "display

en up by a local

your

localhost> du

home

directory uses, type the following:

-

An example "

jhodges".

is

shown on

the following page for the director} of the user

7.7 File

System Management

200

localhost> du /usr/f 1/ jhodges/bin 171 /usr/f 1/jhodges/tmac /usr/f 1/ jhodges/mail-elsewhere 9 /docs /manual 120 /usr/f 1/ jhodges /TeX3

2

.

3

/usr/f 1/ jhodges/TeX3 0/usr/spool /usr/f l/jhodges/TeX3.0/usr /usr/f l/jhodges/TeX3.0 /usr/f 1/ jhodges/News /usr/fl/jhodges/AKCL /usr/f 1/jhodges/Mail /usr/fl/jhodges/lib /usr/fl/jhodges/F90 /usr/f 1/ jhodges/Texmacros /usr/f 1/ jhodges /Manual -in-LaTeX /usr/fl/jhodges/Archive-TEX /usr/fl/jhodges/Code /usr/fl/jhodges/MX-TESTS /usr/fl/jhodges/LATEX-TESTS /usr/fl/jhodges .

15040 15167 2

27551 728 1067 33

362 2649

31654 11965 3

34

91746

(T)

du will display an entry for each subdirectory below the directory where the command was issued. The display will use full paths. Thus, the "TeX3 0" directory is listed as "/usr/ f 1/ jhodges /TeX3 0" (at item 1). The du command displays directories In this example.

I

have spared you the entire

list,

.

.

from the inside

out. or deepest to shallowest.

Thus, the

last

term

in the display

of any particular directory will show the space used by that directory subtree.

For example, the

last line

of the

TeX3

.

directory (item 1) has as

its first ar-

"15167," which stands for 15,167 disk blocks, or 15+ megabytes. Each of the following entries shows the value for the home director)' (the others were omitted for the sake of brevity). The last entry is the space used by the directory originally called with the command (tilde expands to "/ usr/fl/jhodges"). which is a soaring 91+ megabytes. This is an excellent example of a disk hog. Not a nice term, and maybe not so deserved, since this I am responsible for the port of a number of utilities to the host SFSUVAX1 You can use the du command to keep tabs on your own directories and maintain them as necessary by deleting files or decreasing their size with the tar

gument

and

1.

1

the value

compress

utilities

presented in the next section.

This means that the block size on this device

is

1024 bytes, or

1

kilobyte.

2o6

Chapter 7 Network Processing

7.7.4 I

and Directory Archival

File

have noted

will

that

ftp

As ftp can

files

take a while to send large

or directories over to a remote machine. files,

and cannot send directories

except file-by-file, one must use other methods with

Tape ARchival (tar) of

files

tar key

[

a

is

method

onto magnetic medium.

from one machine

blocksize

[

]

where the keys

to another.

name

]

ftp to

at all,

achieve such ends.

originally designed for efficient archiving

It is

also

commonly used

The standard form

for

tar

to

move

directories

is

files

are described

defined better in the

However, often you

useful for sending a file or files.

is

be interested in sending large

below and the blocksize and name arguments are

tar man

page. Generally, the use of

tar

will

be as

fol-

lows:

localhost> tar cvf tarfile.tar filenames localhost> tar xvf tarfile.tar

The a single

first

file

command

will take the files (or directories)

"tarf ile tar." The .

'c'

and put them

all

onto

key means create an archive. The sec-

same order, ownership, and protection starting in the now-present location. The 'x' key means to extract the contents of the archive. A sample session is shown below, followed by a description of the keys that can be used. It should be notin the above examples is a verbose key which eched for emphasis that the

ond

line will then take

them out of the

tar file

and place them

in their

V

oes everything that tar does. The 'f ' key

be the name of the

tar

file to

tells

write the files

tar to.

that the next

argument

will

7.7 File

localhost> cd tmac; Is tmac Xref ieee ditroff tmac. Xref pic tmac.Xtra psroff tmac tmac.Xtras tmac tmac Franz tmac an tmac tmac. an. new tmac.XP tmac an6n tmac.Xalg tmac.an6t tmac .Xref .acm localhost> tar cvf tmac. tar * a ditroff 272 blocks a pic 272 blocks a psroff 18 blocks a tmac. Franz 3 8 blocks a tmac.X 16 blocks a tmac.XP 2 blocks a tmac.Xalg 2 blocks a tmac .Xref acm 5 blocks .

tmac ayday tmac. bib tmac cp tmac syb tmac imagen tmac os tmac tmac tmac scover .

.

.

.

.

.

.

.

.

.

System Management

257

tmac.sdisp tmac skeep tmac.srefs tmac.vcat tmac vgrind .

.

.

.

.

.

.

(T)

(2)

.

localhost>

Because the

V option was used

displayed on the monitor as ?

chived there file.

it is

is

an 'a in the

command

(at

item

1),

each

file is

file ar-

column (item 2), followed by the name of the name, and this number represents the size of the

first

A number follows the file When

in this

being archived. Notice that for every

command has completed, every file in the "tmac" di"tmac tar." The files are not removed, copies have been made and put into tmac tar. Also note that I used the wildcard

file, in

rectory

blocks. is

now

copied

the

in the file

.

.

(

*

)

to

denote

TOASTER,

all

to

items in the directory.

demonstrate

how

Now I will create a directory on the host

to extract, or "untar," files using

tar.

258

Chapter 7 Network Processing

localhost> ftp toaster other responses omitted ftp> mkdir tmac 257 MKD command successful. ftp> cd tmac 250 CWD command successful. ftp> pwd 257 /Users/hodges/tmac" is current directory. ftp> binary 2 00 Type set to I. ftp> put tmac. tar 200 PORT command successful. 150 Opening BINARY mode data connection for tmac tar 22 6 Transfer complete. local: tmac tar remote: tmac tar 237497 bytes sent in 1.6 seconds (1.4e+02 Kbytes/s) (

.

.

.

.

.

.

1

"

(2)

(3)

.

.

.

ftp> Is 200 PORT command successful. 150 Opening ASCII mode data connection for file list. tmac tar 226 Transfer complete. 12 bytes received in seconds (0.012 Kbytes/s) ftp> quit 221 Goodbye. .

localhost>

In this example.

item

1).

and cd

I

ftp

to the host, create a

to that directory.

new

Notice (item 2) that

director)' for I

my

files (at

used the binary option

more reliable file transfer, even when the file isn't binary. If the file is binary and you send it in ASCII mode, then you end up with a corrupted file and you may be able to extract some, but perhaps not all. of the files in the tarfile. Once in binary mode I issue the with ftp.

I

find that this option provides a

put command (item 3) to transfer the tarfile. Now. after ftp logs me out. I go r login in to toaster (procedure not shown, but notice the different C shell prompt) and

I

can type the following.

7.7 File

System Management

259

toaster [1] cd tmac; Is tmac tar toaster [2] tar xvf tmac. tar x ditroff, 139264 bytes, 272 tape blocks x pic, 139264 bytes, 272 tape blocks x psroff, 9184 bytes, 18 tape blocks x tmac. Franz, 19444 bytes, 3 8 tape blocks x tmac.X, 8113 bytes, 16 tape blocks x tmac.XP, 841 bytes, 2 tape blocks x tmac.Xalg, 639 bytes, 2 tape blocks x tmac Xref .acm, 2317 bytes, 5 tape blocks .

.

toaster

[3

When place the

logged on to

I

files.

Had

I

toaster.

created the tar

created the directory where

I

file

I

wanted

to

with embedded directories, they would

fly when I untar the file on toaster. Then I change direc"tmac" and untarred the file. Here are some of the keys used with tar

be created on the tories to

on a

Table 7.7:

common

basis:

tar Options command

c

«

Create a

t

List the

X

new

archive

names of

Extract the

reference

the files in the archive

all

named

items from the archive;

recursively extracts the directory and

£

FNAME

The key must be followed by want

V

tar to

a space

ceded by a function

file

-

.

tar

it

contains

name of each

in the

what

file

it is

is

archives or extracts, prefile

that

to that

(cd todir; tar xv

command,

it

doing with the

you can copy the contents of a user diof another. The syntax follows, but you man page for tar.

system (disk)

can find the example

In this

a directory, tar

and the name, FN/aME, of the archive you

letter that indicates

nifty thing about

rectory on one

cd fromdir; tar cvf

is

and subdirectories

read from or write to

This option makes tar display the

One

one of the items

if

all files

the first part of the

-

)

command

gets

you

to the directory

2b0

Chapter 7 Network Processing

The second

command

you want

to archive.

to create

and archive with the 'f option, but the

stands for the standard output.

Now

part of the

The

files selected are

the results are piped into another

cating to the

new

issues the tar

selected

file

those in the

"

command sequence

command '-'

is

which

.

"

directory.

that starts with lo-

directory and ends by extracting the archive from the stan-

dard input. Note that the verbose option

is

being used throughout so the user

can watch the progress of the transfer. 7.7.5

File

Every once

Compression you look

in a while,

at a tarfile

cide that you are simply using too conscientious. This files to a

much

and

it

a time for file compression,

is

more compact

version, and replaces the file

in a smaller file.

press "tmac tar"

and see what happens, but

its

original size so that

of

compress:

we can

tell if

compress name with

For example, we could

compression resulted .

looks enormous, or you de-

disk space and want to cut

first

we

down

to

be

compresses

"file.Z" if the try to

com-

should take a look

at

anything good results from the application

localhost> Is -1 tmac* -rw-r r 1 jhodges 471040Apr 18 14:19 tmac tar localhost> compress tmac. tar localhost> Is -1 tmac-* -rw-r— r— 1 jhodges 237497Apr 18 14:19 tmac. tar.

—

.

original copy of tmac tar is 470K bytes and the compressed 237K bytes. You can see that using compress amounts to quite a

The sion

is

.

ings in space. The next question that you might ask is "HOW FILES BACK!" Simple: type uncompress tmac tar .

prompt

ver-

sav-

DO GET MY I

at

the

C

shell

as follows:

localhost> uncompress tmac. tar localhost>

Notice that you do not need to provide the for

uncompress. The tar and compress

chives, since

and then use

it

is

" .

Z," as

it

is

the expected suffix

utilities are naturals for file ar-

far easier to transfer a single, smaller file

uncompress

and tar,

over the network

locally, to restore the archive.

7.8 Exercises

7.8 Exercises

and Sample Quiz Questions

261

and Sample Quiz Questions

7.8.1

Exercises

Exercise

1

Using your own directory as

a source

and

target, try the

rlogin.

telnet, ftp, rep, and rsh commands. Find an anonymous ftp site

Exercise 2

and bring something small back to your local

Issue the

host.

who, rwho. uptime, ruptime, and w commands. Note

their differences.

Exercise 3

Practice

file

system management by tarring and compressing a

file

and

a directory, and then reversing the process.

7.8.2

Problem

Sample Quiz Questions 1

List three different real

Problem 2

name

is

ways

to find out information about a user

Dr. Jerk Foobar, assuming Dr.

Explain what tar.

Problem

3

is

compress, and uncompress

why. What are the options •

Foobar

are used for and

to

create an archive

•

view the contents of an archive

•

extract an archive

What is the minimum set of commands, and their correct order, to anonymously log onto a host named sumex-aim Stanford edu, .

.

retrieve a file in binary format,

and exit?

Problem 4

Approximately how much space

Problem 5

What UNIX command do you use named cl3.1.2.tar?

Problem 6

whose

logged on.

is

saved using

compress.

to list the contents

of a

tar

archive

LOCALHOST. You have an account on the [email protected]. and have a ".rhosts" file. You want to retrieve the files in "/usr/lib/tex/ inputs" to a directory called "texinputs" at localhost. What command(s) do you issue from your terminal and fuzz? You

are logged onto the

host

Problem

7

Which of the following provides the most explicit information about a Which is the fastest way to find out if they are logged on? Which is the fastest to find out how long they have user and what they are doing?

been idle? •

who

•

rwho

•

users

•

rusers

•

w

•

finger

•

last

262

Chapter 7 Network Processing

What does

Problem 8

notion of

file

resource environment?

regard and

this

You

Problem 9

X

are

how can you

system management mean and

system management

file

why

Which

in

your day

to

apply the

day use of a shared

four utilities are particulary useful in

are they useful?

working with a Computer Science faculty member

to port

an

VAX. The tared and compressed file takes up 6 and the uncompressed directory uses 16+ Megabytes.

server to the

Megabytes,

Assuming your

Which

•

likely

faculty

member

has access to these filesystems,

filesystem(s) in the

want

two

listings

to try to bring the server

•

Why?

•

Which UNIX command produced

below would you

least

up on?

these listings?

A:

Filesystem node /dev/raom /dev/raoa

Total kbytes 15551

kbytes used

7423

3

Total kbytes 201919 265575

kbytes used

kbytes free 6482 6678

7514

used 54%

Mounted on /

0%

/usr/raoa

used

Mounted on

B:

Filesystem node /dev/ratn /dev/raon Problem 10

597

189453

You

are logged onto the

task,

when

the time

the screen goes

way

kbytes free 181131 49565

SFSUVAX1.

0%

79%

/tmp /nonl

doing some minor processing

between what you type and what gets echoed on up. After a

few minutes, reponse time returns

to

normal, only to become sluggish again, and again, over the entire period

you

•

What

•

How

type of problem you think it is you would identify what type of problem this is What one could do to avoid this from happening in the

•

7.9

are logged on. Please identify

future

Recommended Reading UNIX

References

Sobell.

Mark, [1989]. A Practical Guide to the UNIX System, 2nd Ed., Benjamin-Cummins. Redwood City. CA.

Advanced UNIX Rochkind. Marc

J.

Principles

[

1985].

Englewood

Advanced UNIX Programming,

Cliffs, NJ.

Prentice Hall.

PART II Programming Languages and ANSI C The intent of this part of the book is to introduce the student to the concepts associated with programming. You are not expected to become fluent in C, nor are you expected to become a good programmer by writing a few simple programs. However, you are expected to learn how to write a program, which includes proper code presentation, debugging, and function. You are also expected to learn the concepts in programming that are applicable to any programming language. No aspect of the C programming language is presented in very much detail. Generally, a topic is introduced that covers a broad range of programming situations. An example is discussed that illustrates how that topic fits into the programming environment and how it is used. Throughout the chapter the example will be modified to add to its functionality. Where alternative approaches are possible, the alternatives will be tabulated so that you can modify the example code to experiment with them. By the end of each chapter, you should have a few template examples that enable you to construct simple working programs that exhibit behavior commensurate with the topics leading up to and including those introduced in the chapter.

Introduction to

C Programming

8.1

Introduction and

Scope

Programming is an empirical skill of writing instructions to control a computer. Programming is both rewarding and fun. but you will never understand a programming language without writing and correcting (i.e.. debugging) computer programs. In this chapter, the C programming language will be introduced, along with methods for writing, compiling, executing, and debugging simple programs. In subsequent chapters, more complex notions will be introduced which will enable you to write programs that can perform more elaborate tasks. The following topics will be covered in this chapter: •

Programming languages

•

The C programming language

•

A

simple

•

C

language operators

C

program

At the conclusion of this chapter, you should be able to look at a C program how and why it is laid out. You should know how the file is named, how a compiler is invoked to translate it. and what the executable file and understand will be called.

You

should understand the differences between syntax and se-

mantics of a programming language, and you should

and semantics of C. Finally, you should that

know how

make use of simple expressions and

know some

of the syntax

to write simple

C

programs

variable assignments.

265

266

Chapter 8 Introduction to

8.2

Programming Languages

C Programming

A programming language is a set of rules for evaluating instructions to a A computer program is a set of instructions (like a recipe) the

computer.

computer follows

to

perform a specific

task.

An

instruction can be as simple

as a variable assignment or a call to a function. Expressions are combinations

of operators and their operands (data).

A

programming language

consists of

operations on data, and the rules for combining and evaluating the resulting expressions.

The

instructions

which comprise a computer program can be exI am conveying to you can

pressed in different languages just as the thoughts

(spoken) languages. The underlying concepts grammar and style for expressing concepts change. The essence of programming is to understand the underlying concepts that are be-

be expressed

in different natural

are the same, but the

ing expressed, and to recognize

how

they are captured in any particular pro-

gramming language. There are different kinds of programming languages. The computer hard-

ware manipulates

electrical signals,

and the instructions which

tell

the

comput-

machine language. Machine language is appropriately called a low-level language. It is both awkward and unnecessary to communicate in low-level languages. Most programmers com-

er

what

to

do with

electrical signals are called

municate with the computer with high-level languages such as LISP,

FORTRAN,

or

PASCAL,

C,

COBOL.

The computer cannot execute directly. They must first be

the instructions of these

programming

lan-

machine language. The translation process is called compilation. The translation is performed by another program, called a compiler, which reads the expressions from the guages

translated into low-level

high-level language, interprets them, and rewrites them in machine language. The executable expressions of a computer program are called code. A program in a high-level programming language has two code components: source code and object code. Both source code and object code reside in files. The source

code

file is

the editable version of the

The object code er programs,

8.2.1

is

file is

program and

is

the file that

is

compiled.

the translation produced by the compiler, and, for small-

often the executable version of the program.

Programming Language Syntax and Semantics

A

programming language evaluates expressions by first recognizing the symbols which comprise expressions. Once recognized, the symbols can be clustered together into meaningful units, which the computer can then execute. The symbols and their organization into expressions is called the language's syntax and grammar, whereas the interpretation and meaning of expressions is the language's semantics. Writing a successful computer program requires an understanding of the language's syntax and semantics.

The C Programming Language

8.3

Grammar and

Syntax

The compiler must read

a

program according

These rules are called grammar it

267

rules. If the

and consistent

to specific

compiler

is

rules.

able to read the data,

can then use these rules to construct, or parse, the data into recognizable ex-

pressions, interpret their meaning, and continue the translation.

To

parse ex-

pressions, the language expects certain symbols to have specific meanings. For

example, the language must be able

to

when

determine

the

end of an expres-

It must recognize the end of expression character. Likewise, each language has a specific character sequence which it recognizes as a comment,

sion occurs.

after

which

symbols

is

it

does not

try to parse

meaning. The interpretation and order of

which

a language's syntax. Programs

rules will not

compile and will produce

errors.

violate a language's syntax

Programs with syntax errors

cannot be executed because the compiler never succeeds in creating the object

code

file.

Structured Languages

A structured language has an extensive syntax and grammar. The more structured a

programming language,

sult, the errors (or

easier to find and

the

more grammar

rules

it

will have.

bugs) detected by the compiler during translation

debug

(resolve).

guages: however, their advantage

is

The opposite a freedom

is

from

As a remay be

true of unstructured lan-

strict rules for

how expres-

programming languages have their advantages, but this is an issue which is best addressed by a course in programming language design. C is considered a structured programming sions are presented. Both structured and unstructured

language, because

it

has a rich syntax, although

it is

less structured than, say.

PASCAL.

8.3

The C Programming Language C

is

a versatile language, and

ware platforms, meaning computers with the

ANSI C

little

that

its

structure enables portability

programs written

or no modification.

standard. Although

ANSI C

We is

in

will

C

between hard-

can be used on different

be using examples based on

not currently the most portable ver-

new. it may become the most porThe language will be introduced by looking at some simple examples which illustrate some of the language's syntax in proper pre-

sion of the language, because

it is

relatively

table version in the future.

sentation format (called style). Following the examples will be an introduction

C

to

operators,

program compiling, execution, and debugging.

C

program

•

Writing a

•

Basic syntax of a

•

Compiling a

•

Executing a

C

program

C program C program

268

Chapter 8 Introduction to C Programming

Before tive.

we

begin,

should be reiterated that C,

it

like

UNIX,

is

case sensi-

This means that lowercase and uppercase characters are unique and are

not interpreted as having the same meaning in any context. For example, an is different from "TOTAL" or "total." When you use you must be very careful to reuse it exactly the way it was

identifier such as "Total"

a variable name, originally used.

8.3.1

Writing

Programming to

how

it

style

concerns

how

a

program

presented visually, as opposed

is

executes. Style includes comments, format, and object

ventions, none of

guidelines

Ch8

C Programs

is to

which

affects

how

make programs

a

naming conprogram executes. The purpose of style

easier to read, so that

programs can be used

properly, fixed, updated, and rewritten in different languages by different people at different times. Consider the following properly written program,

"UNIX/Ch8 /First

.

c,"

which

is

nothing more than

comment

lines

and an

empty program:

Figure

8.1

Use

:

of input parameters in First.

/••••••A*************************************************/ First.

AUTHOR: DATE: /* FUNCTION /* APPROACH /* COMMENTS

J.B. Hodges August, 1993 NONE NA Demonstrates the use of banner comments for program documentation.

*/

/* /*

/* /

©

*/

/* FILE: /*

*/

*/ *

*/ */ */

******************************************************** /

int

main (void) {

return

(

)

This example program does nothing

mally necessary to

start

do with the program and comments are being made. have nothing

to

at all,

but

it

illustrates

programming. The numbered items will

what

in the right

is

mini-

margin

be used to identify lines where

Banner Comments Even an empty program should have some statement indicating what it is intended for. Although it is not a formal component of a computer program, a program's documentation plays a crucial role in how the program is present-

The C Programming Language

8.3

ed. In the

program

in Fig. 8.1. item (1) is called a

269

banner comment, and

is

comments. Ever}' programming language has a mechanism for making a comment, which is a line of text that is not parsed or evaluated in any way by the compiler. In C. comments are delimited by /* at the beginning and */ and the end. and can span more than one line. The banner comprised of a

series of global

comment shown This

is

has

comment opening and

partly for readability, as the reader

closing characters on each line.

need not search for the end of the

comment, and for security, since the programmer can delete a cidentally removing a comment's beginning or ending.

The banner

itself

line

without ac-

contains information which documents the program's de-

main function banners, etc. Each banner

sign and implementation. There are different kinds of banners:

or program banners, function banners, header

file

documents the aspects of the program specific to its associated procedural component. A list of information which is commonly placed in a main and other function that is

banner comments

provided

is

shown below.

in the banner, the easier

program was intended

to

do and how

it

it

In general, the

more information what a

will be later to understand

was done.

FILE: The most obvious part of the banner should be the name of the pro-

gram or in

file.

In the

example above,

which the source code

FILE LOCATION:

It is

resides.

easy to lose

the

program

"First

files,

and

tify the location in the banner, in case

.

is

it

named

is

after the file

c"

good idea to idena hard copy but not

often a

someone has

the soft copy.

VERSION sion

and DATE:

When many

program

iterations of a

number and modification

exist,

then ver-

date are important data to maintain in

the banner.

AUTHOR

(account ID): The person

should always get credit for

it.

who

designs and writes a program

The account ID

only important to

is

lo-

cate the files later.

CLASS and INSTRUCTOR: er,

the

CREDITS:

This

is

clearly academically motivated;

same mechanism could just

If

as easily

an algorithm or code segment

grammer,

it

is

only

common

is

work

howev-

for department, etc.

borrowed from another pro-

courtesy to give them credit for their

work.

PURPOSE: What

the

program

is

supposed

to do.

and should be a component

of eveiy banner comment. Purpose, or function,

program takes

METHODOLOGY how

it

is

as input

and what

it

is

generally what the

produces as output.

(algorithms/theories used):

What

the

accomplished need not be differentiated

program does and

in

simple programs.

2LJ\j Chapter 8 Introduction

to

C Programming

mechanisms invoked

In complicated programs, the

gram's function

FORMULAS: Where source code

up

may

not be at

appropriate,

it

is

much

the equations/logic being

if

good

to

achieve a pro-

obvious and should be documented.

all

easier to follow someone's implemented are documented

where the equations were found. Otherwise, even the author may forget what is being implemented and where it was found, making corrections, updates, and extensions diffront.

It is

also

to cite

ficult.

VARIABLES which

and

PARAMETERS: A

created, the scribed.

parameter

When

is

an input/output variable

program banner is main function's variables should be declared and de-

specific to a function.

is

When

a function banner

is

the primary

created, the function's parameters

should be identified as input, output, or input/output parameters dition to their declaration

and description.

ables/parameters in a banner than inline because all

the documentation

is in

IMPLEMENTATION NOTES: a

implementation

Even mentioning

USAGE:

may

reduces clutter and

the

methodology or algo-

not be explicit enough to re-

program was developed, so

may

it

one place.

rithms used to implement a function

member how

in ad-

better to describe vari-

It is

specific

comments on

the

be appropriate.

In function banners, a

sample function

call

could save a

lot

of time

Programmers often forget how a function was supposed to be used, so providing an example of its use on legal data, and naming the function(s) which call it, is often later appreciated. One way to provide later on.

a usage

comment

is to

provide the calling function (say, in square

brackets) followed by a sample function call with real arguments.

A

banner should be obvious and

clear.

A box

is

used

in the

example ban-

ners in this text to clearly distinguish documentation from source code, and the horizontal lines of asterisks provide clear boundaries between these sections,

making

the documentation and the associated source code easy to locate.

There are actually two types of comments, of which banner comments are used for documentation. There are also inline comments which you will see

embedded within the source code, often for debugging purposcomments can be problematic in C. because the language doesn't support comment nesting (i.e.. comments within comments). If you have com-

soon, which are es. Inline

ments inside the source code, and you decide to comment out (i.e. block out) a section of the source code, then you have to specifically edit out the comment characters within the block. sible,

much

By

placing as

many comments

of this type of problem can be avoided.

into banners as pos-

The C Programming Language

8.3

2#

1

Program Blocks Every

C program

is

comprised of a main function component and additional

function components

C

ponent of every

when

appropriate.

gram. In every other respect main structure

The main function

program and coordinates

which performs a

like

is

whose

task,

is

a required

com-

the procedural elements of the pro-

any other function.

definition

is

A

function

is

a

semantically comprised of

component blocks: 1 a header. (2) declarations, and (3) statements. The header block is used as an interface to other programs or functions through argument passing. The declarations block identifies the objects and processes which will be used. The statement block consists of the expressions which will be executed by the program. Although the simple program presented above will do nothing, it is a legal C program: it has a single main function which has a header, declaration, and statement block. three

)

(

case on a line by itself, is a declaration. what type of value a variable or function can take on. Every object or function in C can have a type. An object, such as a number or a character, always has a type. For example, an integer is the type

Item (2) in Fig.

A

declaration

int. and a

real

"int."

8.1.

in this

a definition of

is

number

is

the type

A

double.

function in

C

is

a procedural

which can be called with arguments and can return a value. In mathematics, square root is a function which takes a number and returns its square root. A C function works the same way. and the language

construct, like a program,

know what

needs to

kind of value will be returned. The reason

tions, like square root,

human its

can be embedded

use makes sense in the expression. In

may

before

C programming, the

"main" simply means

that

C

func-

value returned by

to help the

embedded in. and this programmer find errors. The

main

a kind of function that will re-

not be appropriate for the expression

can be checked during compilation

is

mathematics, the

and (hopefully) knows whether

interprets the result of the square root

a function

int

in expressions. In

that

is

it

is

value. turn an inteser "&*

Item er.

As mentioned,

functions.

"main" and the

is

It

is

the

says

done through what

identifies this as the

always required

program and

pear as

"main (void) " header identifies how a

(3). the line that

it is.

in a

is

called

C

program,

interfaces to other programs.

in the figure.

delimits the parameter

There

list.

ration,

nor a

is

The

void

in the

function's head-

parameter

list.

The

string

It is

organizes other components in

The

string,

"main." must ap-

and the open parenthesis,

it

set

of parentheses next to

a single item

A void in a parameter list is

parameters for the function.

main

function interacts with other

its

main

though not shown that way rameter

the

primary or organizational function of the program

and there can be space between

list.

is

void

in this particular pa-

simply a statement that there are no

a matter of style. Neither a

parameter

list is

al-

main

void

as a decla-

required by the language semantics.

However: both make sense because they declare

to the compiler,

and

to

anyone

272

Chapter 8 Introduction to C Programming

who reads the program something which Items (4) and

source code what the programmer's original intent was,

often lost in the documentation.

is

open and close curly braces

(6), the

( {

and

}

comprise the

)

statement block for the sample program. Although the only expression in this

segment

is

a return statement, this

is still

the use of statement blocks like this

You

a legal statement block.

when stubbing

will see

discussed in Chapter

is

9.

Each function can return a single value to the function or environment it was called, as specified by a return statement. Item (5) is a return statement, and specifies what value will be returned by the function main. Since no function called main, the value is returned to the environment which called the program, namely the UNIX command shell. This particular from which

return the

of

int is

statement returns a value of 0, which

(i.e.,

is

(and must be) consistent with

integer) type associated with the function's definition.

chosen because the information sent back

to the operating

associated with "success." In general,

teger)

is

turn

statement in

that

main

is itself

example programs,

all

a function.

I

ments and, where appropriate

embedded

A

what value

function,

will use

sequence of statements

A

of-

negative in-

(e.g., 0, 1,

will adhere to using a

re-

only to remind the programmer

to signify success in

main

return state-

to the interpretation of a return statement of an

will use a

I

if

we

is

program executed

ten used as an error function, to signify whether or not the successfully. Operating sytems will vary in

The value

system

1,

is

because

C

views

1

as a "true" logical value.

often grouped together functionally, called a

is called a compound statement. In C, the beginning and ending of a functional context, such The as compound statement sequences, are marked with curly braces { } open curly braces after the "main" function header denotes the beginning of

functional context.

sequence of executable statements

).

(

the context of the function, and

Because

this

program

is

balanced at the end of the context. marks the end of the function.

is

tional context, the closing brace

not intended to do anything,

we

In a func-

will not

show

it

being compiled or executing. In future examples, the compilation will be

shown

if it illustrates

a facet of

programming which

will be valuable to the

novice. In most cases sample input and output will be provided.

Simple Program Statements: Display Information

Now

that

you have seen

a

program

that

works, but does nothing,

statement which does something and see what

it

takes to

pose that you want to display a greeting to the user of

would add

a printf

C

make

this

function to our sample program as

it

let's

add a

work. Sup-

program, then you

shown

in Fig. 8.1.

8.3

Use

Figure 8.2:

of input

in

273

FirstOut.c

FirstOut.c

/* FILE: /* /* AUTHOR:

(Y)

*/ */

*/ J.B. Hodges */ August, 1993 */ Displays a string */ Uses stdio.h function library Demonstrates the use of the I/O function */ */ library and the printf function on a */ simple string.

/* DATE: /* PURPOSE: /*

parameters

The C Programming Language

LIBRARIES:

/* COMMENTS: /* /*

/*****•**************************************************/

©

#include int

main (void) printf "\nHello there future ANSI C wizard! \n\n" (

return

(

(4)

)

0)

}

This program. "FirstOut c," will print the line "Hello there future ANSI C wizard! " by itself and stop. Nevertheless, it introduces four .

new

concepts: (1) the inclusion of standard libraries, (2) the use of standard

functions, (3) the executable expression,

and

(4) the expression terminating

The notes labeled item (1) and (2) in the margin of the program inchanges to the banner which result from the change in program name

character.

dicate

and functionality.

To

use the printf function, which clearly was not written in this program

(or there

would be

a function definition for

it), it

is

output

I/O or 10) and resides in

(called

"stdio h"

must be made available

one of many functions which

program, printf

a

is

to this

associated with input and

library

stdio h

of functions called 1

header file and represents a standard library that is provided with the C programming language, but, like other libraries, it is not made available to the programmer's environment unless the programmer specifically requests it. The request is done .

or "standard input and output."

with the include statement. Item (3)

is

.

is

called a

a type of header statement, because

defines an interface between the current program and other programs. called an include statement, and the

clude

1.

A header file

is

so

statement

named because

it

is

called a

pound sign

(#) is required.

The

#

it

It is

in-

precompiler directive, because the inclusion of

includes the function headers for each function in the library.

2 #4

Chapter 8 Introduction to C Programming

this library

must be performed before the source code

in the file is

compiled.

Other precompiler directives will be introduced and discussed as their functionality merits. Although not shown that way, there can be space between the

pound sign and

the the string

ed to the program, to

Firs tOut Item (4)

is

.

"include." When

c for local use. One of these functions

list,

is

no exception: although

printf is

many arguments, depending on what required argument

any

set

The

it

is

is

identified

it is

results

items which are to be printed,

In the

used to display strings

it is

sample

told

re-

it

argument but may have

programmer

is

The The number

trying to dispay.

by the contents of the control

string.

A

seen as a single object.

argument, interprets

where and how the if

string dictates.

its

con-

Each of

the

any, must be identified in the control string

to print.

printf function call, printf is not instructed to display

items, only the string ever,

the

printf function takes the control string

and displays the

and told how

As

of numbers, characters, spaces, and special symbols delimited

by double quotes. As such,

tents,

is printf.

a string, called a control (or format) string.

is

of additional arguments is

add-

is

available

associated with a type and has a pa-

turns nothing to the program, printf takes at least one

string

made

the application of the printf function, called a function call.

previously mentioned, every function

rameter

the include statement

of the functions in the stdio library are

all

how

any

"Hello there future UNIX wizard!" How-

to print the string, with the special characters

(\n) in front

of the string and the two (\n)s in back of the string. These characters have special

meaning

first

one simply moves the

in the control string: to print a line

feed or carriage return. The

print position to the first character of the next line

before printing the string, and the last two print a blank line after the string.

Were we to print a variable using printf. the variable type and formatting commands for printing the variable would have to be included in the string, as well as the name of the variable as a separate argument. Before compiling and running this program,

let's

look

at

some of the other options

for controlling printf.

8.3

Table

8.1

The C Programming Language

2/0

printf formatting options

:

\n

=$

Print a line feed

\t

=>

Print a tab

%d

=>

The argument

is

%c

displayed in decimal notation

=>

The argument

is

displayed in character format

%s

=*

The argument

is

displayed in string format

%£

=>

The argument

is

displayed in fixed point format: [-]mmm.nnn

%e

=>

The argument

is

displayed in floating point format: [-]m.nnne [±]xx

%g

=>

Display

in

%f or %e

format, whichever

is

shorter

printf "There were %d rainy days in the U.S. last year\n" (

control string with one integer print argument

printf

At the end of the semicolon

many

(

;

other

Long

integer variable

statement in the example (item 4) there

is

a

). The semicolon is the expression terminating character in C (and programming languages). Every line inside the statement block

must begin or terminate lon.

foo)

,

lines

a functional context or be terminated with a semico-

can also be extended to the next

line

with a backslash character

(\).

Compiling a

8.3.2

Since the program the compiler

C Program

FirstOut

now and

.

c will actually do something,

let's

introduce

slowly talk more about the compiler as more complicat-

ed examples are introduced.

The

C

compiler

we

will use

is

the

Gnu C compiler and

is

invoked (on

this

command gcc. We will use this compiler because it ANSI C. Many other C compilers exist, and the program-

particular host) with the is

compatible with

mer should find out about the characteristics of their compiler and related utilities. The compiler takes a file as a mandatory argument, as shown below. The general template for compiling a source file is shown below

gcc

[options]

sourcef ile

.

.

where "sourcef ile"

1.

Traditionally, readable

program code

is

is

the file

name

containing the program you have

called source or source code.

276

Chapter 8 Introduction to C Programming

The name of the

written and wish to compile.

template to compile

this

FirstOut

.

file

must end with

"

c." Lets use

.

c.

localhost> gcc FirstOut. localhost>

where no options are used, and the "sourcefile" command argument used file "FirstOut c." A few other compiler options are listed below.

is

the

.

Table 8.2:

-bsd

gcc Compiler options BSD semantics

=>

Enforce

-g

=>

Produce additional symbol table information for the debugger

-I DIR

=>

Specify the directory

-o OUTF

=>

Name

-0

=>

Uses the object code optimizer

-P

=>

Returns a count of

-v

=>

Compile verbosely

-Y ENV

=>

Compiles

strict

DIR

to search for # include files

the output object file

for

If there are

outf

how many

times each routine

environment ENV

no compilation

(e.g..

BSD,

errors, the next

is

called

POSIX,

SYSTEM_FIVE)

response will get a shell prompt

without any other notification. Unless otherwise stated, the compiled version of the code (the object code), which, in this case, called "a. out." After the

This

is

program

is

also the executable

file, is

compiled, you are ready to execute

is

it.

done by entering "a out," along with any arguments required by the .

program, as follows:

localhost> gcc FirstOut. c localhost> gcc ./a. out

Hello there future ANSI C wizard!

It is

possible that you could

fail to

get the

program

to execute

you have successfully compiled the program. This could happen

even though

if

your

UNIX

/a out" in it. In this case, simply type out" to tell UNIX what directory the executable is in. If you want to change the name of the executable file to something other than a ou t.

execution path does not include

.

"

'

'

.

.

instead of "a.

.

you can use the "-o" compiler option as follows:

localhost> gcc -o foe FirstOut. c

This will

name

the object

code

file

for

"FirstOut

.

c" to be "foe." Be

The C Programming Language

8.3

careful to not confuse the small 'o' with the large '0,'

option to optimize the compilation.

Do (man gcc)

which

for

is

277

the compiler

more information on

compiler options and their applicability.

Errors Detected During Compilation

8.3.3 If

your program doesn't compile, then

is

one where you have

it

has syntax errors in

it.

A syntax error

either typed something incorrectly or have added or

gotten to add something which

is

required by the

C

for-

language syntax. Often

these errors will be displayed on the screen. Errors will be identified by line

number. The

line

number

curs, since the error

is

in the error

flagged

when

may

not be the line where the error oc-

the error

is first

identified.

But

it

should

FirstOut.c program is called Fir-

be close. As an example, consider a slight modification to

which generates a syntax

stOut Figure 8.3:

An

.

c but

is

error,

in a file called

shown below. This

"FirstBug

intentional syntax error injected into

.

c":

FirstOut.c.

localhost> cat FirstBug. /A*******************************************************/ /* FILE: /*

FirstOut.c

/* AUTHOR: /* DATE:

J.B.

*/ */

Hodges August, 1993 /* PURPOSE: Displays a string /* LIBRARIES: Uses stdio.h function library /* COMMENTS: Demonstrates the use of the I/O function /* library and the printf function on a /* simple string. /**********************************************

*/ */ */ */ */ */ */

^

— ERROR

#include void main (void) {

printf

("

\nHello there future UNIX wizard! \n\n"

)

return; }

where the terminating portion of the banner comment lation

produces the following

localhost> gcc FirstBug. Id: Undefined symbols:

main

list

of syntax errors.

(*/) is

removed. Compi-

2# O

Chapter 8 Introduction to C Programming

where, in this case,

many

we

are lucky. In

many

cases, a simple 'typo' will result in

downstream of the error. This effect is called error propagation. There are two types of syntax errors: ( 1 ) warnings and (2) fatal errors. The difference between them is that warnings are recoverable but may point to a problem with the program logic. A fatal error will produce non-executable code. Errors have a tendency to propagate. One error early in the program may cause other errors further along. For example, if you have a missing left parenthesis, you might generate two errors - one for the missing left parenthesis and one when the compiler finds the right parenthesis. Because of error propagation, it is a good idea to correct the first error that occurs, compile the program again, and see if other errors disappear. errors

You can want

to

fix

bugs (called debugging) by editing the source

keep different versions of the source code when you

to avoid destroying a partially will

be addressed in Chapter

1

Many programs

start

You may

debugging,

working program. Techniques for debugging .

Using printf to Request Input and Reading

8.3.4

file.

require the user to type data which

It

requested by the pro-

is

gram. Anytime a program interacts directly with a user, regardless of the inter-

mode, the program

action

is

called an interactive

program. Programs which

are called and perform their function without interaction are called

batch pro-

grams. Inputting large amounts of data is tedious and programmers generally avoid interactive input of large amounts of data; however, for small amounts of data type

it is

some

all right.

We

will

now modify Firs tout

data to be read and then displayed.

.

c to signal the user to

The C Programming Language

8.3

Use

Figure 8.4:

of input/output functions in

279

First io.c

*****•> /* FILE: /*

FirstlO.c

*/ */

/* AUTHOR: /* DATE:

J.B. Hodges August, 1993

*/

(T)

*/

Reads user's initials and number of dogs */ /* */ and then prints them on one line. /* LIBRARIES: */ Uses the stdio.h function library /* COMMENTS: */ Demonstrates variable declaration. /* */ Demonstrates use of scanf on char and /* */ int variable types. Demonstrates use of /* */ printf to output variable values. /****************************•***************************/ PURPOSE:

/*

tinclude int

main (void) {

char first, middle, int ndogs;

last;

/* /*

Initials of user's name */ */ Number of dogs

(3

printf (" \nPlease type your initials, separated by no spaces: scanf "%c%c%c" &first, &middle, &last) printf (" \nPlease type how many dogs you own: "); scanf ("%d", &ndogs) printf (" \nHello, %c %c %c, you own %d dogs, right?\n\n", \ first, middle, last, ndogs);

" )

(4

;

(

,

return

(0)

}

I

mention once more

will

function, so

I

that

I

have changed the name of the

file

and

have modified the banner statement accordingly. Henceforth

its

this

kind of change will be assumed to be important but will not be mentioned. This

program

is

essentially identical to

FirstOut

.

c

in that

no new

libraries are

needed and we are only using standard (sometimes called canned functions). However, we are now using variables, since this program will ask the user to type

some data and

til it is

used.

that data has to

We are

use the scanf function. Finally, ables. Item (3)

is

(i.e.,

stored in

memory) un-

we

we

will

will use the printf option to display vari-

a variable declaration. In C, variable declarations define both

the type of variable that

it

will be

the type precedes the identifier, so identifiers

be remembered

also going to read that data from the keyboard, so

and

its

char

identifier.

is

As

previously mentioned,

the type associated with the variable

first, middle, and last, and int

is

the type associated with

2o0

Chapter 8 Introduction to C Programming

ndogs. Variable names should always be chosen to be The variable names in this example are at least pos-

the variable identifier

functionally appropriate.

remember, but they are slightly cryptic. When variables are cryptic it possible to forget, later, what they were for. This makes reading code some

sible to is

time in the future since the tice that

difficult.

This

is

when an

comment may

inline

be of value,

programmer can write what the variable means and what it does. Nothe comments line up left and right. This simply makes the comment

is not required syntactically. In general, this type of comment may save some space, but confuses the distinction between documentation and source code. It would be better, and cleaner, to have the variables de-

easier to read, but

scribed in the function banner. For the purposes of saving space, only, variables in our examples will be It

documented

inline.

should be noted that variable names have thus far been simple character

combinations.

meaningful

legal to use an underscore (_) to separate characters into

It is

and

units,

numbers

to use

name with

gal to begin a variable

names; however,

in variable

a number, nor

is it

Also notice

also

It is

Item (4)

though

printf

tions, printf

tion or

all

is all

is

on the same

line,

sepa-

right as long as they are all the

right to type

illustrates the

use of the keyboard reading function, scant. Al-

and scant are both I/O functions, they are different kinds of func-

always displays

program which

calls

its

result

it.

As

scant always assigns a value and

not le-

same type (i.e., them on separate lines. You can declare diftyped variables on the same line, but not separated by commas.

char). ferent

that there are three variables declared

by commas. This

it is

any other spe-

name.

cial characters (e.g., $, >, gcc -o fsioc FirstStringlO.c localhost> fsioc Please type your name: Jack Please type how many dogs you own: 2 Hello, Jack, you own 2 dogs, right?

When

the

%s format

used

is

input for the program, as

is

encountered. Thus

"Jack"

is

reasonable

shown above, but "Jack Hodges" would not

be.

Input from a Separate Function

8.3.6

One

scant, characters will be placed into the

in

string variable until the first space

final

use of the scant function

the overall function of the

is

program

fined") into smaller (at least,

more

in a separate function. In is

most programs,

broken down ("decomposed," or

specific) subtasks.

fined into yet smaller subtasks. This approach

may

"re-

and these are further

re-

continue until a subtask

nothing more than a single expression. At that point the program

is

is

constructed

by defining the required variable types and identifiers, and setting up interfaces between each of the subtasks and the top-level function, main. This process is called iterative refinement.

When programming

subtasks are implemented

using constructs which control the flow of execution, this process ciated with

what

is

called

of modular programming control behavior.

As

single exit point.

AC

is

function

is

a control stucture. or module:

AC

Although

wise to use only one. so a

is

it

is

it

defines and

function has a single entry point

than one exit point,

is

feature

such, the structure should have a single entry point and a

in the function header.

The use of functions

also asso-

the use control structures that have predictable

orders a sequential block of statements.

it

is

modular programming. The predominant

possible for a

C

C

function to have

function

is

more

also a module.

as one type of control structure in the refinement process

called procedural abstraction.

To

introduce the notion of modular programming, using functions,

we

will

write a small program which does exactly the same thing as the FirstIO c program: however, the display and input segments of the code will be consid.

ered separate functional subtasks and will be performed by their tions.

One

function

(PrintVals)

will

own

func-

be an output function, which will do

284

Chapter 8 Introduction to C Programming

nothing more than display the final results, and one function

be the input function, which obtains data

in the first place.

(GetArgs)

will

The main function

will coordinate the activities of the functions.

Modular programming for simple

Figure 8.6:

I/O in

FirstModio.c

/A*******************************************************/ /* FILE: /*

FirstModlO.c

AUTHOR:

/*

J.B. Hodges August, 1993 Reads user's initials and number of dogs and then prints them on one line. Uses stdio.h function library. Input is separate from MAIN. Output is separate from MAIN. GetArgs: reads the input data PrintVals: displays the output Demonstrates modular design for I/O with functions.

/* DATE: /* PURPOSE: /* /*

APPROACH:

/* /* /*

FUNCTIONS:

/*

COMMENTS:

/*

*/

*/

/*

*/ */

*/ */ */ */ */ */ */ */ */

#include

void PrintVals (char argl, char arg2 char arg3 int arg4) void GetArgs (char *firstp, char *middlep, char *lastp, int *ndogsp) ,

,

©

int

main (void) {

char fi, mi, int nd;

la;

(2)

GetArgs (&fi, &mi &la, &nd) PrintVals fi mi, la, nd)

(3)

,

(

return

(0

,

;

)

}

This program

that

is

proach

from other programs which have been

FirstlO.

c.

The

difference

(i.e.

requesting

and reading This

a large departure

each of the component subtasks of the original program

presented so is

is

far,

but performs the

input,

same

task as

and printing the values) are placed into separate functions.

an example of procedural abstraction. Although the function-based apinitially

involves an increase in program complexity, the overall sav-

ings tar exceeds the pain. Generally, procedural abstraction three ways:

(

1

1

is

advantageous

in

readability. (2) testability, and (3) modularity.

The main function has two new

declaration components, called function

The C Programming Language

8.3

prototypes

(at

item

which declare the function

1).

their order. This allows the

the file and allows the

like

type, parameter types

and

placement of the function definitions anywhere

programmer

A function's prototype

program.

2oO

is

a lot of flexibility

simply a copy of

when implementing

its

in

the

header, but terminated

an expression.

The

variable declarations

shown

at

item (2) correspond in a one-to-one

fashion with the paramter declarations in the function definition and function call (item 3).

Modular programming

Figure 8.6:

for

simple

I/O in

FirstModio.c

(cont.)

*/ PrintVals: Prints output variables */ INPUT: first, middle, last, ndogs /* OUTPUT: */ None /* RETURN: */ None /* USAGE: */ [main] PrintVals fi mi, la, nd) /••••A***************************************************/

/* /*

(

void PrintVals (char argl

,

char arg2

,

;

,

char arg3

,

int arg4)

{

printf

(

"

\nHello, %c %c %c, you own %d dogs, argl, arg2 arg3 arg4 ,

,

right?\n\n"

,

\

)

return; }

/************************************•*******************/ /*

*/ Reads input variables */ None */ first, middle, last, ndogs */ None */ [main] GetArgs(&fi, &mi &la, &nd) /•************************************************•******/

GetArgs

/*

INPUT: /* OUTPUT: /* RETURN: /* USAGE:

,

void GetArgs (char *firstp, char *middlep, char *lastp, int *ndogsp)

(5

{

printf (" \nPlease type your initials, separated by no spaces: scanf "%c%c%c" firstp, middlep, lastp) printf (" \nPlease type how many dogs you own: "); scanf ("%d", ndogsp) (

,

;

");

(6

return; }

Clearly, each function

and the code

The code

is

is

shown above has fewer

lines of executable code,

specifically associated with the task of the particular function.

easier to read, because

you need not search around for the code

2o6

Chapter 8 Introduction to C Programming

segment that performs the subtask you are looking for. When you design programs using functions, you can initially write the statement block in main that calls the functions, the header and a blank function statement block (called a stub) for each function, and the associated function prototypes. This enables you to compile the program, and to develop the internal workings of each function at

own

your

pace.

Debugging and testing is easier, because you can isolate from the rest of the program. Finally, changes to the

the effects of the function

function need not require changes to the entire program, nor do the other func-

need

tions really

to

know how

a subtask

is

solved as long as the values that are

communicated between functions work together In general,

effectively.

you should work toward developing programs which make use

of modular programming methods and procedural abstraction. The

first

thing

you should notice about this sample program is that each function has its own banner comment. The banners associated with a function are different that

than those for a program, usually shorter. Unless a function

is

undergoing a

amount of revision, it will generally just require a banner that tells what the function name is, what it does, what its input and output parameters are, and what it returns. Sometimes, a sample call is useful in the function banner. In our examples, the function from which this function is called is included in the sample call, in brackets. This can be good for small programs; however, if a function is later used in a library, or if the number of functions in which a large

function

used

is

which can

is large, it

might be misleading

really only be resolved

to the reader.

This

is

an issue

by the programmer.

you look closely at the three function definitions you will see that they follow the same general form: ) the function is declared, (2) the parameter If

all

( 1

list is

defined, (3) the local variables are declared, and (4) the statements are

elaborated. Because

main has

thus far had no parameters, the parameter

lists

GetArgs and PrintVals appear much more elaborate. On the other hand, GetArgs and PrintVals are our first examples of functions which is the return no values. Such a function is declared as void to signify that of

it

programmer's intention statement for

is

to return

no values. The associated function return

simply terminated instead of providing

it

with a value. In item

(4).

we PrintVals. A param-

example, instead of having 4 variable defined within the body of main,

now have 4 eter

list

variables declared in the parameter

list

of

simply declares the items which will be shared between the calling

function and the function being called, and sets up an interface for doing so.

The only requirement maintained.

When

to the interface

the function

is

that the

PrintVals

of the variables used as arguments

in the

We

PrintVals

function parameters.

function from

main. PrintVals does

is

parameter types and order be called from

main,

the values

function call are copied into the

say that the values are passed into the not change the values of these vari-

ables in any way. so they are called output

parameters and

PrintVals

is

2u I

The C Programming Language

8.3

called an output function.

GetArgs (item 5) is somewhat GetArgs starts with no variable

different than for

variable values from the keyboard, these are called input

parameters and

The parameter

list

for

PrintVals. Because

GetArgs

is

values and reads

called an input function. In this case, the variable values are

completely different than those

in

main, because they do not have values

until

GetArgs. Moreover, since these variables will actually be the rescanf function, which returns the location of a variable in memory

they leave sult

of a

GetArgs

rather than the value itself, the parameters in the to

locations of those variables in

the

GetArgs must address

is

be used

in

is

the parameters of

GetArgs,

as objects, a simple

not adequate. Thus the parameters declared in the

commonly

GetArgs

header

referred to as pointers.

A

declared by placing an asterisk in front of the paramter name, after

the type declaration.

More on

this in

as a pointer, then the associated

Chapter

argument

variable with an address-of operator, & call to

memory. Since

expressions within

are 'objects that represent addesses,'

pointer

header must refer

GetArgs

(at

9.

in the .

When

a parameter

is

declared

function call must refer to the

This

is

how

the arguments in the

item 3) are given.

Item (6) shows that the variables associated with the values read in

GetArgs must be declared in main, because the values are returned by GetArgs to main before they are sent into PrintVals. This is called variable reference or call

by reference. Anytime

a function references a value,

it

must declare an object for the value. Notice that the variable names are not the same in main that the parameter names in GetArgs. This is quite all right, because the consistency check

is

based on the type declaration and order of

variables in the function call with parameters in the parameter the

arguments sent

to the function

when

matter what they are named. The program

it is

"Firs tModIO c"

run below:

localhost> gcc -o fmioc FirstModlO.c localhost> fmioc Please type your initials, separated by no spaces: JBH Please type how many dogs you own: 2 Hello, JBH, you own 2 dogs, right?

1.

This

is

list.

As long

called are consistent,

true for simple variables, or scalars. but not so for array variables.

.

is

it

as

doesn't

compiled and

2uO

Chapter 8 Introduction to C Programming

8.4

C Types,

Operators, and Expressions

In the

C programming

language, a program

is

comprised of processes and ob-

A process is comprised of the three component blocks mentioned previ-

jects.

ously (header, declaration, and statement blocks). tity, in

that

it

A

performs a task.

A

process

is

dynamic en-

a

process performs a task by executing state-

A program, a function, and examples of processes and each has its own identifier. An object is a data item, and also has a label or identifier. A constant and a variable are examples of programming objects. ments, which involve the manipulation of objects. an operator are

all

The program examples

that

have been presented so

far

make use of

dard library functions. Although the functions that are provided

in

C

stan-

libraries

are very useful, they are provided as support and cannot solve problems. In or-

der to write meaningful programs, programmers must learn their

own

the

FirstIO

program

FirstExpr first is

own

variables, write their

tions. In order to introduce the

.

c

.

c

to

expressions, and develop their

concepts in

this section,

we

become "FirstExpr c" .

illustrates a

how

few things

that

to declare

own

will further

(see Fig. 8.7).

were mentioned before. The

the declaration of a global (program- wide) constant (item 1)

A

func-

modify

named

constant

is

an object whose value does not change during the course

of execution, and

is

declared using the

"PI."

the # stant,

include

syntax. There

PI can be used

in

is

#def ine

no semicolon

syntax, which

is

after the definition.

similar to

As

expressions and as a function argument, but

it

a con-

cannot

be on the lefthand side of an assignment statement.

The second item of

interest is the variable

can use an underscore, as done

at

item

(2), to

naming convention

make an

in C.

You

identifier easier to read

more descriptive, but care should be taken not to confuse cases, not to use numbers as the first character, and not to use other special characters (such as or

$, &, *,

\,

#).

For example:

int state_tax;

is

a legal variable identifier, whereas:

is

not a legal variable identifier.

int state*tax;

8.4

C Types, Operators, and Expressions

Simple variable assignment expressions

Figure 8.7:

in

289

FirstExpr c .

/************•*******************************************/ /* FILE: /*

*/

AUTHOR

/*

*/

FirstExpr. J.B. Hodges August, 1993 Calculates the volume of a cylinder and

/* DATE: /* FUNCTION:

*/ */ */

*/ displays cylinder characteristics. */ /* LIBRARIES Uses the stdio.h function library /* COMMENTS */ Demonstrates variable declaration. */ /* Demonstrates constant declaration. /* */ Demonstrates variable assignment. /* */ Demonstrates field format specifier. /**********•*********************************************/ /*

#include ttdefine PI 3.14159

©

int

main (void) {

char obj_type; double radius, height, cyl_area, obj_volume;

printf ("\n**** THIS PROGRAM CALCULATES THE VOLUME OF A CYLINDER" \ ****\n\n" printf (" \nPlease input the following information for the cylinder:" "

)

\

"\n\n")

printf (" \tradius scanf("%lf", &radius); printf (" \n\theight scanf("%lf", Sheight); printf (" \nYou have entered the following: \n\n" printf ("CYLINDER RADIUS: %6 3 f\nCYLINDER HEIGHT height) :

"

)

:

"

)

)

.

cyl_area obj_volume

= =

:

%6.3f\'n\n", radius,

\

radius * radius; height * cyl_area; PI

*

(5

printf ("The volume of the cylinder is: %6.3f\n", obj_volume) return

(6

(0)

we have placed four floating point identifiers height, cyl_area, and obj_volume) on separate lines Also note

that

(i.e.,

radius,

in the

program

290

Chapter 8 Introduction to C Programming

same declaration. This was done comments could have been placed to the right of these

(item 3), but they share the

for readability. In-

line

declarations. Item

(4) illustrates the

Item (5)

ment

is

use of a formatting directive, first

t for printing tabs.

use of an assignment statement.

used to define the value of a variable, and

equal sign symbol ( = ).

some

our

illustrates

\

expression,

ting the value

it

When you

means

on the

assign-

always associated with the

see a variable name, an equals sign, and then

that the variable

right. It

is

An

on the

left

of the assignment

get-

is

doesn't matter whether the item on the right

is

a

number or a complex expression. Whatever the expression evaluates to will become the new value of the variable on the left. Only variables can be assigned values; however, they can be reassigned new values over and over again. It should be noted that an assignment statement is not the same as an equation. In mathematics,

on the

is

left

left

hand side

what

hand is

is

on the

identified

tional relationship, right to

the assignment

symbol

as

left.

PI

*

radius

*

to

You

you can

The assignment statement

l_area

right side of an equality

is

identified with

what

programming languages; however, what is on the with what is on the right hand side. It is a one-direc-

side. In

at

cannot have an expression on the

in a

left

of

mathematical equivalence.

item (5) defines the value of the variable

cy-

be the result of the expression:

radius;

This expression uses three

C

objects in a mathematical expression. All

three objects are user defined: one constant. PI, for the approximation to pi.

and two uses of the floating point variable, radius. The asterisk

(*) is a

sym-

bol for the multiplication operator, so this expression multiplies the values as-

radius, and radius. The result is made the cyl_area. On the next line (item 6). this variable

sociated with the constant PI.

new is

value of the variable

used

in

an expression (again, a multiplication) to calculate the volume of the

cylinder. Both mathematical expressions could easily have been collapsed into a single line. Also,

could have used the

by

obj_volume

=

had we included the standard math function

pow

library,

function instead of explicitly multiplying

we

radius

itself.

height

*

PI

*

pow(radius, 2);

Table 8.3 presents the mathematical operators available evaluation precedence. pressions

in

You can experiment

FirstExpr

.

c

.

in

C

and

their

with them by modifying the ex-

C Types, Operators, and Expressions

8.4

Table 8.3:

Mathematical operators

in

C

Operator

Precedence least

-

Function =>

addition and subtraction

*

=>

multiplication

/

=>

real division if either

+

division

, %

greatest

291

=>

if

operand

real,

is

integer

both operands are integers

integer remainder

Expressions are evaluated in a particular operator order, or precedence.

With respect

to

mathematical operators, division operators are applied

first,

then multiplication, and finally addition and subtraction. In order to modify

programmer must simply enclose the expressions in parentheThe use of parentheses overrides normal precedence. In addition to the standard (canned) mathematical operators, there is a standard math library

this order, the

ses.

(math.h) with the following functions in

Functions

Table 8.4:

in

the math.h function library

Function ceil

it:

Description Returns smallest integer less than x

(x)

cos

(x)

Returns the cosine of x (x

exp

(x)

Returns e to the power x. where e = 2.718

in radians) ..

fabs (x)

Returns the absolute value of x. where x can be real

floor

Returns largest integer not greater than x

(x)

log(x)

Returns the natural logarithm of x

loglO(x)

Returns the base 10 logarithm of x

pow(x, y)

Returns x raised to the power

sin(x)

Returns the sin of x (x

sqrt (x)

Returns the square root of x

tan(x)

Returns the tangent of x (x

Item (5)

in

FirstExpr

the optional field specifier.

.

c

The

in radians)

in radians)

aformof printf which makes use of specifier defines how a variable's value

illustrates

field

y

292

Chapter 8 Introduction to C Programming

will

be printed. In the example, the variable

a floating point variable with the specifier,

where

X

obj_volume

%f format

"6.3" precedes the type specifier. refers to the total

number of spaces

cluding the decimal point, and

decimal point. In

this

Y

is

being printed as

specifier. In addition, the field

The general format

is

'X.Yf,

allocated to print the value, in-

refers to the precision allocated

example, then, six spaces are allocated for

beyond the the number

and decimal point, and three spaces are allocated for precision. Below program compilation and execution. Note the effect of the printfs on the

is

the

print-

ing of floating point variables.

localhost> gcc -o fexpr FirstExpr.c localhost> fexpr **** THIS PROGRAM CALCULATES THE VOLUME OF A CYLINDER **** Please input the following information for the cylinder: radius 3 height 4 You have entered the following: CYLINDER RADIUS: 3.0 00 CYLINDER HEIGHT: 4.000 The volume of the cylinder is: 113.097 :

:

Included below specifiers

is

on different

a brief table of examples which illustrate different field variables,

and what the

on evaluation of the following expressions:

#define PI 3.14159 #define jack "academic" int

x;

double y; x

=

y

=

210; PI + 3;

print f

prints as a result,

based

Table 8.5: 1

293

C Types, Operators, and Expressions

8.4

pr ntf field specifier for fixed and floating point doubles

printf "The sum is @%f@\n", y

=>

The sum is @6.141590@

2

printf "The sum is @%5.0f@\n"

y)

=>

The sum is

@

6@

3

printf "The sum is @%5.2f@\n"

y)

=>

The sum is

@

6.14@

4

printf "The sum is @%5.4f@\n"

y)

=>

The sum is @6.1416@

5

printf "The sum is @%5.5f@\n"

y)

=>

The sum is ©6.14159(3

6

printf "The sum is @%6.4f@\n"

y)

=>

The sum is @6.1416@

7

printf "The sum is @%5.2e@\n"

y)

=>

The sum is @6.14e+00@

8

printf "The sum is @%6.4e@\n"

y)

=>

The sum is @6.1416e+00@

9

printf "The sum is @%e@\n", y

=>

The sum is @6.141590e+00@

10

printf "The sum is @%g@\n", y

=>

The sum is @6.14159@

The

field specifier controls

3, the field specifier is

printed.

played

The

"5

number

first

in, in this

case

5.

.

how

2f " and

specifies

the variable will be displayed. In

controls

how

how many columns

The second number

example

the value of variable "y" the

number

will

is

be dis-

how many significant this case 2. As mentioned

specifies

figures will be displayed after the decimal point, in

what type of format to display the number in, numbers which precede it will be interpreted. The "f specifies display of the number in floating point notation. When the field variable is too small for a number (as in example 1 ), C ignores the field variable and prints whatever number of spaces is required for the entire number. C will give as many significant figures as requested. In example 2. the number is truncated as a result. When a number is truncated, C will round it off to the next significant place, as shown in examples 2, 3, and 4. If the overall number of spaces is insufficient for the number of significant places requested, C will add (pad) the remaining spaces, as in 4 and 5. If the number of spaces requested is

before, the character specifies

and defines

how

the

large, then the variable value

is

right justified

and may

result in leading

blank

Examples 7 and 8 show the same printf field specification as for examples 3 and 6 except that the exponential format (%e) is being used instead of the floating point format (%f ). As before, C will provide enough space to print the number of significant figures requested. Example 9 is a comparison to example Finally, example 10 uses the %g format, which chooses between the %f and %e formats and drops nonsignificant zeros.

characters, as in

examples 2 and

3.

1

.

The same tables can be generated for integers (i.e.. %d) and %s) using the same example variables (and values) above.

strings

(i.e.,

294

Chapter 8 Introduction to C Programming

Table 8.6:

printf field specifier for integers

printf

'x

is @%d@\n",

2

printf

'x

is is @%ld@\n"

,

3

printf

'x

is is @%4d@\n"

,

4

printf

'Jack is @%s@\n"

5

printf

'Jack is @%5s@\n"

,

6

printf

'Jack is @%9s@\n"

,

1

As with

=>

x is @210@

x)

=>

x is @210@

x)

=>

x is

=>

Jack is @academic@

jack)

=>

Jack is @academic@

jack)

=>

Jack is

x)

jack)

real variables, integer

then

number or string.

C

and

@

210@

@

academic®

string variables are printed right justi-

smaller than the integer, or string.

fied. If the field specifier is

entire

and strings

If the field specifier is larger

will right justify the

number

C

will print the

number or

than the

or string with leading blanks.

Type Conversion

8.5 Variable

In C. the variable

on the lefthand side of an assignment must be compatible

with the resulting type of the expression on the will be flagged

(i.e.,

noted) by the compiler

maintained. However, in patible,

when

and no error

will

many

if

some

right. In

cases, an error

assignment compatibility

This

=

not

is

cases the variable types are different but com-

be flagged. The programmer should be aware that

unlike variable types are used together in an assignment statement.

will convert the value of the expression to the type of the variable

y

string.

is

on the

C

left.

called implicit type conversion, or type coercion, as illustrated below.

PI + 3;

In the formatting

while

examples above,

PI was declared

When y

is

a

declared as a real variable (double),

a real constant. In this example. 3

new

being assigned a

hand side of the expression slightly

y was

value,

C

is

an integer

will convert the result

to a real value before assigning

more obvious example which uses characters and

it

literal.

on the

to y.

right-

Consider a

integers.

3;

The character combination

is

"a*

is

converted to

converted to

its

ASCII value before adding

float before assigning the

value to y.

3,

and the

This

is

an

Program Layout and Organization

8.6

example of where

295

up the unwary program-

implicit type conversion can trip

mer, since the addition operation cannot be applied to characters, but the internal representation of characters, in C.

C

also allows the

called a cast.

programmer

as integers.

is

to force a type

conversion using what

is

A cast is an explicit type conversion since the programmer must to make the conversion happen. A cast is invoked by

change program code

wrapping the type declaration

(double)

8.6

3

=>

3

in parentheses, as

shown below.

.

Program Layout and Organization examples above, the following general

In addition to the style presented in

guidelines can be followed to produce programs with

and

readability

few additional motivations programming style.

reusability. In addition to readability, here are a

for paying particularly close attention to •

maximum

Programs

that are difficult to read get

thrown away because they can't be fixed,

improved, or moved to other hardware. •

The simpler

•

Consistency within the program, and with other programmers, requires less read-

the style, the easier the

know where

ing effort, because you •

If

you

rors

8.7 Style for

start

code will be to read.

to look for what.

good

writing the program with

you might get

if

you

tried to put

it

style,

you might avoid generating

er-

in later.

C Program Layout

The program layout should be

similar to the outline of a paper. There should

be vertical separation (with blank lines) between major functional components.

Here are some guidelines for vertical spacing.

•

One blank

line before even, function.

•

One blank

line before

•

Sometimes before and

•

There should usually be one statement or declaration per

Code

is

and

after

after

easier to read

every block or banner comment.

programming constructs such

when

it

is

as loops.

line.

indented with respect to

example, when you type an "if-else" segment, which

is

its

function. For

used to make branch-

ing decisions, then the code associated with the if-else should be indented equally. •

Here are some guidelines on indentation:

Compound

statements should be indented tw

"containing" statement

was indented two

(e.g..

to

four spaces to the right of the

code associate J with the while example, above,

to four spaces horizontal]}

a ith

respect to the line on which the

29b

Chapter 8 Introduction to C Programming

while occurred.

The

•

identifier in declaration lists should be indented the

rounding statements. Variable names should In

•

segment comments are easiest

many programmers Inline

•

comments

to read

when

indent them the

same

are easiest to read

when

Spacing within statements

is

line

up

same amount

as sur-

vertically.

they use the entire line, although

as surrounding code.

they are justified together.

also important for readability.

C does not rec-

ognize multiple spaces, so you could write the following:

a=b+c*e/f +g;

Unfortunately, this

is

really hard

bols, operators, etc. out, the code

on the eyes! By simply spreading sym-

becomes much more

readable.

a=(b+c)*e/(f+g); Of course,

(b+c)

a=

too

much

f+g

e/(

*

space and the program becomes incoherent.

);

Here are some guidelines for horizontal spacing. •

Put one space between identifiers and operators

•

Put punctuation symbols directly after identifiers ter

to distinguish

(e.g.,

p

(a,

c).

b)

;

note space af-

from

(

{

and

}

),

because they are

difficult

plain parentheses.

Organization of

8.7.1

a = b +

comma).

Put space before and after curly braces

•

(e.g.,

C Programs

The organization of a program is as important as any other aspect of its preparation. If you see functions that run on for many screens, then you will understand. Here are some guidelines which will be useful: •

Functions should usually be less than a page or so long.

•

Pass variables needed by functions as arguments; avoid using global variables.

•

Cluster similar items. Put related variables close to each other within a declaration,

One

1.

and put related functions near each other.

last

comment. Every programmer works hard

Functions that perform similai tasks should be organized

in the

same

to

make

place. Also,

their

programs

most programs

have low-level functions on which higher-level tasks are based. Functions of the same abstraction level

should be located

in the

same

place.

8.8 Exercises

29/

and Sample Quiz Questions

run well. However, no one will appreciate a program unless they can understand

how

plicity

8.8

it

and

works.

clarity,

Make

all

of your programs stand out as examples of sim-

and everyone

will enjoy reading

your code.

Exercises and Sample Quiz Questions Exercises

8.8.1

Exercise

1

Change

the

message printed

be free." Recompile and

in

"FirstOut

.

c" to

"Learn C and

run.

Sample Quiz Questions

8.8.2

Problem

1

What

between syntax and grammar

the difference

is

in

C

(any lan-

guage)? Give an example of each.

Problem 2

What

between a low-level programming language

the difference

is

and a high-level programming language. What

is

C? What

are the

strengths of this type of language?

Problem 3

Explain the notion of language portability, and

why ANSI C

is

a

good

dialect to learn.

Problem 4

What

programming

the fuss about

all

is

readability)

.

.

.

what

style

(documentation and

the reasoning behind the use of consistent style

is

conventions? Provide two examples, each, of (1) itemsthat are com-

monly placed

into a program/function banner,

and

(2) readability

guidelines.

Problem

5

There are different semantic blocks of information which comprise a

C Problem 6

program. What are they, and what task does each perform?

What do

the

used, and

Problem

7

Name

symbols

and

{

when should

}

8

Show "

in a

C program? When can they be

a standard function and the library in which

library functions of this kind

Problem

mean

they (according to convention) be used?

a

C

f oo", is

made

it

is

found.

available for use in a

C

How are

program?

expression in which the value of an integer variable,

assigned a value of 65.

following line

is

Show

a

C

named

expression in which the

displayed:

The annual rainfall in Springfield, MA is 65 inches where you can assume teger variable

Problem 9

Why is

it

named

the case that

"

that the value (65) f oo it

is

is

associated with the in-

.

always best

to correct the first error that

find after compiling a program, rather than to fix as

Problem 10

What

is

a function prototype,

and why

is it

many

as

you

you can?

important to use them?

lapte

Decision Making, Iteration, and Functions

Introduction and

9.1

Scope

Although you have learned how have the basic tools

number of values

into the

say to see

fall in

if

they

to write

to construct real

simple programs in C, you do not

programs. For example, you can read a

program, but you do not

a certain range.

and over again, you would have

If

know how

you wanted

to

compare them,

perform a task over

to repeat the expressions as

wanted the task repeated, instead of using a

to

many

iteration construct.

times as you

This chapter

you the elements of programming in C that will provide you with these necessary capabilities, and it will also show you how to write your own functions so that your code need not always be in a single main function. The will teach

Ch9

examples

illustrated in this chapter provide a starting point for using these pro-

gramming constructs, and are available to the student in the "UNIX /Chap ter9" directory for manipulation and modification. The following topics are be presented in this chapter: •

Decision making

•

Iteration

•

Functions and program structure

At the completion of this chapter, you should be able to design and implement simple functional segments which demonstrate flow control and iteration with the different constructs available in the the C programming language. You should be able to write functions, and you should be able to return values from

299

OUO

Chapter 9 Decision Making,

Iteration,

and Functions

you write. You should understand the difference between paramby value and those called by reference, and you should be able to

the functions eters called

use variable addresses to properly assign and return parameter values through function headers. These abilities should be demonstrated in simple programs,

such as those presented

9.2

in this chapter.

Making Decisions In order to

make

a choice between alternatives,

you must have

choose between, you must have some operator which isons,

is

and you must have some metric for evaluating the

ample of two alternatives

is

to execute

one of two

sets

alternatives to

make comparcomparison. One ex-

used

to

of expressions. The as-

sociated comparison might be based on which of two variables has the greater value.

Making

different kinds of

comparisons thus provides a mechanism for

choice.

Simple Comparisons

9.2.1

you have two numbers and you want to know which one is nu(i.e., greater). In C, you use a relational operator for "greater than" between the variables you want to compare. The combination is an exor 1. If the one variable's pression which can be evaluated, and the result is value is greater that the other, a 1 is returned by the operation, otherwise a is returned. Such expressions are called logical expressions, because they return a truth value of the relational operator applied to the operands. It is called a truth value because it can only have a binary value (i.e., zero or nonzero), as do false and not-false. Logical operators and expressions are thus also called boolean operators and expressions. The value of all logical/boolean expresSuppose

that

merically larger

sions

is

either zero or nonzero. Consider the logical expression in

Comparison, variable that

is

c,"

shown

in Fig. 9.1. This

example

"Simple-

illustrates the use

of a

assigned the truth value of a simple logical expression. Vari-

ables which represent boolean variables are often called logical flags, because

they can be used to later decide whether to perform an action.

9.2

Relational operators

Figure 9.1:

in

AUTHOR

*/ */ */

J.B. Hodges August, 1993 Displays the result of a simple comparison between two integers.

/* DATE: /* FUNCTION: /*

301

simpleComparison.c

SimpleComparison.c

/* FILE: /* /*

and comparison

Making Decisions

*/ */ */

*/ Uses stdio.h function library /* Demonstrates the use of > relational op */ */ /* Demonstrates the use of if-else /•••••a**************************************************/

LIBRARIES COMMENTS

/*

ttinclude

int

main (void) {

int x, y,

z

printf "Enter two integers separated by spaces: scanf "%d%d" &x, &y) (

");

(

,

z

©

= x > y;

printf ("The value of return

(

z

is:

%d\n"

,

z);

0)

}

In this simple

and the value of y

example, the value of Z will be is

or 1. If the value of X

2 then the value of the logical expression ,

is

1

.

:

3

2

:

2

3

3

If the vari-

ables or variable values are switched, then the value of the expression

localhost> gcc SimpleComparison.c localhost> a. out Enter two integers separated by spaces The value of z is: 1 localhost>

is

is 0:

!

out Enter two integers separated by spaces The value of z is: a.

This

is

a pretty trivial example;

you can make. The > operator comparisons based on

how

is

however, there are many comparsions

variables relate to each other. Table 9.

er relational operators available in C.

1

that

it makes shows oth-

called a relational operator, because

302

Chapter 9 Decision Making,

Iteration,

and Functions

Table 9.1: Relational operators

in

C

=>

returns

1

if

x

is

less

than y

X

returns

1

if

x

is

less

than or equal to y

X == y

=>

returns

1

if

x

is

equal to y

X

!=

=>

returns

1

if

x

is

not equal to

X

>

=>

returns

1

if

x

is

greater than or equal to

=>

returns

1

if

x

is

greater than

X

y


= y

y y

y

Relational operators always return a value which can be interpreted as true

or false. In addition, any expression

whose value is nonzero can be interpreted whose value is zero can be inter-

as a true logical value, while an expression

preted as a false logical value.

Using Comparisons to

9.2.2 In C,

Choices

comparisons such as that shown above are usually part of a choice be-

example we determined whether x was greater than y. this comparison by asking a "what if* question. For greater than y. then maybe we want to add PI to x. and if it

tween options. In

We

Make

this

can use the result of

example, isn't

if

x

is

maybe we want

9.2). If

we can

the value of 3

to subtract PI

from

express this in C, then

y. as

we can

and y has the value of 5"?

shown

in

"Simple IF

.

ask the question "what

c" (Fig. if

x

has

Making Decisions

9.2

Simple path decisions

Figure 9.2:

/* It********* /*

simpleiF.c

in

***************************************

* *

* * * *

/

*/

FILE:

SimplelF.

AUTHOR

J.B. Hodges August, 1993 Displays the result of a simple comparison between two integers.

*/

/* /*

/* DATE: /

303

*

FUNCTION:

/*

LIBRARIES COMMENTS

*/ */ */ */

*/ Uses stdio.h function library /* Demonstrates the use of > relational op */ /* */ Demonstrates the use of if-else /********************************************************/ /*

:

#include #define PI 3.14159 int

main (void) {

int x,

z;

y,

printf "Enter two integers separated by spaces: scanf "%d%d" &x, &y)

");

(

(

,

z

x

=

> y;

printf ("The value of if

(

z

z

is:

%d\n"

,

z);

printf "Result of choice is: %6.4f\n", x else printf "Result of choice is: %6.4f\n", y return

@

)

(

(

+

PI);

(

-

PI);

0)

}

It

should

come

as

no surprise

that the

of comparison and decision making else)

is

is

C

construct which performs this type

called if-else.

one of the most powerful control structures

guage. The component inside the parentheses

used as a test

compound

in the

if

statement.

The

test is

The

in

if-else (or if-then-

any programming lan-

called a conditional,

and

is

used to decide between two

sets

of

is

expressions. If the test returns a nonzero (true) value, then the

set

of expressions

ed.

Note the format of the

is

selected. if

Otherwise the second else construct

(at

set

item

of expressions

1).

The

if

is

first

select-

and else are

re-

served words, so they must be typed exactly as they appear. The condition

always wrapped are spaced ed, either

in a set

is

of parentheses, and, in this example, the parentheses

from the expression

from a successful

test

for readability. All statements that are execut-

or an unsuccessful

test,

must be terminated.

If

OU4

Chapter 9 Decision Making,

iteration,

and Functions

the statements associated with either the condtional or the alternative

else) form a

When

compound

curly braces are used, the closing curly brace for the conditional expres-

The same

sions should precede the else. the expression

if

(

x

>

y

)

{.

(i.e.,

statement, then they must be enclosed in curly braces.

z

(

)

effect could be

produced by replacing

item (1) with the following:

at

.

way

without changing the

the

program works. The

SimplelF

ed by compiling and executing

localhost> gcc SimplelF. localhost> a. out Enter two integers separated by spaces: The value of z is: 1 Result of choice is: 6.1416 localhost>

3

2

2

3

.

if

construct can be illustrat-

c:

!

out Enter two integers separated by spaces: The value of z is: Result of choice is: -0.1416 a.

An if

important point about the

the condition

control falls

of the is

if

is

if

is

that the expressions

which

are executed

true cannot be reached otherwise. If the condition fails, then

through

can be used

the

if

in C.

to the next executable expression.

The

first is

an

if

without an else.

not met, then control falls through to the end of the

if.

Two other forms

If the

The format

if

is

condition the

same

as before, namely:

if

condition expressions (

{

)

}

The second form allows

for multiple tests,

by immediately following the

else with another if-else statement as follows:

if }

}

}

conditionl { express ions else if condition2 express ions else expressions3 (

)

(

)

{

(T)

9.2

second if-else construct

In this construct, a (1).

The

effect of

condition!

is

this set

of

is

Making Decisions

embedded

tests is to say that if condition

1

in the is

code

305 at

item

not met, and

if

met. then perform the second set of expressions, and so on. This

construct describes an

OR

relation,

meaning

that exactly

one of these

sets

of

expressions will be performed and that they are mutually exclusive.

Any one

of the three forms of

test is

made based on

scribes the range of values

met just

if

(

if

if

can be used to nest

tests.

the success of the previous test.

which meet both

criterion

Nesting means that

Thus

the set that de-

smaller than that which

is

the first test, or the second:

conditionl condition2 if condition3 expressions3 else { } express ions

(T\

)

(

)

(

{

)

}

else { expressionsl }

else { express ions }

This

is

called an

AND

statement, because each successive test

constraining the possibility of inclusion in the final nation of the

ifs

that the actions

No

matter

can be done as well, and of the

first

how complex

these

embedded

gle control structures, so the "outer"

use curly braces.

I

is

two conditionals ifs

if

Also note

is

further

Of course, any combi-

worth experimenting with. Notice are themselves other

if

statements.

statements are, they represent sin-

need not (and,

have used the plural of expression

pressionsl, etc.), so the use of curly braces tional.

set.

is

in general, (i.e.,

mandated

that all the statements associated with

should not)

expressions3, ex-

after the third condi-

an

if

are indented the

same.

Making Choices from More Than Two

9.2.3

The previous decision-making constructs each

Alternatives

select a set of expressions to

The basic mechanism allows a choice between two alternatives. The case where more than two alternatives else constructs, but it is a bit cumberexist can be handled with embedded evaluate based on the result of a comparison

test.

if

some.

C

has an alternative construct, called switch that selects one set of ex-

pressions

among many

possible cases.

The switch

is

a multiple-branch con-

306

Chapter 9 Decision Making,

struct.

in

"SimpleSwitch.

c" below:

simpleSwitch.c */ */

AUTHOR

J.B. Hodges August, 1993

/* DATE: /* FUNCTION:

*/

*/

Displays information about a dog based on family membership. Uses stdio.h function library Demonstrates the use of switch-case-break-default

/*

LIBRARIES COMMENTS

/*

shown

SimpleSwitch.c

/* FILE: /*

/*

is

and Functions

Multiple choice path decisions in

Figure 9.3:

/*

The format

Iteration,

/*

*/ */

*/ */ */

#include int

main (void) {

char dog; 'Enter the type of dog that you own by character \n" Below is a list of options you can use. \n\n" -- G\n" \ \tGolden Retriever -- L\n" \ Retriever \tLabrador -- F\n" \ XtFlatcoat Retriever XtChesapeake Bay Retriever -- B\n" \ -- C\n\n" \ "\tCurlycoat Retriever " Choice: scanf ("%c", &dog)

printf printf printf

.

)

)

-+ switch dog case 'G' case g' printf (" \nGolden retriever: child friendly \n" -« break; case L' case 1 printf (" \nLabrador retriever: dives for rocks. \n" break; case F' case f printf "\nFlatcoat retriever: black-gold. \n" break; case 'B' case 'b' printf (" \nChesapeake bay retriever: bird hungry. \n"); (

)

{

'

.

)

'

'

'

:

)

'

'

'

(

)

break;

® (2)

9.2

Multiple choice path decisions in

Figure 9.3:

case 'C case c printf break; default: printf

Making Decisions

307

simpleSwitch.c (cont)

'

'

'

(

"

("

XnCurlycoat retriever: never seen one.\n");

\nYou need a retriever \n" !

)

}

return

(

0)

}

The switch

invoked as shown

is

variable (in this case

value (2)

is

and

dog)

is

at

item

(1).

The programmer supplied

provided as the condition

The various options "case" is required,

interpreted at run-time. (3).

where the

string

(in

parentheses) and

its

are provided as per items as is the colon after the

choice. In this program, character variables are used in the condition and case;

however, integers can also be used

in the condition.

Both upper and lower case

options were used in this program, to allow for user discretion. Notice that the

empty statement body

after the first case (at item 1).

stacked in this way, the the cases preceding tion

a

it.

first

Once

nonempty statement block a match is found between

When

the cases are

will be applied to all of

the value of the condi-

and one of the options, the corresponding expressions are evaluated

break

is

found. In the switch-case construct, there

is

no need

until

to define a

compound statement and enclose it in curly braces; it is assumed that there will be a number of expressions to evaluate. Unfortunately, the construct doesn't automatically

fall

through to the end of the

ments, and, without a

ments is

in cases

break

which follow,

ended. At that point the

condition and there

is

a

after executing the state-

statement, will continue to execute the state-

until a

switch

break statement is found or the construct is

"default"

exited. If

none of the options match the

expression (item

4),

then the statements

default are executed. Otherwise the switch is SimpleSwitch c in operation is shown below.

following the lustration of

switch

.

exited.

An

il-

OUO

Chapter 9 Decision Making,

Iteration,

and Functions

localhost> gcc SimpleSwitch.c localhost> a. out Enter the type of dog that you own by character. Below is a list of options you can use. -- G Golden Retriever -- L Labrador Retriever -- F Flatcoat Retriever Chesapeake Bay Retriever -- B -- C Curlycoat Retriever Choice: G Golden retriever: child friendly.

Increasing the Specificity of Comparisons

9.2.4

So far, we have talked only about simple comparisons within a condition, those which utilize a single relational operator and two variables. However, it is often the case that you will want to have a condition which makes a more complex comparison, such as to check if values are within a range. For example, you might want to find out if some person's age is between 21 and 30. If so, then you might want to perform some task on the person, and another task if not. In order to determine whether a variable's value is within a range, you have to perform two comparisons. This can be done with nested ifs of course, but that

is

not a single condition. Multiple comparisons in a single condition

require the use of logical connectives. In

programming

logical tests.

it is

For example,

a frequently desirable to if

you want

combine expressions with

to say:

IF xl AND x2 AND x3 OR yl THEN actionsl where "xl," "x2," "x3," and "yl" are potentially complex expressions, then you need to have some mechanism for performing the AND and OR tests. These are called logical connectives or logical operators. The logical connectives in C are demonstrated in the program "CompComp c." .

Making Decisions

9.2

Compound

Figure 9.4:

logical

expression comparisons

in

Compcomp.c

***** /*

*/

CompComp.c

FILE:

/*

*/

J.B. Hodges August, 1993 Performs a compound comparison regarding the use of specialized cloth for sewing.

AUTHOR: /* DATE: /* FUNCTION: /*

/*

*/ */ */ */

*/ Uses stdio.h function library Demonstrates the use of C logical opers */ /* */ for AND (&&) and OR /***************************•****************•***********/

LIBRARIES: /* COMMENTS: /*

(

|

|

#include int

main (void) {

char matl; int hweave,

lweave;

printf "Enter the type of material you are using. \n"); printf "Below is a list of options you can use.\n\n") printf "\tLight Packcloth -- L\n" \ "\tMedium Packcloth -- M\n" \ -- C\n\n" \ "\tCordura (

(

(

"Matl:

")

scanf ("%c", kmatl);

switch case case

case case

(

ma tl

'L' '1'

:

'M'

:

'm'

:

case •C case C '

'

)

{

:

hweave lweave break

=

hweave lweave break;

= 420;

hweave lweave

=

52 0;

=

1000

=

1000 1000

=

=

220; 420;

42 0;

:

:

break;

defau It:

hweave lweave

=

309

O

Chapter 9 Decision Making,

I

Compound

Figure 9.4: if

(

(matl == (matl == (hweave >= (lweave >= (

'L' 1'

)

and Functions

comparisons

logical expression

in

Compcomp

.

c (cont.)

||

)

'

Iteration,

&& &&

)

200) 400)

(T\

{

)

printf \nLight duty: stuff sacks. \n" else if (matl == 'M' (

"

}

(

)

(

)

|

(matl == 'm' && (hweave >= 400) && (lweave >= 400) { printf (" \nmedium duty: back packs. \n" ); else if (matl == 'C (matl == )) ScSc (hweave >= 50 0) && (lweave >= 1000) { printf (" \nheavy duty: mountaineering packs. \n"),else printf (" \nMake jackets with oxford cloth. \n"); )

)

)

}

(

)

(

'

|

|

C

)

}

return

(

)

}

In this example, both the in

compound

OR

tests. In the first

)

( |

and the

AND

(&&) operators are used

|

such

test

(item

1).

the first test

is

to

check the

material type (a char variable). Both upper and lower cases are acceptable an-

swers from the user and so an

OR

relation

ceptable, then the vertical and horizontal

constraining in

tests,

so an

used. If the material type is

is

ac-

checked. These are deemed

AND is used in the expression. The program is shown

execution below.

localhost> gcc CompComp.c localhost> a. out Enter the type of material you are using. Below is a list of options you can use. -- O Oxford Light Packcloth -- L Medium Packcloth -- M -- C Cordura Matl: C heavy duty: mountaineering packs.

is

weave

9.3 Iteration

311

9.3 Iteration Programs are most useful to

in

allowing tasks which are performed repetitively

be codified into a single package. In a similar vein, some tasks are inherently

repetitive,

and programs which solve them are particularly useful. Consider a

simple program which counts from one number to another number in user-provided increments.

None of the programming

constructs which have been pre-

sented so far can perform this task with variable limits or a variable increment.

You would have to print the starting value, add the increment to it, test to see if the new value was greater than the ending value, print the new value, and so on

until

you had written all the statements. If you changed the ending value, would have to rewrite the program by adding or subtracting groups

then you

of statements. Fortunately, task for you: (1)

while,

a looping construct

and

C

(2)

has three iteration constructs which perform this

for, and

(3)

will generally

do-while. Each

be referred

of these

to as such.

We

is

called

will intro-

duce the while construct with the simple counting program called "Count

ByN.c:" 9.3.1

While Loops

A looping construct needs to know:

( 1 )

when

to

perform

iteration,

and

(2)

what

The while loop construct is the most general iteration mechanism in C, because it gives the programmer the most control over when and how iteration is performed. The while loop has two components: (1) a conditional, and to iterate.

(2) a

body, but must explicitly control four related tasks: (1) initialization, (2)

an entry/exit condition, called a loop control expression, which

is

based on a

loop control variable. (3) an update mechanism, and (4) a loop body of associated executable statements.

Ol 2

Chapter 9 Decision Making,

Simple

Figure 9.5:

Iteration,

and Functions

iteration using a while loop in

/* FILE: /*

CountByN.c

/*

J.B. Hodges August, 1993

countByN.c

*/ */

AUTHOR: /* DATE: /* FUNCTION:

*/ */

*/ Displays a table of integers counted */ by an increment between two values. /* APPROACH: Uses stdio.h function library and while */ /* COMMENTS: */ Demonstrates the use of the while loop /* */ Demonstrates the use of two assignment /* */ operators, var++ and +=. /•••••a**************************************************/ /*

#include int

main (void) {

int first,

last,

counter, current;

incr,

printf (" Input the starting/ending integers, and step: scanf "%d%d%d" &first, &last, &incr)

");

(

,

current counter

=

first;

=

1;

-" while current < last printf ("%5d %5d\n", counter, current); counter++; -* current += incr; (

)

{

}

return

(0)

The used

initialization assigns values to the loop control variables

in the

entry condition and the update mechanism. In

initialization

variable,

is

counter

is

noted

at

item

(1).

which are

CountByN.

where current, which

is

c. the

the loop control

assigned

its initial

value. Item (2) also notes an initialization of the

variable,

which

used

times the loop body

is

is

in the

program

to

keep track of how many

executed. Part of the initialization for the while can be

considered the reserved word while

itself,

which invokes

the construct.

The

while reserved word must be followed by the entry condition and the body of the loop.

The loop

control expression defines the loop entry condition and exit con-

313

9.3 Iteration

dition.

The entry condition

is

a test which must be met before the loop body

can be executed. The entry condition

comparison between the value of while entry condition

in the

current

met, the while body

is

example

(at

item 3)

is

condition

satisfied

is

CountByN.

in

the is

tested again.

is

c should be cycled as long as the entry

as long as the value of

(i.e.,

When

executed exactly once. This

called a loop pass or cycle. After the pass, the entry condition

The body of the while

a simple

is

and the value of last.

current

is

smaller than the

value of last).

The update mechanism modifies sion so that

it is

the variables in the loop control expres-

possible to exit the loop. In order to determine whether the loop

can ever be exited, the exit criterion should be looked the negation

(i.e.,

the exit condition

logical is

satisfied

when

equal to the value of last. Since

the value of

last

The while body entry condition

is

as noted at is

the

item

that is

the associated

mechanism must

statement which

CountByN.

compound

while statement and not with respect

is

this

is

example,

greater than or

never changes throughalter

c, the

is

current

up-

when

the

executed

body consists of

current

the decision-making constructs, the while signals a

why

exit condition

(5).

compound

satisfied. In

it

statement, a counter update (item 4), and an update of

As with

The

current

is static (i.e.,

out the program execution), the update

ward toward last,

at.

complement) of the entry condition. In

new

at

a printf

item

(5).

context, and

statments are indented with respect to the to the outer function

(main).

Increment and Decrement Operators The two update expressions in CountByN. c present the application of two new kinds of operators. The first is an increment operator + + ), and the second is an assignment operator + = ). An increment operator performs the same task (

(

as adding

1

to a variable value, except that the

change

in variable

value takes

++ is placed before or after when the + + precedes the vari-

place at a different time depending on whether the the variable identifier. able, as

A

prefix increment

is

shown below.

++counter

In this case, the value of the

evaluated, and then the value of

counter.

If the

++ follows

counter is incremented, the new is assigned. That is, after

expression

is

incrementing

the variable identifier, the operation

is

called a

postfix increment.

counter++ In postfix increment, the expression

is

evaluated, and the value assigned

314

Chapter 9 Decision Making,

to

Iteration,

new, based on

counter.

In both

the

and Functions

present value of

been incremented and has the same value.

ByN.

counter,

examples, after the expression

When

is

before incrementing

evaluated

counter has in Count

used alone, as

two operators have the same effect, but increment operators can be a source of off-by-one errors and care should be taken when using them. There are also decrement operators which function the same way as the increment operators. c, the

Table 9.2: Increment and decrement operators

Expression

Initial

in

C

New

Value

new

=

current ++

=>

current =

1

current =

new

=

++current

=>

current =

1

current

—

=>

current =

2

current =

--current

=>

current =

2

current =

new new

current =

Values 2,

new

=

= 2,

new

= 2

1,

new

=

2

1,

new

=

1

1

Assignment Operators

An assignment operator modifies the basic assignment of variables in an arithmetic way. The assignment operator shown in CountByN c at item (5) is an .

addition operator and works as follows.

The two following expressions below

are equivalent:

current = current current += incr;

+

incr;

Thus, instead of simply incrementing or decrementing the variable

rent,

this operator lets the

programmer

select

what the increment

cur-

will be.

Likewise, there are assignment operators for the other arithmetic operations (Table 9.3).

9.3 Iteration

Table 9.3: Assignment operators

in

315

C

Operator

Example Expression

+=

current += expr

=>

current = current

+

expr

-=

current

-=

expr

=>

current = current

-

expr

*=

current

*=

expr

=>

current = current

*

expr

/=

current

/=

expr

=>

current = current

/

expr

%=

current %= expr

=>

current

of

Equivalent Expression

The use of arithmetic assignment operators c shown below:

CountByN

is

current % expr

illustrated in the execution

.

localhost> gcc CountByN. localhost> a. out Input the starting/ending integers, and step: 1

=

3

31 4

3

2

7

3

11 15 19 23 27

4 5 6

7

where the increment is 4 and the arithmetic operator adds 4 of current during any particular iteration. 9.3.2

The C

to the current value

For Loops for loop performs the

same function

as the while loop;

however, instead

of the abstract structure in the while, the initialization of the loop control variable, the entry condition,

and the updating mechanism for the loop control

vari-

able are defined in the syntax of the construct, so as long as they are defined

properly the loop will exit normally. The format of the for

loop-control-variable-initialization; entry-condition; loop-control-variable-update-expression loop-body

for

}

(

)

{

is

shown below:

316

Chapter 9 Decision Making,

Iteration,

As an example of its

use,

and Functions

CountByN

.

c has been rewritten with a for loop

below. Execution produces identical output.

Simple

Figure 9.6:

iteration using a for loop in

CountByNFor c .

/it*******************************************************/ /* FILE: /*

CountByNFor

/*

J.B. Hodges August, 1993

*/

AUTHOR: DATE: /* FUNCTION: /*

LIBRARIES: COMMENTS:

/*

*/ */

Displays a table of integers counted by an increment between two values. Uses stdio.h function library Demonstrates the use of the for loop

/* /*

*/

.

*/

*/ */

*/

#include int

main (void) {

int

first,

last,

incr,

counter,

current;

printf (" Input the starting and ending integers and the step: &first, klast, &incr) scanf "%d%d%d"

" )

;

(

,

counter

=

1;

Mj

current = first; -«* current < last; -* current += incr { counter, current); printf ("%5d %5d\n" counter++;

for

(

*~

(2)

(3)

)

,

}

return

(

0)

}

In

"CountByNFor

.

c" the for reserved word invokes the construct. The

components of the for control mechanism are all embedded in a set of paOnly the entry condition is a logical expression, the other two can be any legal expression. The initialization expression (at item 1) is an assignment of the value of first to the variable current, which is the loop control variable in this example. The entry condition is the test (item 2) of whether three

rentheses.

current

is

less than the terminating value,

last. The updating expression

(item 3) applies the incrementing assignment operator to

value of but

is

incr. Note

that the variable

otherwise not used

in the

counter

is

used

control of the construct.

able should not be modified in the loop body.

current

in the

The

with the

body of

the for.

loop control vari-

9.3 Iteration

9.3.3

317

Do- While Loops

The do-while loop is identical to the while except that it is used when the loop body should be continually cycled until a condition is met. One of the most frequent uses of a do-while loop is for user input. For example, if the programmer to

a do-while

an appropriate construct to use. Consider the program

is

PosValues Simple

Figure 9.7:

keep typing values

wants the user

.

until a

non-negative value

is

entered, then

"Get-

c" below.

iteration using a

/* FILE: /*

GetPosValues.c

/* AUTHOR: /* DATE:

J.B. Hodges August, 1993

do while loop

in

GetPosValues.c

*/ */ */ */

/* FUNCTION: /*

Reads and displays integers until a non- */ */ negative value is read. /* APPROACH: */ Uses stdio.h function library /* COMMENTS: */ Demonstrates the use of the do-while /********•********•**************************************/

#include int

main (void) {

int readval;

do

{

printf " \nlnput an integer: " scanf("%d", &readval) printf (" \nlnteger value read is: %d\n" readval); while readval gcc GetPosValues.c localhost> a. out Input an integer: -1 Integer value read is: -1 Input an integer: -10 Integer value read is: -10 Input an integer: Integer value read is: Input an integer: 10 Integer value read is: 10 Final integer value read is: 10

Operations with Loops

9.3.4

Many tasks can be performed with loops that will not be presented here but that you should experiment with on your own. A common use is to nest looping you perform the same operations on different variables. For you wanted to produce an addition table, you could run one loop whose control variable is the first addend, and you could run a second loop and whose control variable is the second addend. The operation would only be performed on the inner loop and would perform the addition of the two addends. constructs so that

example,

if

In a nested loop, the inner loop cycles through all of

values for each value

its

of the outer loop, so the inner loop initialization must occur within the outer loop. Nesting can be done with any

Another task cling.

that

the

can be performed with loops

One simple example

a negative integer

is

number of odd

number of variables.

input)

values.

is

count events while cy-

some criterion (say, number of even values and

is

to read in integer values until

is

met. and to count the

The programmer must

create variables to keep the

current tally of even and odd values, and increment

9.4

to

them within

the loop body.

Functions As

a program

debug, and

becomes more complex, it also becomes more difficult to read, The design of a program is usually accomplished using an ap-

test.

proach called iterative refinement.

In this

approach, the original problem

broken into identifiable subtasks. Then each of those subtasks subtasks. and so on until each subtask

is.

finally refined to the point

fined to

its

where

can be written as source code directly. The problem with

is

that

it

none of the code gets written

written,

even though

all

until the

is

is

in turn, re-

most specific code

is

this

approach

designed and

of the higher-level organization has already been done.

Another approach which uses

iterative refinement

is

called

modular pro-

modular programming, the overall problem solution is associated with the main function; however, each subtask can be associated with a

gramming.

In

9.4 Functions

function called by

main. As

the refinement process deepens, the

319

programmer

can define new functions to solve the related subtasks. The functions are themselves miniprograms which address a particular

component of

the overall

problem. The construction of functions and their interaction with the program

which

calls

them

All functions (e.g.. system library functions, user-defined functions, the

main

have the same general structure: a header, declarations, and a

state-

function

)

ment block,

as

shown

Function structure

in

in the function

"MySquare:"

MySquare

/********************************* /*

*******

*/ */

^

MySquare: Calulates the square of a values

*/

/* /* /* /* /* /*

which follow.

Function Format and Definition

9.4.1

Figure 9.8:

will be addressed in the sections

INPUT: OUTPUT: LOCAL: RETURN: USAGE:

varval None sqval double

*/

[main]

*/ MySquare (4) => 16.0 **************************-* /

*/ */ */

double ~* MySquare double varval

function type declaration function header

(

{

double sqval sqval

return

varval

=

(

sqval

)

*

varval; -*

;

function return

Comments The its

function body

first

in

Functions

thing that you should notice about this sample function

own banner comment. The

is

that

it

has

banners associated with a function are different

from those for a program, usually shorter. Functions generally require a banner that tells what the function name is. what it does, what its input and output parameters are, and what

it

returns.

Sometimes, a sample

function banner, to remind the reader of

1.

main is

a function that

ments of a program.

is

the starting point for

all

how

programs.

It

the function

call is useful in the is

invoked.

organizes the source code frag-

320

Chapter 9 Decision Making,

Iteration,

and Functions

Function Parameters The source code shown

in Fig. 9.8 defines a

function called

"MySquare"

which has one parameter "varval," and one local variable, "sqval." A parameter is a variable which is declared in the function header and serves as an interface element to the calling module. Each function parameter must have a one-to-one correspondence with a function argument called.

the value of the local variable If there is

tion

when

A local variable only has meaning in the scope of the another variable with the same it

out adverse consequences. This a variable's value

is

is is,

restricted to the context of the function body.

is

which called MySquare,

the function

function. That

name

in

another function, or the func-

can have a different value assigned to

is

it

with-

called lexical scoping, because the scope of

restricted to the local statements.

Function Types There are two types of functions:

( 1 )

functions intended to return a value; and

(2) functions intended to communicate, and perhaps modify, variable values

MySquare is one of the former which return values can be used on the right-hand side of expressions, since the value they return is typed and should fit into the context of the expression. The library functions sqrt and pow return values and can be used in expressions directly. The value they return takes the place of the function call when the expression in which they reshared with other functions. The function function types;

side

it

returns a value. Functions

evaluated.

is

Function Type Declaration Whether or not a function will.

returns a value,

it

should be declared as though

A void function need not be declared, but good programming

gests that

it is

returned,

it

name

is

best to declare even

void functions. To specify

it

style sug-

the type of value

necessary to specify the function type along with the function

in the declarations.

This

is

done

just prior to the function header.

The

MySquare is declared a double function, meaning that the funcshould return a double value. If a function is not declared, the compiler

function tion

default

9.4.2

is

type int.

Function Application

A function is invoked (i.e., applied) with a function call from another function. The program shown nization and use of

in Fig. 9.9,

MySquare.

"FirstModRet

.

c" demonstrates the orga-

9.4 Functions

Function structure

Figure 9.9:

FirstModRet c .

*************** ************

-*********-

FILE:

FirstModRet

/

AUTHOR

/

DATE:

J.B. Hodges August, 1993

/*

in

321

.

/*

Reads a value to square, squares it, and and then prints both on a line. APPROACH: Uses stdio.h function library. The / /* calculation is performed in function /* MySquare /* FUNCTIONS: MySquare calculates the square COMMENTS Demonstrates modular design for a function with a return value. Demonstrates the use of prototypes. ************************ -**********: ************* FUNCTION:

/ /

:

ttinclude

®

double MySquare (double varval); int

main (void) {

double val,

sq;

printf \nlnput a value to square: scanf("%f", &val); sq = MySquare (val printf (" \nThe square of %6.4f is %6.4f\n\n", val, (

"

"

)

,

)

return

(0)

,-

sq)

322

Chapter 9 Decision Making,

Figure 9.9:

Function structure

Iteration,

in

and Functions

FirstModRet c .

(cont.)

/•••A****************************************************/

MySquare Calulates the square of a values */ */ double varval the value to be squared /* */ double sqval the squared value /* */ None /* */ double sqval */ /* [main] MySquare(4) => 16.0 /******•************************************•************/ /*

/*

NAME: INPUT: LOCAL: OUTPUT: RETURN: USAGE:

:

:

:

©

double MySquare (double varval) {

double sqval; sqval

=

varval

varval;

*

return (sqval);

Program Organization The first thing that you need to notice in this main function is listed first, and MySquare is by the function prototype noted

sible

item

at

listing is the organization.

The

made

pos-

listed second. (1).

A

copy of the function declaration and header (item

The prototype

function body.

is

This

is

function prototype

is

a

4) without the associated

terminated with a semicolon. The prototype

must come before any function definition and there should be one prototype for every function in the

grammer

except for

file,

main. The prototype allows

anywhere

to position functions

in the file,

because

it

the pro-

already has a

definition of the declaration, number, and type of parameters for the function. If the

prototype

is left

out, the

program

will

compile with warnings, since the

may

functions will automatically be declared as type int. which the actual declarations

when

clash with

found.

Variable Type Consistency The second item of

main

interest is the variable declaration in

(item 2).

It is

very important that the variable and function types be consistent throughout the

program and

double,

its

functions.

The parameter varval multiplication, is

returned to

tin.' \

as

The function MySquare

is

declared as a type

double MySquare and,

so the value returned should be consistent with the

ariable

double,

is

is

declared as a

double

in

double variable sqval. The The value returned by MySquare

value of

assigned to a

main

(item 5).

sq (item

2) in the function call (item 3).

so the type logic

is

which

consistent throughout.

is

is

type. after

sqval

assigned to

declared

in

main

323

9.4 Functions

Function Call The

final note

each of

its

of interest

is

the function call

itself.

When

a function

is

defined,

parameters must be declared. They can have any names the pro-

grammer wishes because of variable scoping; however, the order and types must be consistent with the function call, in which function arguments will be paired by order. Because of this requirement, the variable identifiers used in the calling function need not be the

same

There are advantages and disadvantages able identifers the

same between

as those in the function parameter to

doing

functions, the

so. First,

list.

by keeping the vari-

programmer

is

confused with

many

identifiers will

probably make more sense to the programmer

less likely to get

variable identifiers floating about. Second, the variable

with the main, or calling, function.

On

if

kept consistent

the other hand, an important strength

of modular programming and procedural abstraction

is

the separation of func-

tions so that they are't mutually dependent. If the function parameters are as-

sociated with what the function does, and not with what

it is

used for by any

particular function or program, then the function can be used

grams. This extends

its

by many pro-

usefullness.

The function call for MySquare, in main (item 3), has the single argument val. When the function is called, the value associated with val is copied into the MySquare parameter varval. As long as the types are assignment compatible there

is

no problem.

In this case, both

val and varval

are declared

double. localhost> gcc FirstModRet .c localhost> a. out Input a value to square: 5.874 The square of 5.8740 is 34.5039

9.4.3

Functions that Pass Variable Values

As mentioned

previously, there are functions which return values and there are

functions which manipulate variables. There are three kinds of functions that

manipulate variables: (1) output functions, (2) input functions, and (3) input/ output functions.

Output Functions

An output

function

is

one that

may have

values which are passed to

the calling function, but the function itself does not

way which would

affect the calling function.

modify the values

it

from

in

any

The most common form of output

functions are those which print initial instructions to a user or print variable

1.

Strictly speaking,

one thinks of

input, output,

and input/output parameters, rather than functions;

however, there are examples of functions which perform these tasks.

324

Chapter 9 Decision Making,

values, such as

and Functions

Iteration,

"PrintVals"

Figure 9.10: Function structure

in

in Fig. 9.10.

Print vals

/***************************************************•****-/ /*

PrintVals: Prints output variables

*/

/*

/* /*

INPUT:

/* OUTPUT: /* RETURN:

char int None None

first, middle,

*/ */

last

ndogs

*/ */

*/

*/ [main] PrintVals (chl ch2 ch3 num) /••a-*****************************************************/

/* USAGE:

,

void PrintVals (char argl, char arg2

,

char arg3

,

;

,

Mj

int arg4)

,

{

printf

(

"

\nHello, %c %c %c, you own %d dogs, right?\n\n", argl, arg2 arg3 arg4); ,

\

,

return; }

This function has four parameters: argl. arg2. arg3, and arg4. The

char

first

three parameters are

first

function example with

ue. (1).

types, and the last

is

an

int

more than one parameter, and

it

type. This

important to declare each parameter separately. This

It is

Notice that there

turn statement,

PrintVals

and

is

is

our

has no return valis

noted

at

item

only one expression in the function other than the re-

no assignments

that there are

in the function.

function only produces a side effect to display

otherwise has no effect on the program which calls

it.

some

Thus, the

values, but

Besides functions that

return a value, output functions are the easiest to understand, because they effectively take a

copy of the value associated with a variable and perform some

task on

This

is

called call

with a variable

is

provided to the function, the value

it.

by value. Because

a

copy of the value associated in the original

value

is

not

affected.

Input Functions

An

input function

one

is

that has

parameters whose values will be used

in the

calling function, but are initially assigned values in the local function. If

more

module, then the return

state-

than one variable's value

ment cannot be used. case, because

many

is

needed

in the calling

by value would be inefficient

In general, call

variables use a

would be computationally

lot

costly and

memory

such a

would take up even more memory

Since the programmer already knows that the variable value

change, the original

in

of memory. Copying of variable values

is

address and value can be manipulated

going

to

directly

9.4 Functions

This

is

called call

by reference, because

325

the function call uses the address of

The main program can provide to the function the address of the variable whose value is to change, and the function can return a value into that address which main can use. The only the variable rather than the variable value

thing passed to the function

is

the

itself.

memory

address for the variable (see Fig.

9.11):

Figure 9.11: Function parameter passing,

memory addresses, and

pointers

#include #def ine void GetArgs (...); void PrintVals (...) .

.

.

.

int

main (void)

©

{

char fi, mi, int

la;

nd;

GetArgs (&fi, &mi return

,

&la,

1234567

&nd)

B

(0)

-^

7654321

H

memory void GetArgs (char *fip, char *mip, char *lap,

inst *ndp)

{

scanf "%c%c%c" fip, mip, scanf "%d" ndp) (

,

lap);

(

,

The main function and

the function

it

calls

can share the same address and

values, but have different identifiers. In Fig. 9.1 is

used

In the

GetArgs

char" variables.

A

pointer

address.

1.

item 1) to reference the addresses of the

(at

is

A

the address-of operator (&)

char

variables

mi and

la.

function header, parameters are declared of type 'address-to-

These are called pointers, because they "point"

to the variable.

an object that can be referenced like a variable, but represents an

pointer

is

declared as follows.

326

Chapter 9 Decision Making,

type

*

Iteration,

and Functions

identif ierp

Example

Type

Pointer Identifier

char *fip

=>

char

int *ndp

=>

int

fi P

*

ndp

*

type * declares a variable to be a pointer of type type, and identif ierp is the identifier for the pointer. Using this notation, f ip mip, and lap are pointers to char variables, and ndp is a pointer to an int variable. where

,

The "p" pointer. ers.

in the identifier It is

name

not required, but

The pointer

is

to a variable

helps to remind the

is

programmer

that this is a

for keeping track of point-

and the address of a variable are different ways

of referencing the same variable (item the address (at item 3)

mechanism

a useful

2).

The

(variable) value associated with

then the same even though

it

being referenced

is

through different identifers. Fig. 9.12

the

shows an example of

keyboard

in the

Figure 9.12: Output parameters

in

function

a typical input function that reads values

GetArgs

and returns them

to

from

main.

GetArgs

/••••••••••A*********************************************/ /*

GetArgs:

*/

Reads input variables

*/

/*

*/ None */ char *firstp, *middlep, *lastp */ /* int *ndogsp */ /* LOCAL: None */ /* RETURN: None /* USAGE: */ [main] GetArgs (&fi, &mi, &li, &nd) /•a******************************************************/ /*

INPUT: /* OUTPUT:

;

void GetArgs (char *firstp, char *middlep, char *lastp, int *ndogsp)

©

{

printf "\nPlease type your initials, separated by no spaces: scanf "%c%c%c" firstp, middlep, lastp) printf (" \nPlease type how many dogs you own: "); scanf ("%d", ndogsp) (

(

,

return;

")

9.4 Functions

The function parameters: item 1) are the addresses in

f

irstp, middlep, lastp, and ndogsp

memory

stored. Notice at item (2) that

memory

O.c,"

is

9.13. This

the

two functions

.

are repeated for coherence.

top of the

file,

because

functions in any order. This program

dRet

.

c.

main

is

C

just presented. In this

Note

that the

similar to the previous

main

program,

function

is

allows the programmer to organize

similar in organization to

Item (1) notes the function prototypes for

Vals. Also

PrintVals and "FirstModl-

program does the same thing as the display and input segments of the code

c program; however, the implemented with the functions we have at the

al-

complete program,

are

organized

because the parameters

functions, particularly

illustrated in the following

illustrated in Fig.

FirstIO

is

addresses.

The use of input and output

GetArgs

(at

where the variable values are the variables being read with scant do not re(pointers)

quire ampersands (address-of operators). This

ready represent

327

program

is

GetArgs

FirstMoPrint-

and

the use of local variables in

(item 2), which hold the values that are associated with the functions.

328

Chapter 9 Decision Making,

Iteration,

Figure 9.13: Use of input parameters

in

and Functions

FirstModio.c

/******************************************************-**/ /*

FirstModlO.C

FILE:

*/

/*

*/

/*

AUTHOR: /* DATE: /* FUNCTION:

J.B. Hodges August, 1993

*/

*/

Reads user's initials and number of dogs */ and then prints them on one line. */ /* APPROACH: Uses stdio.h function library. Input is */ /* */ separate from main. Output is separate /* */ from main. /* FUNCTIONS: */ GetArgs reads the input data /* */ PrintVals: displays the output /* COMMENTS: Demonstrates modular design for I/O with */ /* */ functions. /••it*****************************************************/ /*

:

#include

void PrintVals (char argl char arg2 char arg3 int arg4) void GetArgs (char *firstp, char *middlep, char *lastp, int *ndogsp) ,

,

,

Mj

;

int

main (void) {

char fi, mi, int

la;

(2)

nd;

GetArgs (&fi, &mi &la, &nd) PrintVals fi, mi, la, nd)

(3)

,

(

return

(

;

0)

}

Referring back to Fig. trates the use

9. 12, the

function call for

GetArgs

(item 3) illus-

of call by reference, since the address-of operator refers to the ad-

dress of the associated variable.

So any

which

variable

is

manipulated

in a

function will be referenced in the function call with an address-of operator (just as for

scant and

GetArgs

for the

same

reasons). This

is

why On

are passed in with address-of operators.

the four arguments to the other hand, an out-

put function does not need to have consistent values for variables with ing function, so a

copy of

its

call-

the variable value can be sent into the function. Al-

though our examples have used

all call

by reference or

call

by value,

this is not

What is important is that the programmer recognize which arsomehow coming back into the main or calling function and

a requirement.

guments arc which are not.

9.4 Functions

Figure 9.13: Use of input parameters

in

FirstModio.c

329

(cont.)

/*********************•**********************************/ /*

*/

GetArg: Reads input variabless

*/

/* /* /* /*

/* /*

*/

None

INPUT: OUTPUT: LOCAL: RETURN: USAGE:

firstp, middlep,

ndogsp

lastp,

*/ */

None None

*/

GetArgs (&f i

[main]

&mi

,

,

&li,

*/

&nd)

void GetArgs (char *firstp, char *middlep, char *lastp,

Mj

int *ndogsp)

printf \nPlease type your initials, separated by no spaces: scanf "%c%c%c" firstp, middlep, lastp); printf (" \nPlease type how many dogs you own: scanf "%d" ndogsp) (

"

");

(

,

"

)

(

,

return; }

/***********•********************************************/ /*

PrintVals: Prints output variables

*/

/*

*/

/*

INPUT: /* OUTPUT: /* RETURN: /* USAGE:

first, middle,

ndogs

last,

*/

None None

*/ */

PrintVals (chl

[main]

void PrintVals (char argl

char arg2

,

,

,

ch2

,

ch3

char arg3

num)

;

*/

int arg4

,

{

printf

("

\nHello, %c %c %c, you own %d dogs, argl arg2 arg3 arg4 ,

,

,

right?\n\n",

\

)

return; }

The program FirstModIO c .

is

compiled and run below.

localhost> gcc -o fmioc FirstModIO. localhost> fmioc Please type your initials, separated by no spaces: JBH Please type how many dogs you own: 2 Hello, JBH, you own 2 dogs, right?

O\30

Chapter 9 Decision Making,

Iteration,

and Functions

Modular Programming and Procedural Abstraction

9.4.4

The design of programs using functions utilizes the method of iterative refinement discussed on page 319. The idea of looking at a problem statement and identifying the different tasks which need to be performed is the basis for all program development. The modular approach to program development uses programming constructs with predictable behavior to design the program. Procedural abstraction means that the conceptual subtasks which are used to solve a problem, or a subproblem,

make up what

for the problem. If these subtasks can be

solution to a subtask interface

is

called an abstraction level

is

implemented with functions, then the

kept distinct from the problem

itself,

because only the

shared between the original function call and the function imple-

is

mentation. If each conceptual level

grammer is

is

implemented

in this

way, then the pro-

change how a task is implemented, or solved, without components of the problem. Procedural abstraction has some of which are discussed in Chapter

free to (later)

affecting the other

many

benefits,

1

In order to illustrate the application of

dural abstraction, let's construct a

program

1

modular programming and proce-

to solve the simple but possibly real

problem presented below:

Box

Balls in a Suppose

that

you have

store in boxes,

box

and

that

as possible. Write a

a

number of

you want

you want

balls that

to store as

many

program which, given

to

balls per

the diameter

of the balls and the dimensions of the box will return the

number of

balls that will

This

into the box.

fit

that all balls for a particular

box

is fairly

You

will be the

illustrative

can assume same diameter.

of the types of programming problems that you

are likely to see, except that normally the

an example of how the input played.

now,

We

is

to

problem statement

be formatted and

will consider this aspect of the

as long as

it

looks reasonable

when we

how

will also include

the output

problem somewhat

is

to

be dis-

arbitrary for

are done.

Solution Feasibility

The question

that

one must ask oneself before embarking on

even be done? This that

it

is

this task

called a question of feasibility. Clearly,

could be done, as long as

we can

figure out the

it

volume of

is:

can

it

makes sense the

box and

volume for each ball, because we can then divide one by the other to get the number of balls. Almost. Balls will actually take up more volume than their own volume, so we have to have the actual volume that the ball requires. Now. can we do this? The answer is yes! The next step is to identify the mechanism the

whereby

the

problem solution

will be

brought about.

We

have written our po-

9.4 Functions

tential

approach

in English, but

formalized description of identify the

how we can puts. In this

gorithm

volume volume actual number number number number

is

how

we need

to translate this into

to solve the

331

an algorithm, a

problem. In order to do

so,

we must

knowledge domain needed to solve the problem, and then show use it to get from the program inputs to the desired program outexample, the domain knowledge is algebraic, so designing the al-

not really a problem:

= length x width x height of box of ball = 4/3 x pi x radius-cubed volume of ball = (2 x radius) -cubed of actual volumes along length = length / (2 x radius) = width of actual volumes along width / (2 x radius) of actual volumes along height = height / (2 x radius) of actual volumes that will fit into box nicely = 0\ j x (2j x (3)

As you can problem, but

it

see, is

we do

not really need the volumes for the balls to solve the

better to write

down

extra information and

wonder why you cannot solve description already needs some refinement in how we name cide on a few variable names now: clusion than to leave

boxvol ballvol actvol numvlength numvwidth numvheight numvols numballvols numacts

=

it

out and

come

to this

con-

the problem. This things, so lets de-

blength x bwidth x bheight x PI x ballrad x ballrad x ballrad 8 x ballrad x ballrad x ballrad blength / (2 x ballrad) bwidth / (2 x ballrad) bheight / (2 x ballrad) numvlength x numvwidth x numvheight boxvol / ballvol boxvol / actvol

= 4/3 -

= = = =

= =

As you can

see,

we have

kept the ball volume and actual volume for com-

parison purposes, and that there are really only 4 input variables

bwidth, bheight. brad) and one cess. All the other variable values

(blength,

constant (PI) that are used in this pro-

can be calculated from these.

Subtask Refinement

Now

that

we have some

to solve the Balls tasks.

Here

defined).

is

a

faith in the eventual success of

and Boxes problem, we need

first

developing a program

to organize the

program by sub-

cut at an algorithm (the algebraic tasks have already been

Oo2.

Chapter 9 Decision Making,

and Functions

Iteration,

display instructions

obtain values for 4 variables

perform volume calculations for box and

ball

perform comparison calculations display information

modular programming approach, each of these subtasks will either in the main function or they will be handled by functions. Since we have already seen two functions in this chapter that perform similar tasks In the

be statement

as items labeled (1), (2)

and

our needs accordingly. This

assume that we can modify them to suit where modular programming satisfies the need

(3), lets is

for code reusability.

Framework Construction Often the most

difficult task in writing a

main

program

is

to write that first level of

committment to the variable names, their types, and the function types, even if you think they might change later on. Lets give it a try. Lets modify the program FirstModlO. c, because it has a similar structure. Here is what I have done prior to displaying the program below: functions and the

Copy

rename

the file and

Edit the banner

Add known Modify

to protocols, calls,

we

and headers.

already have to do the right thing.

Leave stubs for the functions we haven't written

Granted

in

this is a

The 9.14. The

yet.

number of steps, but we do not want to print file, named "BallsAndBoxes

intermediate

times.

Fig.

requires a

main program and the functions.

for the

names

the functions that

many

It

it.

comments

variable

program.

.

three functions that

were similar

to

this thing out

c,"

shown

is

PrintVals

and

GetArgs

should be very straighforward to understand, as the the same func-

tionality

invoked from them and only the names and number of variables,

and

literal strings,

math add

is

are being changed. Item (1) notes that

library functions if

this

we

are going to use the

include statement, the program will

plain during execution, but

you

will get

still

pow

we have

function. If

compile, and

it

to

add the

you do not

will not

com-

junk for the values associated with the

was never used. Item (2) notes that we have to add a constant for PI for the true ball volume calculation. Item (3), notes the function protocols for the program. This is really a very good way to keep track of all the variables you have chosen, especially if you have the main program located at the function which

top of the

file,

since your function calls will

all

be close to the protocol defini-

333

9.4 Functions

tions ing.

and

it

will be easier for

you

programmer of what these odd I

perform type and argument position check-

to

Item (4) notes that sometimes some inline comments serve to remind the identifiers refer to.

never place variable descriptions

tion banner.

I

have placed them inline

space. Item (5) tells the novice

For

my own

inline, but, rather, in the in this

C programmer

example

programming. program or func-

for conservation of

that functions without argu-

ments must use parentheses or the function will not be invoked. You get an error, but nothing related to the function will happen. Item (6)

bly the one interesting thing in this

first series

of changes.

variables, such as

blen

are being passed in but are not

function, whereas others, such as

boxvolp

proba-

We have not mixed

input and output variables in previous examples; however, in

some

will not

is

CalcVols

changed by the

are being modified in the func-

Hence you see both call by value and call by reference in the function and you will also see it in the protocols (item 3) and headers (item 7).

tion.

call,

334

Chapter 9 Decision Making,

Iteration,

and Functions

Figure 9.14: Main program and function calls for /* ********** /* FILE: /* /* AUTHOR /* DATE: /* FUNCTION: /* /* /* APPROACH /* /* /* FUNCTIONS /* /* /* /* COMMENTS

BallsAndBoxes.c * *

BallsAndBoxes

/

*/ */ */ */ */ */ */ */ */ */ */ */ */ */ */

.

J.B. Hodges August, 1993 Reads information about boxes and balls and returns information about how many balls will fit into the box. Uses stdio.h function library. Uses the algorithms for box volume and sphere volume GetDims reads the object dimensions PrintNums: displays the number of balls CalcVols: calculates object volume CompVols: compares object volumes Demonstrates modular program design 'A-****************************; ************•*•**•***••**• * * :

i

#include #include #define PI 3.14159

void PrintDirs (void) void GetDims (double *blenp, double *bwidp, double *bdepp, double *bradp) int *numvlengthp, int *numvwidthp, int *numvheightp) void CalcVols (double blen, double bwid, double bdep, double brad, double *boxvolp, double *ballvolp, double *actvolp, void CompVols (double boxvol, double ballvol, double actvol, int *numvolsp, int *numballvolsp, int *numactsp, int numvlength, int numvwidth, int numvheight); void PrintNums (int nact, int nballs, int nvols);

© ® ®

int

main (void) double blength, bwidth, bheight, ballrad, boxvol, ballvol, actvol; int numvols, numballvols, numacts, numvlength, numvwidth, numvheight; PrintDirs GetDims (kblength, CalcVols (blength, &actvol, CompVols (boxvol (

)

*/ box dimensions */ ball dimensions /* volume variables */ /* output variables */ /* /*

©

;

&bwidth, &bheight, &ballrad) bwidth, bheight, ballrad, kboxvol, &ballvol, &numvlength, &numvwidth, &numvheight ballvol, actvol, &numvols, &numballvols, fcnumacts, numvlength, numvwidth, numvheight); PrintNums (numvols, numballvols, numacts); return (0) ,

)

©

9.4 Functions

Figure 9.14:

PrintDirs function

for

BallsAndBoxes.c (cont.)

/****************************************-* user

***********************

/* PrintDirs: Prints instructions to /* /* INPUT: None /* OUTPUT: None /* RETURN: None /* USAGE: [main] PrintDirs (

/

)

******************************************************************

void PrintDirs (void) {

printf

\n

************************************ • * * *

* * *

BALLS AND BOXES

* * * * * * * * *

** * * * *

* * *

*** * * *

* * * * * * * * * * * * * * * * * * * * *

* ** ****

return;

:

-q

ir

\

***\n" \ ***\n" \ This program calculates the number ***\n" \ of balls of radius 'R' that will ***\n" \ fit into a box of dimensions 'L', ***\n" \ 'W and 'H' ***\n" \ ***\n" \ The user enters the box dimensions ***\n" \ and the ball radius. ***\n" \ ***\n" \ The program displays the number of ***\n" \ balls that will fit based on three ***\n" \ measures ***\n" \ ***\n" \ ***\n" \ (1) cubic volume displaced ***\n" \ (2) true volume displaced ***\n" \ (3) actual volume displaced ***\n" \ *********************************** ******* \n\n-) ,

* * *

\

.

335

336

Chapter 9 Decision Making,

Figure 9.14:

Iteration,

and Functions

GetDims function and function stub

for

calcvols function

(cont.)

/•••it**************************************************************/ Reads box and ball dimensions variables */

/* GetDims: /* /* INPUT: /* OUTPUT: /* RETURN: /* USAGE: /* /* /*

*/ */ */ */ */ */ */ */

None blenp, bwidp, bdepp, bradp

None [main]

GetDims (fcblength, &bwidth, kbheight, &ballrad)

/••••••••••••••••A*************************************************/ void GetDims (double *blenp, double *bwidp, double *bdepp, double *bradp) {

printf \nPlease type the box dimensions, separated by spaces: scanf "%f %f %f blenp, bwidp, bdepp); printf (" \nPlease type the ball radius: "); scanf ("%f", bradp); (

"

" )

(

"

,

return; }

/* CalcVols: Calculates object volume /* /* INPUT: blength, bwid, bdep, brad /* OUTPUT: boxvolp, ballvolp, actvolp, numvlengthp, /* numvwidthp, numvheightp /* RETURN: None /* USAGE: [main] /* /* CalcVols (blength, bwidth, bheight, ballrad, &boxvol, &ballvol, /* &actvol, &numvlength, knumvwidth, &numvheight /* )

*/ */ */ */ */ */ */ */ */ */ */

/******************************************************************/ void CalcVols (double blen, double bwid, double bdep, double brad, double *boxvolp, double *ballvolp, double *actvolp, int *numvlengthp, int *numvwidthp, int *numvheightp) {

return; }

®

9.4 Functions

Figure 9.14:

/* /* /* /* /* /* /* /* /* /*

CompVols function stub and PrintNums function

(cont.)

*/ */ */ */ */ */ */ */ */

CompVols: Compares object volumes INPUT:

OUTPUT: RETURN: USAGE:

337

boxvol, ballvol, actvol, numvlength, mimvwidth, numvheight numvolsp, numballvolsp, numactsp None [main]

CompVols (boxvol, ballvol, actvol, &numvols, knumballvols, toumacts, numvlength, numvwidth, numvheight);

*/ */

/*

void CompVols (double boxvol, double ballvol, double actvol, int *numvolsp, int *numballvolsp, int *numactsp, int numvlength, int numvwidth, int numvheight) {

return; }

/* PrintNums: Prints output variables /* /* INPUT: numvols, numballvols, numacts /* OUTPUT: None /* RETURN: None /* USAGE: numballvols, [main] PrintNums (numvols

*/ */ */ */ */ */

numacts); /******•*********•***************•****************************•*•**/ ,

void PrintNums int numvols, int numballvols, (

int numacts)

{

printf ("\nCUBIC DISPLACEMENT: %3d balls will fit into the box\n" "TRUE DISPLACEMENT: %3d balls will fit into the box\n" "ACTUAL DISPLACEMENT: %3d balls will fit into the box\n\n" numvols, numballvols, numacts);

\ \ ,

\

return; }

What we have

in this first

attempt

not function properly simply because

is

a

program which

some of the

will

compile but will

guts are missing. Let us

now

complete the phase with one of the functions, and leave the other as an exercise.

We decided earlier that the calculations that we we could

wanted

to perform,

that calculate the object volumes and the number of along any particular box dimension, would be as follows.

ball

given

volumes

338

Chapter 9 Decision Making,

numvols numballvols numacts

= = =

Iteration,

and Functions

numvlength x numvwidth x numvheight boxvol / ballvol boxvol / actvol

so

all

we need

to

do

is

convert this pseudocode

into the function statement block. This has

Figure 9.14: Pseudocode conversion

in

1

into source

code and

dump

it

been done below:

compvols (cont

.

/* CompVols: Compares object volumes /* /* INPUT: boxvol, ballvol, actvol, numvlength, /* numvwidth, numvheight /* OUTPUT: numvolsp, numballvolsp, numactsp /* RETURN: None /* USAGE: [main] /* /* CompVols (boxvol, ballvol, actvol, &numvols,

*/ */ */ */ */ */ */ */ */

/*

*/

&numballvols, &numacts, numvlength, numvwidth, numvheight);

/*

*/

/•••••••••A********************************************************/ void CompVols (double boxvol, double ballvol, double actvol, int *numvolsp, int *numballvolsp, int *numactsp, int numvlength, int numvwidth, int numvheight)

M)

{

*numvolsp *numballvolsp *numactsp

=

= =

numvlength * numvwidth boxvol / ballvol; boxvol / actvol;

*

numvheight;

return; }

Notice that those variables which are being called by reference use what

is

called the indirection operator, and those that are called by value are used directly.

The

indirection operator takes as an argument a pointer and returns the

associated variable. Hence,

if

we want

only have access to through a pointer, tion operator.

As

.

we must

dereference

a final illustration of functions in C,

run from the program

I

to assign a value to a variable

we just

I

am

it

which we

with the indirec-

including a sample

developed.

Pseudocode means an English version of the algorithm that is so close to source code that it is It is often easier to write source code on paper as pseudocode and translate it when

one step away. editing.

9.5 Exercises

and Sample Quiz Questions

339

localhost> gcc BallsAndBoxes.c localhost> a. out ******************************************* ***

***

BALLS AND BOXES

* * *

* **

*** This program calculates the number *** of balls of radius 'R' that will *** fit into a box of dimensions 'L', *** 'W and 'H'

***

The user enters the box dimensions and the ball radius.

* * *

*** ***

,

** *

The program displays the number of *** balls that will fit based on three *** measures: ***

* **

*** *** ***

(1) (2)

(3)

* **

cubic volume displaced true volume displaced actual volume displaced

*** *** ***

***

******************************************* Please type the box dimensions, separated by spaces: 12.5 24.1 10.5 Please type the ball radius: 2.25

CUBIC DISPLACEMENT: TRUE DISPLACEMENT: ACTUAL DISPLACEMENT:

9.5

20 balls will fit into the box 66 balls will fit into the box 34 balls will fit into the box

Exercises and Sample Quiz Questions 9.5.1

Exercises

Exercise

1

Complete the

program Exercise 2

last

make

to

after the

it.

BallsAndBoxes and run the works properly with your function.

function in

sure

Write a program that

5000

Exercise 3

to

it

starts

entire

with the integer 1000 and repeatedly adds

After each addition, print the resulting sum.

What happens

sum exceeds 2.147.483.649°

Write a program that accepts as input an integer "n" and then adds "1

0/n" to itself "n" times. For example, if the input is 5, then the sum is the real number "1.0/5 + 1.0/5 + 1.0/5 + 1.0/5 + 1.0/ 5." After computing this sum. the program should compare it 1.0" and "not to 1.0 and output the word "equal" if the "sum = equal" otherwise. Run your program with different values of "n" and try to determine the smallest integer for which the sum does not equal 1

.

.

.0.

This type of error

is

called a round-off error.

340

Chapter 9 Decision Making,

9.5.2

Problem

Iteration,

and Functions

Sample Quiz Questions 1

Which

relational operator(s) can be used to identify if data

C

read into a

named

a variable

Write a

C

the value

value.

When

that

its

that the data

is

value should be from

which

is

assigned to to 9. inclu-

test.

that reads values into an integer variable "foo."

name of the

within range, print the

the value

variable.

variable and

its

out of range, print an error message and the

is

The range

is

shown below:

logical connective operators (&&

!

,

,

combinations of logical expressions.

|

=) are used to construct

Provide an expression which

performs the same function as the one provided

Problem Problem 4

is

< foo < 9

•

The

Assuming

correct?

and

"foo,"

program

When

name of the

Problem 3

is

provide a set of expressions that perform the

sive,

Problem 2

program

in the latter part

of

1.

Rewrite the program

in

"bar" and compound

Problem 2

to use

logical expressions.

two variables: "foo" and Use the ranges of values

below. 10

Problem 5

< foo < 99

< bar < 9

•

What

are the

components

to a general iteration construct?

ponent does an entry/exit condition

fit

and what

into,

is

What com-

the relation-

ship between an entry condition and an exit condition?

Problem 6

Write a

C

program

to read in 10

numbers from the keyboard and

to

count the number of values which are less than 25.

Problem 7

Which

arithmetic operator can be used to determine even multiples of

number? Which assignment operator can be used decrement a number? a

Problem

8

Wrote

a

C program

to read in 10

numbers from the keyboard and

count the number which are multiples of to a

Problem 9

power equal

What

is

to the

to exponentially

3.

Print the

number

to

3 raised

number found.

the importance of the function call/function header relation-

ship?

Problem 10

Write a

C

program which

their values,

and prints the

with a function.

iteratively reads

result.

10 values, accumulates

Implement each functional segment

10.1

Introduction and In this chapter,

we

Scope

will extend

your

arrays and structures. In Chapter 9.

C programming

include the use of

skills to

you extended your

ability to write

simple

programs, enabling you to direct execution, repeat code segments, and develop

your

own

functions. In order to take full advantage of the

power of these con-

you must be able to use them to locate and compare data as well as to use the data generated. Simple variables can be used as long as they are being used right away, but otherwise a structured variable, one that keeps track of many variables and their values, is needed. Once the need structs, particularly iteration,

for variable organization

nization in data files, so

is

recognized, a logical extension

you

will then learn

how

is

to read data

to use the orga-

from a

file into a

and write it out to a file from a structure. Finally, often the data you compare requires access to different variable types, in which case new structured data types are necessary. We will introduce these concepts and their application in small examples, the source code for which can be found in the "UNIX/ChlO" directories. The following topics wil be addressed in this chapstructure

want ChlO

1^

to

ter:

Comparing

results of

Reading data from a Writing data out

many

iterations

file into

an array variable

to a file

Structured variables for unlike data types

More on memory addresses

When you

have completed

this chapter,

you should understand how array

341

342

Chapter 10 Arrays, Structures, and Files

and structure data types are defined, declared, accessed, and used in simple programs and functions. You should be able to read values into array and structure types, and you should be able to read information from text files into program variables or write information from program variables to text files.

10.2

Comparing One

Iterations Using Arrays

of the most useful functions of iteration

which

are indexed to a loop counter.

feature because that they

we

did not have any

So

is

to

compare values of variables

we have

far,

not been able to use this

way of organizing

variables in such a

could be indexed (related) to one another and.

so,

compared by

way their

order.

10.2.1

The Array

An array

is

as Structured Variable

a structured variable in that

same type. An array scheme for accessing identifier

char double

and a type

is

organizes

it

the values of those variables.

like

many

variables of the

actually a collection of variables, and an indexing

An

array variable has an

any other variable, as shown below:

obj_type; obj_sizes [20] In this

example.

variable because

it

obj_type

j_sizes

is

variables

organizes, and

it

is

a regular variable, often called a scalar

can only have one value

an array variable. its

Its

identifier

double

type

On the other hand, obobj_sizes refers to all of the

at a

is

time.

the type of

all

of the variables

it

An array is declared when the identifier is associated with more than value by square brackets and a value. obj_sizes actually declares double variables, since its type is double and the value in brackets

organizes. a single

up is

to 2

2 0. Although the value

is

2 0. the value

is

only used to define the largest

number of variables which can be associated with 10.2.2 Using

Array Variables

A programmer can do with array lar variables.

the array variable.

variables anything that can be done with sca-

They can be accessed, assigned

values, reassigned values, and

they can be used as arguments in functions. Moreover, the array index (the

number inside the brackets, e.g., 20 in [20]) can also be manipulated in the same ways. The array index always starts at and goes to n - 1, and the index must always be an integer or a character. Let's look gram,

"SimpleArr

.

c" (Fig. 10.1

)

at

an example pro-

and see how arrays work

in

C.

10.2

Figure 10.1: Array Usage

Comparing

Iterations

343

simpleArr.c

in

*/

;:~;leA:r.:

/* FILE:

Using Arrays

/*

*/

/*

AUTHOR

/* DATE: /* FUNCTION /*

/* /* APPROACH -it**********/

J.B. Hodges August, 1993

*/

Calculates an addition table of integers and then determines how many of them are multiples of a user input value. Uses stdio.h function library. Uses array

*/ */

*/

*/ */

#include #define MXSZ1 100 #define MXSZ2 200 int

main (void) {

f starting addend values

startl, start2, maxl max2 add[MXSZl] [MXSZ1] counterl, counter2

int

,

f /'

incr,

/

vals[MXSZ2], numincr;

/'

*/ */

limits of each addend storage array loop counters the search increment values matching search the number of incr found

*/ */ */ */ */

printf "Input starting and ending integers for addendl scanf "%d%d" &startl, &maxl) printf "Input starting and ending integers for addend2 scanf "%d%d" &start2, &max2 printf "Input the search increment: " scanf ("%d", &incr) (

")

(

,

(

")

(

,

)

(

)

numincr

=

0;

for counter2 = start2 counter2 gcc -o CmdArgSum CmdArgSum. localhost> CmdArgSum 3 4

The

3

in the

and 4 here are called

command

main block of CmdArgSum.c

arguments. To do

line

this

we

include

the following:

void main(int argc, char *argv[])

The operating system knows that are included

on the

(as strings) to the array etc.

Note

that

argv

is

to assign to

command

argv

line,

and

as elements

argc

the

to assign

argv

[

]

number of arguments

each of these arguments ,

argv

[

1

]

,

argv

2

[

an array of unspecified length, where each element

is

]

a

pointer to a string. In the example:

localhost> CmdArgSum

3

4

5

argc gets the value 3, meaning that there argv is always the command name, [

is

]

the string

"CmdArgSum."

Table 10.1:

are 4 arguments.

All of the values are

argv values

in

command Value

Element

argv[0]

=>

"CmdArgSum"

argv[l]

=>

"3"

argv [2]

=>

argv [3]

=>

"

4

"

"5"

The

first

so the value assigned to

line

shown

in

argument

argv

Table 10.1.

arguments

[

]

Array Variables

10.3

in File

Operations

34 1

10.3 Array Variables in File Operations Our

last

program had a special nested loop

how

used to show

and

to generate

have

arrays are used.

we can

which we

written a single nested loop

but that would have been less fun and wouldn't

test the values,

set us up for this example.

would be nice

It

from a

table into an array variable

to generate the values

We could have

read large data

UNIX

file

if

we could

read the addition

and then analyze

it.

If

we can do

arrays and perform bulk anal-

this,

then

ysis.

We can let someone else worry about how to generate the data file.

ing data from a

file into a local

subtasks: (1) declaration of a

when

Read-

data structure requires the completion of three variable, (2)

file

finished. (3) close the local

There are two types of nary

files into local

file.

files that

These

open the

file for

reading, and.

will be the topics of this section.

can be read

in C:

(

1

)

text files,

and

(2) bi-

Most files which are read into programs are text files, and most of you have seen in this book are text files. A text file is an ASCII, or

files.

the files editable,

file.

In a text file,

each viewable

The end of

nevvline character.

line

ends with a special character

The end-of-line character

called an end-of-line character.

is

which cannot be seen under normal All of the information in the

file:

characters at the end of each

line,

as a

editing. After the last end-of-line character

the characters for ever)' line, the end-of-line

and the end-of-file character, are organized

as a single set. or string, of characters.

When

the file

is

viewed, the end-of-line

characters are interpreted, and you "see" lines on a screen.

The

which makes up the

is

file is

associated with a name, which

set

of characters

the filename.

referenced in the operating system just as a variable

is

known

another special character, called an end-of-file (EOF) character.

in the file is

filename

also

line character is usually a control character

is in

The

a program.

10.3.1 File Declaration

To

read from a

be declared

file

in the

(instead of the keyboard or standard input), a variable

program which

tem. This will be called a

we

file

must

will represent the file in the operating sys-

variable. Since the local variable and the real

file

them by making use of the file's address in memory. Thus the file available in the program must be declared as a pointer associated with the file which can be referenced in the program. Until now. we have referred to pointers as the memory addresses of variables, and that is what they are. but it is easier to call them pointers, so we will do so henceforth. The file are different,

variable

FILE *infilep,

is

refer to

declared as follows:

*outfilep;

where inf ile might represent the name of a file that data will be read from. and out file might represent the name of a file that data will be written to. There need not be any correlation between the file name and the pointer vari-

348

Chapter 10 Arrays, Structures, and Files

able,

have done

I

to identify pointers

pointers and

10.3.2

A

is

an example only. The notation of using a "p" after a ptr, or some other notational mechanism) makes it easier in source code. The "FILE *" type is associated with file

this as

pointer variable (or

required.

Opening a Local

file is

opened

File for

for use with the

Read or Write

fopen

function,

ments: (1) a string that represents the local

and

file

(2) a character that designates whether the

fopen requires two argu-

name

in the operating system,

file is to

be used for reading

The return value of a call to fopen is a pointer to the file, and it is the pointer which is used in subsequent operations (i.e., read and write). Consider the program "SimpleFilelO. c" shown in Fig. 10.2, which illustrates the use of files for reading values into arrays and writing them back to files when done. The first portion of the figure is documentation the ("r") or writing ("w").

way

I

like to prepare

Figure 10.2: Array Usage

in

it,

as

opposed

to other

examples

in this text.

simpleFileio.c

/************* ****** ******************************************** /* FILE: /* /*

AUTHOR

/*

DATE: FUNCTION:

/* /* /*

/*

APPROACH LIBRARIES:

Hodges August, 1993 Reads values from the UNIX file system a local array select values within a user defined range, and writes those to another file in the UNIX file system. Uses arrays to store the file contents. Uses the string function library.

*/

*/

J.B.

*/ */ */ */ */ */ */

/* /*

*/

CONSTANTS

/*

STRSZ 20 100 MAX

-

Maximum string size Number of allowable successes

*/ */

*/

/* /* /* /* /*

/* /* /*

/* /*

/* /* /*

/

*/

,

/* /*

* *

Simpl eFilelO.C

VARIABLES

FILE FILE char char int int int int int int int int

*infilep *outfilep infilen [STRSZ] outfilen [STRSZ] val lower upper vals[MAX] succ[MAX] counter, counterl nsucc status

-

*/

input file pointer output file pointer input filename output filename value from infilen limits of age range limits of age range storage array ages in range loop counters number of successes number args fscanf read

*/ */ */ */ */ */

*/ */ */ */ */ */

/* /* ****** ****** ******

********************************************

k

*

/

10.3

Figure 10.2: Array Usage

Array Variables

simpleFileio.c

in

in File

Operations

349

(cont.)

#include #include #define STRSZ 20 #define MAX 100 int

main (int argc, char *argv

[

]

{

*infilep, *outfilep; infilen[STRSZ]

FILE char

,

outfilen [STRSZ] int

val, lower,

upper, vals [MAX] succ[MAX] counter, counterl, nsucc, status;

strcpy (inf ilen, argv[l]); strcpy (outfilen, argv[2]); infilep = f open (inf ilen, "r"); outfilep = fopen (outfilen, "w"

printf "Input the youngest/oldest ages in search range: scanf "%d%d" &lower, &upper) (

(

,

counter nsucc

= =

;

;

status = f scanf (inf ilep, "%d", &val); status == 1 && counter < MAX; status = f scanf (inf ilep, "%d", &val) vals [counter++] = val;

for

for if

(

)

counterl = 0; counterl = lower && vals [counterl]

Use CFILE

as the core

-e PFILE

=>

Use PFILE

as the executable file

-s SFILE

=>

Read

the

symbol

table

from

SFILE

-se PFILE

=>

Read

the

symbol

table

from

PFILE

-q

=>

Don't print introductory banners (quiet option)

-x CMDFILE

=>

Execute

dump

gdb commands

to

from

examine

and use

it

as the executable file

CMDFILE

Once started, gdb takes and evaluates one command at a time. The commands can be of any length, and their names can be abbreviated up to the point where they cease

to

are three types of

commands

serve.

be unambiguous. Other than exiting the debugger, there

The step, next,

in a

debugger: (1) execute, (2) stop, and (3) ob-

run, and continue

commands

are execute

commands.



Exits

blank line

=>

Repeat the

help [name]

=>

Show

gdb last

command

gdb command name, gdb

information about

information about using

break FUN

=>

Set a breakpoint at the entry to function

break LIN

=>

Set a breakpoint at line

break FIL:FUN

=>

Set a breakpoint

break *address

=>

Set a breakpoint at

enable BNUM

=>

Enable the breakpoint(s) specified by

disable BNUM

=>

Disable the breakpoint! s) specified by

clear FUN

=>

Remove any

condition BNUM EXPR

=>

at

FUN

number LIN

FUN in

function

address

FIL

file

(asterisk

breakpoints for function

Break for break number ates

or general

BNUM when

is

required)

BNUM BNUM FUN

expression

EXPR evalu-

nonzero

backtrace FRM

=>

Show

frame FRM

=>

Examine

up N

=>

Select and print the frame

down N

=>

Select and print the frame

stack frames for frames the stack for frame

FRM

FRM

N frames up from N

frames

the current frame

down from

the current

frame

info frame

=>

Displays information about the current

list LIN

=>

Displays ten lines centered around line number

list

=>

Displays ten more lines

list-

=>

Displays ten lines before the lines

print expr

=>

Display the value of an expression

step

=>

Execute each statement one

run [arglist]

=>

Start

c

=>

Continue running your program

your program, with

at

last

frame

LIN

printed

a time

arglist.

if

specified

after a breakpoint

11.4

11.4.2

gdb - A Sample

Using

Debuggers

383

Session

A sample run using a debugger can quickly show the merit of using gdb during program development and testing. Consider the bus error that was discussed in section 1 1 .2.2. The error was in the scant function, where the programmer had forgotten to use an ampersand (&) to reference the input variable. To use gdb with this program, the following sequence could be followed:

localhost> gcc -g CountByN.c localhost> gdb -q (gdb) add-file a. out (1j) Reading symbols from /Users/hodges/a. out .. .done done Reading symbols from /usr/shlib/libsys_s B. shlib. (gdb) run (g) Starting program: /Users/hodges/a out Input the starting/ending integers, and the step: 1 100 10 (3) Program generated(l) Memory access exception on address 0x50242fc (protection failure) 0x501564e in _sys_nerr () (gdb) bt (4) .done. Reading in symbols for countbyn. c #0 0x501564e in _sys_nerr () #1 0x64 in ?? () x501514e in _sys_nerr () #2 #3 x504d5b2 in _sys_nerr #4 K3e3 6 in main () at countbynbug c 22 (gdb) list 22 17 main (void) .

.

.

.

:

.

.

(

.

18

19 20 21 22 23 24 25 26

:

{

int

first,

last,

incr,

current;

counter,

printf (" Input the starting/ending integers, scanf "%d%d%d" &first, &last, incr); (

,

v current counter

=

first;

=

l,

ns

Error Here continued..

In this

ByN

.

sample session, an error was introduced into the program "Count

c" in the scant

call,

by removing the required ampersand address-of op-

incr

The program was comfile for debugging. The '-q.' debugger was then started with the quiet option, The first command issued by the user from within gdb, (item 1), was to load the executable file "a out" into the debugger. The response from the debugger is to display the path to the executable and some other information. The next command (item 2) was to run the program. Although this sample session will only show the ac-

erator

from the variable

piled with the '-g' option,

.

(see 'Error Here' line).

which

sets

up the executable

384

Chapter 11 Programming Tools

commands and responses from a debugging session, the user can issue commands for assistance at any (gdb) prompt. Simply type "help" to get a list of top-level topics, or "help topic" to get a list of lower-level topics for a specific top-level topic. You can then see what alternatives and optual

tions there are.

The

program (a out)

which where the values 1,100, and 10 were input to correspond to the variables "first," "last," and "incr." The debugger then notes a memory address exception and provides the address where the error occured. At this point, it is often useful to find out result of running the

.

displayed by the program. This

is

where at

4).

noted

at

item

is

This provides a

full listing

the request for input

(3),

execution trace the error occured, so

in the

item

is

I

type "bt" (for backtrace,

of the trace by stack frames, which are

basically function call environments, along with associated address entry is the address in main and the line on which the error was program had had many functions, instead of just one, then the backtrace would have shown the function calling sequence all the way back to main. The frames lower than scant in the backtrace are calls from scant, so

points.

Most

useful

flagged. If the

the actual error

was detected

inside of scant.

The

line

number next

to

main

helps to locate which scant produced the error.

Item (5) notes a

now know

ther side of line

22

to

(gdb) list *0x3e36 0x3e36 is in main (countbyn. c 22 17 main (void) :

18 19

command

to

list

to look there for a problem.

show

the source code at line 22, because

The debugger

will then

list

lines

on

context.

(6) )

{

first,

int

20 21 22 23 24

last,

incr,

counter,

current;

printf "Input the starting integer/ending scanf "%d%d%d" &first, &last, incr); (

...

(

,

current counter

25

=

first;

=

1;

26

gdb c ont i nue (jj Continuing. Program generated (1) Memory access exception on address 0x50242 fc (protection failure) 0x501564e in _sys_nerr () (gdb) step (8) Current function has no line number information. Single stepping until function exit. (

)

:

1

1

Program exited normally. (gdb) quit

^^^

____

(9)

we ei-

Another

command, by address, and the address, not just

listing

type the asterisk

385

Developing Program Libraries

11.5

shown

is

at

item

the address.

(6).

Note

The user must

that the listing

is

identical.

From

this point

and

tify the error,

it

becomes necessary

this is not

programmer be able

that the

to iden-

always easily done, and requires more familiarity

with the debugger. This session

is

only intended to provide the novice with

enough clout

to use the

the available

commands. The command

debugger and

to

experiment further on your at

item (7)

tells

own

debugger

the

with

to re-

sume execution of

the program, after which the execution is stepped (item 8) which happens to be a single step. Normally, stepping allows the user to 'walk' through program execution and view the environment, but in this case the error occurred right away so stepping was of little value. Item until termination,

(9)

shows

the exit

Program Libraries

11.5 Developing

Header

11.5.1

Large

C

from the debugger.

Files

programs are often divided

into several

bined with the use of #include statements.

We

components which

are

com-

have used #include statments

to library functions. The #include statement inheader file, which is a listing of the function prototypes for the function names, and corresponds to a C source file by the same root " (i.e., it has a c" suffix) name. Programmers can define their own libraries by creating the appropriate header and C files, and then including them in whatever programs require the library.

to provide access in a

cludes what

program

called a

is

.

When created:

creating a library of functions from a source

( 1 )

two new

file

with the

files are

name of the library followed by h" and (2) name of the library followed by " c." The header "

a header file with the

a source code file

file,

.

.

consists of the constant definitions and prototypes for each function in the

library,

and should have a general banner describing the

library: its use,

its

con-

tents,

and any suitable comments. The declaration for each function prototype

in the

header

file

should be preceded by "extern," which declares the proto-

type to be exportable to other

files.

The primary requirement of using user-defined clude statement, double quotes

( "

" )

er file instead of the normal angle braces (
).

"My_Functions

brary into a program would appear as

libraries is that, in the in-

are used to delimit the

.

name of the head-

Consider the inclusion of a

c."

shown below.

The

inclusion of this

li-

oOD

Chapter 11 Programming Tools

Figure 11 .5:

A header file

template

/*******•**********************•************************/ /*

My_Functions

.h -

header file

*/

/* /*

*/

Library of functions intended to support some task

*/

Included functions:

*/ */

/* /* /*

funcl func2

/*

...

*/

/* /*

funcn

*/

*/

*/

#define XYZ

(J)

/***************************************•***************/ /*

funcl banner from source code file

*/

extern typel funcl (parameters)

/******************************************•*•**********/ /*

func2 banner from source code file

extern type2 func2

*/

(parameters);

The creation of the source code library "My_Functions c" may require some changes to the source code for the functions. The functions should be rewritten to make them as general as possible. This may include changing constant and function names, and possibly moving constants into the function parameter list. In addition, the header file must be included, as shown above, for .

both the program which uses the library and the library implementation (i.e.,

types must be

Figure

1 1 .6:

Use

My_Functions c Of course, removed from My_Functions c first.

source code

file),

of a user-defined

.

.

file

the function proto-

.

header

file in

the implementation

file.

#include "My_Functions h" .

/********************************************************/ */ Complete definitions of the functions listed in */ My_Functions .h /••••a**************************************************/

/* /*

When file

the header file

and source

file

are created for the library, the source

needs to be compiled so that you have an object code

file

for

it.

This

is

done

Organizing and Maintaining Complex Programs

11.6

by using the -c' compiler option on the library source code *

file,

as

OOi

shown

be-

low:

localhost> gcc -c My_Functions

.c

After this step

is

complete, you can use the function library by loading the

object file for the library (and including the header

source

file

of course)

when you compile

file in

the

new program

a program which uses the

library:

localhost> gcc -o My_Prog My_Functions.o My_Prog.c

11.6 Organizing

and Maintaining Complex

Programs The student has been introduced to basic programming and programming skills with the C programming language. These skills will only be useful as a stepping stone to improving your skills, and will only provide you with enough knowledge to read and experiment further on your own. The programs you have seen and written in this part of the text are single file programs, meaning that all of the source

code resides

libraries are included in that file.

system and user-defined

in

one

file in

the operating system,

and

all

Most application programs make use of many

libraries,

source

files,

and object

files.

When develop-

ing large programs, you will frequently find yourself needing to edit one seg-

ment of

the overall program. There

and link

all

is no need for you to manually recompile which depend of the programs on the modified module(s). A utility

make

allows you to define, beforehand, how all of the components of program fit together, and will then determine, when make is invoked, which files have to be recompiled and compile them. This way the programmer

called the

is

freed from having to think carefully about what program segments must be

makes certain that the recompilation is done correctly. This you to make and show you how to create a simple makefile. After that you should look in the reference section for more information on make, what it can do for you (which goes beyond compilation and recompiled, and

it

section will introduce

simple tasks), and 11.6.1

how

to use

The Makefile

make organizes the tasks gram.

it.

Some

that

need

to

be performed to maintain a complex pro-

tasks involve changes to source code and recompilation. Others

involve installing

new

executables in the proper directories. Others involve

building archives or installing the program from archives. construction and installation of online

man pages

Still

others require

for the application,

make

388

Chapter

11

Programming Tools

takes as an argument a

what actions need

to

called a makefile,

file,

"Makefile" or "makefile."

A

which

is

typically

named

makefile identifies each organizational task by

be performed, and by the dependencies between actions

and the components of the program.

A dependency describes executable program has

When you modify

the source

recompile the source

a relationship

at least

file

file, in

that object file is

file

file,

files.

and

order to get the

and produce a new object

cutable depends on the object file. If

between

one source

and the object

one object

file.

new

executable you must

file.

We

file

needed by another program

For example, every

at least

say that the exe-

depends on the source

in order to

compile, then

you can begin to see that the executable file may depend on many source files and object files whose dependencies are sequentially and hierarchically defined. When you create a makefile, you define the dependencies for the different components of your program and its associated organizational tasks. When you want to perform any of these tasks, you simply invoke the makefile with an argument which is associated with the task you want performed. This procedure is illustrated below for six different organizational tasks. % % % % % %

make make make make make make

program clean man install archive

In this example, the

project and,

if

make

utility will,

by

default, use the makefile for the

given an argument, such as 'program,' 'clean,' 'man,' 'in-

stall,' or 'archive,' the associated actions.

will search for that task in the makefile

When

no argument

is

provided,

make

and perform

generally de-

faults to the first task in the makefile.

11.6.2 Constructing a Makefile

Consider the construction of a simple makefile tasks

to

perform the organizational

mentioned above for a simple program. The makefile has three

section types, as illustrated below: •

Macros

•

Dependencies

•

Actions

distinct

11.6

Figure 11.7:

A template

Organizing and Maintaining Complex Programs

makefile

=

compiler_version program_executable_name primary_source_code list_of_objectf ile_dependencies list_of_libraries_used list_of_compiler_options location_to_put_executable location_to_put_manpage

=

${ PROG}. tar

CC

=

PROG SRC OBJS LIBS CFLAGS BINDIR MANLIB ARCHIVE

=

= = =

= =

Oo9

# PROGRAM program: ${OBJS} ${LIBS} ${CC} -o ${PROG} ${CFLAGS} ${OBJS} ${LIBS} ${SRC}

#OBJECTS objects: ${LIBS} ${CC} -c ${LIBS} #CLEAN clean:

/bin/rm -f core ${OBJS} #MAN man: cp ${PROG}

1

$

{MANLIB}

# INSTALL

${OBJS} ${LIBS} /bin/uncompress $ {ARCHIVE} tar xvf $ {ARCHIVE} ${CC} -o ${PROG} ${CFLAGS} ${OBJS} ${LIBS} ${SRC} mv ${PROG} $ {BINDIR} cp -r ${LIB} ${MANLIB} cp ${PR0G}.1 $ {MANLIB}

install:

|

# ARCHIVE archive /bin/tar cvf

$

{ARCHIVE}

The

/bin/compress

$

lines labeled item (1) are called

for the makefile.

©

{ARCHIVE}

macros, and represent

Macros can be referenced anywhere

in the

local variables

makefile by pre-

ceding them with a dollar sign ($), as with shell variables, and embedding the macro name in either a set of curly braces ( { } )or a set of parentheses ( ). (

The use of macros makes

the makefile easier to read

example, macros have been defined as noted as necessary

at

(item

and reduces typing. In 1),

by the appropriate items when referenced

expression or an action expression. Item (2)

is

a

)

this

and would be replaced in either a

comment, which

dependency

is

ignored by

o90

Chapter 11 Programming Tools

make, and follows (#)

is

used

it

then nothing after

Item (3) identifier,

is

on the

delimits the target from is

on the

make

has three components: (1) a target

dependencies, and (3) a

The

on the dependencies. The target to

It

of the colon, (2) a colon, which separates/

left side

its

sign line,

by make.

relation.

right side of the colon.

argument

If a

will be interpreted

it

dependency

a

is

which

comments. Anytime a pound pound sign is seen anywhere on a

the convention of shell

denotes a comment.

means

relation

identifier is

list

of dependencies, which

dependent what the programmer uses as an that the target is

during invocation.

Items (4 to 10) define the actions taken for various tasks associated with various targets.

Any

The

action

must begin with

use of tabs after column

but the tab in action.

As

column

a

column 1. by make,

character in

are ignored (except for readability)

make

used by

is

1

a result, any

1

to

determine that what follows

number of lines can follow

the

dependency

an

is

relation

and

be counted as associated actions as long as they begin with a tab character. Item (4) is the action to

cies

perform when code

between the various objects and

is

modified, and defines the dependen-

recompile

libraries that are necessary to

the program. In this example, only the template has

been shown; however,

in

real example, each object file would have its own dependency relation. Some tasks do not have source/binary code dependencies, such as the "clean" task, c 1 ean removes any core files which are leftover from code de-

any

velopment, and

is

simply a

UNIX

script.

Item (5) defines the dependencies and action necessary to compile the braries to produce the object files

need for program compilation. Item

action associated with placing the

quires that the

macro

manpage

MANLIB

for

which the

library

(item 6), the source code

is

is

and

re-

be defined.

Items (7 to 10) are the actions to perform stallation, in

the

(6)

in the appropriate location,

li-

is

all

the tasks associated with in-

unarchived using

uncompress

compiled as before, the executable

is

tar

and

placed

in the

appropriate directory (item 7), the appropriate libraries are placed in the correct directory (item 8), and the

man page

is

moved

(item

9).

Item (11) defines actions to perform to archive the

program. The archival requires a name of the directory

gram

files

can be found, and then the directory

is

files

in

associated with the

which

all

of the pro-

archived using

tar and

compress. Let us

now

for the Balls

compiling that ments. •

consider a more realistic example, by converting the program

and Boxes problem so library,

that

it

has a source code library, separately

and writing a makefile

The following items describe Create the header

file for

to organize the

the procedure

the Balls

we

will use.

and Boxes functions

program seg-

•

Create the function library for the Balls and Boxes program

•

Modify

•

Create the makefile

•

Test the makefile

the original

BallsAndBoxes.c source code file

for the

functions except main into

anew

associated header

be called

file will

A sample header file

BandBF

for

'library.

.

file

program

Recalling the Balls and Boxes problem,

Figure 11.8:

391

Organizing and Maintaining Complex Programs

11.6

1 '

we

will begin

We will call

"BandBF

.

it

by moving

"BandBF

.

all

c".

h":

c

/+********•****************************•***************************/ ^*************** Balls and Boxes Function Library *****************/ *****************/ /*************** /it************************* header file ***************************/ /*****************************************************•***•********/

*/ PrintDirs Prints instructions to user /**************+***********************************************•***/

/*

:

extern void PrintDirs (void) /*

GetDims

:

Mj

;

Reads box and ball dimensions variables

*/

extern void GetDims (double *blenp, double *bwidp, double *bdepp, double *bradp)

/************•************•****•*******************************••**/ */ Calculates object volume /********************•*************************•****•**************/

/* CalcVols:

extern void CalcVols (double blen, double bwid, double bdep, double brad, double *boxvolp, double *ballvolp, double *actvolp, int *numvlengthp, int *numvwidthp, int *numvheightp)

/*******************•******•***************************************/ */ CompVols: Compares object volumes /••it***************************************************************/

/*

extern void CompVols (double boxvol double ballvol, double actvol, int *numvolsp, int *numballvolsp int *numactsp, int numvlength, int numvwidth, int numvheight) ,

/

/*

PrintNums: Prints output variables

*/

extern void PrintNums (int numvols, int numballvols,

1.

This

is

not actually a library, since

we

will

move

all

the functions for the

Normally, a library would consist of those functions which have a tions

which operate on a

common

data type.

int numacts)

common

program

into this

file.

function, or the func-

the

The

392

Chapter 11 Programming Tools

Each of the function prototypes as noted at item (1), so that

it

is

declared as

will be available

The associated BandBF c implementation .

Figure

1 1 .9:

Implementation

file

BandBF c .

for

'extern'

in the

header

file,

by functions defined elsewhere.

file is partially

shown

new BallsAndBoxes

.

in Fig.

1 1

.9.

c.

/A*****************************************************************/ /*************** Balls and Boxes Function Library *****************/ /*************** *****************/ /*********************** source code file *************************/ /****************•****************************•********************/ #include #include #include "BandBF. h"

Mj

#define PI 3.14159 /*

*/

Normal Function Definitions Here

Note ies

that the

header

used by the functions

any constants (item 2) is

file is

included

at

in this library.

that are

item

It is

(1),

along with the other

librar-

also important to locally define

used by the functions

in the library.

often unnecessary to include/define these items in the

As

such,

it

main program seg-

ment. In this example, PI has been defined for the use of the functions for the Balls and Boxes problem, but these functions comprise the entire procedural component of the program (outside of main), so this may not be indicative of all

programs.

Next we ticular case,

In general,

will

modify the original Balls and Boxes source file. In this paronly included in the program the main function segment.

we have

however; we might have many segments with many functions

in

each. In this particular example, once the function prototypes are replaced by the inclusion of the header

file, little is left in

main

(as

shown

in Fig. 11.10).

Organizing and Maintaining Complex Programs

11.6

393

Figure 11.10: Main program modifications for Ball sAndBoxes.c :*****•******:

/*- ***********

BallsAndBoxes

/* FILE: /* /* AUTHOR /* DATE: /* FUNCTION: /* /* /* APPROACH /* /* /* FUNCTIONS /* /* /* /* COMMENTS /

*/ */ */ */ */ */ */ */ */ */ */ */ */ */ */

.

J.B. Hodges August, 1993 Reads information about boxes and balls and returns information about how many balls will fit into the box. Uses stdio.h function library. Uses the algorithms for box volume and sphere volume. GetDims reads the object dimensions PrintNums displays the number of balls CalcVols: calculates object volume CompVols: compares object volumes :

:

Demonstrates modular program design

it**************- ******: ********************:

************* ******/

#include #include # include "BandBF.h"

®

#define PI 3.14159 int

main (void) {

double blength, bwidth, bheight, ballrad, boxvol, ballvol, actvol; int numvols, numballvols, numacts, numvlength, numvwidth, numvheight;

PrintDirs GetDims (&blength, &bwidth, &bheight, iballrad) CalcVols (blength, bwidth, bheight, ballrad, &boxvol, &ballvol, &actvol, &numvlength, &numvwidth, &numvheight CompVols (boxvol ballvol, actvol, inumvols, knumballvols, toumacts, numvlength, numvwidth, numvheight); PrintNums (numvols, numballvols, numacts); (

)

)

,

return

(0)

The

final task is to create the

makefile. In this case,

use the names of the

gram

is

complete,

we

files

we

will

macros which

name

we have

will call

it

the makefile

will be

used

in the

sample

"Makefile," and we

generated for this example.

When

will

the pro-

"BAB," for Balls and Boxes (item

1

in

The only personal library used in this example is the "BandBF. c" source code file, so it will become the single component of the $ {LIBS } mac-

Fig.

1

1.10).

394

Chapter 11 Programming Tools

ro (item 2). Likewise, the result of compiling

"BandBF.o," which

is

We will also include the main The Figure 11.11:

result is

Makefile for

= BAB PROG = BandBF.o OBJS = BallsAndBoxes SRC = BandBF. LIBS = cc CC CFLAGS = BINDIR = -/bin MANLIB = -/lib ARCHIVE = ${PROG}.tar

"BandBF

.

c"

is

the object file

component in the ${objs} macro. function file in this component (also at item 2).

the only object

shown below:

new BallsAndBoxes

.

c

program (T\

^

(2)

.c

# PROGRAM program: ${0BJS} ${LIBS} ${CC} -c ${LIBS} ${CC} -o ${PROG} $ {CFLAGS} ${OBJS} ${SRC}

#

rest of makefile is the same as the template

Note modified

that the original template, for this particular at all!

this particular

First

we

The

definition of the

program.

example, has not been

macros takes care of the idiosyncrasies of

Now let's test the file to see if

will recompile an executable as

shown

at

it

lives

up

to

its

promise.

item (1) below. In this case,

Mj

localhost> make cc -o BAB BandBF.o BallsAndBoxes localhost> Is *.o

.

BandBF localhost> make clean /bin/rm -f core *.o localhost> !ls .

Is

*

.

[2j

o

No match.

localhost> make cc -c BandBF cc -c BandBF cc -o BAB BandBF.o BallsAndBoxes .

.

.

localhost> make archive /usr/ucb/compress BAB. tar /bin/tar cvf BAB. tar humpback [127] Is BAB*

(Aj

|

BAB*

BAB. tar.

we

already had a copy of

"BandBF

.

o" from a previous

tost,

so only the over-

Recommended Reading

11.7

all

compilation was performed. As proof that

sary components, the (at

we

'clean' option

then remove the object

that

we implemented

will recompile the neces-

file for the

item

(at

2).

function library using

Then we re-make

the file

item 3) and note that both passes (the library compilation and the final com-

pilation) are performed. Finally (item 4),

which tars and compresses

11.7

make

395

we

the source

execute the

code

'archive'

option,

tree for the project.

Recommended Reading Learning

to

Program

in

C

Kernighan, B. and Ritchie, K. [1991]. The tice Hall,

Hanly,

J.

Englewood

and Koffman,

E.

Program Design Oram, A. and

Cliffs,

C Programming

Language, Pren-

NJ.

and Friedman, F. [1993]. Problem Solving and

in C,

Addison Wesley, Reading,

MA.

Talbott, S. [1991]. Practical C, O'Reilly Associates, Seba-

stapol,

CA.

C Programming and UNIX Advanced C Programming Kernighan, B. and Pike, R. [1984]. The Prentice Hall,

Rochkind, Marc

J.

glewood

Englewood

[1985]. Cliffs,

UNIX Programming

Environment,

Cliffs, NJ.

Advanced UNIX Programming,

Prentice Hall, En-

NJ.

Make Oram, A. and

Managing CA.

Talbott, S. [1991].

sociates, Sebastapol,

Projects with Make, O'Reilly As-

This final part of the text combines the concepts and

utilities in

UNIX with those

in the

C

program-

ming language. A programming language can be extremely useful for manipulating UNIX files, commands, arguments, and responses. Each command shell has its own programming language. and a program written for a particular shell is generally called a shell script. Unlike an executable C program, an executable shell script is not a binary file. The shell command interpreter reads each line of the program and evaluates it. This part of the course introduces you to the tools you will need for shell programming in the C Shell and the Bourne Shell. You are not expected to become fluent in writing shell scripts, nor are you expected to become a good programmer by writing a few simple scripts. However, you are expected to learn how to write a shell program in each environment, which includes the use of general programming functionality applied to UNIX system commands and responses. No aspect of either command shell's programming language is presented in much detail. Generally, a topic is introduced that covers a broad range of programming situations. An example is discussed that illustrates how that topic fits into the UNIX programming environment and how it is used. By the end of each chapter, you should have a few template examples that enable you to construct simple working scripts that exhibit behavior commensurate with the topics leading up

to

and including those introduced

in the chapter.

Regular Expressions

and Scripts

12.1

Introduction and A

shell script

evaluated in a

is

Scope

an executable

UNIX command

comprised of expressions which can be

file

shell

by the

language used to control the evaluation of

programming language. Much

shell

matching

a desired pattern with a

UNIX

UNIX

.

or

utility,

The matching process

command on is

Regular expressions

•

egrep

•

avvk

•

sed

language

is

the

have completed

regular,

are helpful in

the patterns

which succeed the match.

means

for comparing, or

matching patterns.

topics will be presented in this chapter:

•

When you

of shell programming consists of

of potential patterns, and executing a

requires an understanding of regular expressions, be-

cause a regular expression

The following

list

UNIX command interpreter. The command expressions is called a

how

UNIX

to

this chapter,

make

you should be able

a language regular,

why

to tell

in

a

regular expressions

and when they are used. You should be able

examples of different uses of regular expressions

when

to provide

UNIX commands,

and you

egrep. awk. and sed scripts. egrep. awk. and sed are. when they are

should be able to use regular expressions in

You

should be able to describe what

useful,

what

their differences are.

and you should be able

to write simple to

399

400

Chapter 12 Regular Expressions and Scripts

Chl JL

awk and sed scripts. The

moderate found

"UNIX /Chi 2"

in the

examples

illustrated in this chapter

can be

directory and can be executed and modified to

help you learn the material.

Before discussing regular expressions and their uses it is

know

informative to

can create a

that a shell script

UNIX commands

of

need not be complicated

and execute

all

at all.

You

of them by executing the

the shell environment. For example, create a file called

file in

per"

file

programming.

in shell

"LatexAPa-

that contains the following six lines:

latex paperfile; bibtex paperfile; make index paperfile; latex paperfile; dvi2ps paperfile > paperout.ps

You

can

now

execute

all

of these processes by entering the single com-

mand: localhost> /bin/csh LatexAPaper &

where

per

is

"paperfile tex" .

a simple shell script.

mands and

utilities,

All the script does

and

is

is

that the user

debugging output

ample

is

is

that the file,

command

paperfile tex would .

else.

have to

number of commands so

The commands

can perform other tasks. In

exist.

that

you

are executed in the back-

this

example, however, the

displayed to the standard output anyway. This simple ex-

the essence of shell

that has a

name of a latex source file. LatexAPacommands are known UNIX com-

that the

sequentially execute a

can continue doing something

ground so

the

Note

programming.

A shell script can be

sequence that you have a

difficult

a

one

line file

time remembering, or

can be an extremely complex program. Start small and work your

way

it

up.

12.2 Regular Expressions An

expression defines a relationship between operations and the objects they

operate on.

which are

A

regular expression

legal

ular language.

is

one

in

which

the operations are those

on regular languages, and the objects are the words in the regresult of a regular expression is a set of words which would

The

match the original expression, and forms the basis for pattern matching in UNIX. Regular languages form the basis lor all computer programming languages, so their scope extends beyond that of

UNIX. For that

reason, a shallow

discussion of the mathematical basis of regular languages and expressions pre-

cede our discussion of their use

sed. and

egrep

in shell

programming. The

UNIX

are introduced at the end of the chapter.

utilities

You have

awk.

alread)

Regular Expressions

12.2

been using regular expressions

Chl2

in

401

many commands,

so try to view the followyou have seen or can look up. Regular exvi. egrep. and find for pattern matching

ing discussion in terms of examples

pressions are used in utilities like

while searching for strings. regular

Mathematical Background

12.2.1

A

Let

be a

of characters called an alphabet.

finite set

A word

is

a string of

characters from A. For example, "aab." "abc." "ccc." and "babbc" are in the

standard alphabet, because they are

from the standard alphabet. There

is

which has no characters. This word

A i: = L2 = L3 =

{a,

bb, aa,

{e,

ab}

{a,

language

acab} aaa.

is

all

also a special

word called

will be designated with

the

empty word

an "e."

a set or collection of words. For example:

are all languages. Notice that

some languages

are finite (e.g.,

LI and L3. which

have exactly 3 and 2 elements, respectively) and some are infinite

Given

words

and

}

12.2.2

all

comprised of strings of characters

(e.g.,

L2).

Language Construction Operators a collection of languages, there are

from them using the following

ways

to construct other

languages

set operations:

Union (u) Intersection (n)

Difference (-)

Concatenation Star closure

1

.

We

will use

A

=

{

a

,

b

,

c

}

(*)

for set

examples

in this section. In

—upper and lowercase alphabetic punctuation, and math symbols. —except newline includes

all

characters

for the

UNIX,

the character set

characters, digits, the blank character, character.

J

402

Chapter 12 Regular Expressions and Scripts

Union The union of languages with. That

is,

the union

is

is

the

same

as the union of sets that

the combination of

languages. For example, suppose that

all

you

are familiar

non-repeated elements of both

Ll and L2

are defined as follows:

Ll = {urchin, starfish, nudibranch} L2 = {dolphin, otter, starfish}

then the union of

Ll

u

L2 =

Ll and L2

is:

starfish, nudibranch, dolphin,

{urchin,

where the

u

symbol

is

otter}

normally used to denote the union operator.

Intersection Similarly, the intersection of languages in

is

the collection of elements repeated

both languages. For example, suppose that

Ll and L2

are defined as fol-

lows:

Ll = L2 =

{pumpkin, zucchini} {tomato, potato, pumpkin}

then the intersection of

Ll

n

L2 =

Ll and L2

is:

{pumpkin}

Again, the

n is the

standard symbol for the intersection operator.

Difference Given two sets, the difference between the sets is arrived at by taking the members of one set which are not members of the other set. For example, suppose that Ll and L2 are defined as follows: Ll L2

:=

==

{school, pool, dog, {pool, snail, tree,

snail} stone}

then the difference between

Ll

--

L2 =

{school,

dog}

Ll and L2

is:

12.2

and the difference between L2 and LI L2

-

Ll =

{tree,

403

is:

stone}

Notice that -

Regular Expressions

set difference is directional, since

Ll

-

L2

is

different than

L2

Ll.

Concatenation Given two words, we concatenate them by placing them together to make a longer word. For example, the concatenation of "school" and "house" is "schoolhouse." The concatenation of "aab" and "cbbba" is "aabcbbba." Note that the concatenation of any word with "e" is the word itself (e.g., "aab" concatenated with "e" is "aab"). We can concatenate two languages by taking

all

possible combinations of concatenations of words in the

guage with words

in the second.

For example,

if

Ll and L2

first lan-

are defined as fol-

lows:

Ll = L2 =

{school, pool, {house, hall}

dog}

then the concatenation of

Ll and L2

is:

L1L2 = {schoolhouse, poolhouse, doghouse, schoolhall, poolhall, doghall}

The concatenation of two languages L1L2).

is

written like an arithmetic product

(i.e.,

Star Closure

New

languages can be constructed by repeating the concatenation operation

any number of times. This operation

is

called *-closure (star closure). For ex-

ample, a language can be concatenated with

itself:

L2L2 = L22 = {househouse, househall, hallhouse, hallhall}

where the notation L2 2 means

that the

language L2

is

concatenated with

itself

J

404

Chapter 12 Regular Expressions and Scripts

(i.e.,

L2L2L2

=

twice) This can be done three times:

L23 = {househousehouse

househousehall, househallhouse, househallhall, hallhousehouse, hallhousehall, hallhallhouse, hallhallhall}

And

,

so on. For any language L,

guage L, denoted L*, a

member

of)

L*

if

it

let

LO =

e}

{

the union of LO, Ll, L2,

is

then, the *-closure of lan-

,

the concatenation of zero or

is

word is in (i.e., more words from L (The

Basically, a

...

zero condition, LO, pertains to {e}).

We

are

regular

if

now

it

ready for the definition of regular languages.

contains only a finite

number of words or

it

A

language

is

can be constructed

from other regular languages using unions, concatenations, or ^-closures. For example, Ll = L2 =

(aa,

if:

bb}

{c}

are languages then: •

Ll and L2

•

L3

are regular because they are finite

Ll*

=

{e, aa, bb, aaaa, aabb,

=

aaaaaa, aaaabb, regular since

is

it

.

.

bbaa, bbbb,

.

the *-closure of regular language

is

Ll

L4= L2L3 = {c caa, ebb, caaaa, caabb, cbbaa ebbbb, caaaaaa,

•

,

.

is

regular since

L5 = L3

•

u

it is

the concatenation of

L4 =

regular since

L6 =

•

it is

(L2*L1 )*

.

L2 and L3

{e, c, aa, caa, bb, ebb, aaaa, caaaa, aabb, caabb, .

is

.

.

the union of regular languages. is

also a regular language.

nation of the *-closure of

L2 with

It is

the ^-closure of the concate-

Ll. Note in this example, that there

is

an "em-

bedding' of one *-closure within another.

12.2.3 In

Regular Expressions

UNIX,

in

Unix

regular expressions are used by

many

utilities to define/identify

ap-

The basic idea is that a regular expression is used as a compared to a large number of character/word strings. When

propriate sets of words.

pattern which

is

is found to be equivalent to the pattern, then it has •'matched.'" or "patmatched" the expression. The set of strings that matches the pattern is a regular language. For example, in the vi editor. there is a substitute com-

a string tern

1

12.2

mand :

for

making a change

Regular Expressions

The syntax

in a line.

for the substitution

405

is:

s/old_text/new_text

Given the

'

:

s'

command,

the editor searches the current line for a string

matching the "old_text" and replaces

with the "new_text." The it compare against sample strings. Notice that the two strings are separated by a slash ( / ). The slash is called a pattern delimiter. The pattern delimiter need not be a slash, but can often be any special symbol as long as the symbol is not a part of either the original pattern string or the

"old_text"

replacement

is

the pattern to

string.

For example,

if

the line:

car is rad

John'

exists in a file

and the vi

command

:s/ra/:re

is

issued while editing the

file,

then the result will be

car is red

John'

In this

example, the search

command could be

modified as follows without

any affect on the result :s#ra#] re

More

generally, the specification of the

"old_text" can be

a regular ex-

match zero or more occurrences of the single character regular expression that precedes it. Note that this is a different usage than the asterisk as a wildcard. It only matches a single character. The pattern "we*k" matches "wk," "wek," "week," "weeek," etc. Suppose the line of text is: pression. For example, the kleene star (*) can be used to

This wk is the last wek in which to purchase a weeek 's supply.

1.

We

ever,

will use

it

vi and

pattern search to illustrate

some

delimiters and

is

not the search

command

itself.

howdemarked by

applications of regular expressions,

should be remembered that the regular expression

is

the statement portion

406

Chapter 12 Regular Expressions and Scripts

Then

:

the

command:

s/we*k/week/g

will produce:

This week is the last week in which to purchase a week's supply.

The "e" must precede the "*" or it will match the "w" instead. The "g" on the end of the command means make the replacements globally, i.e., everywhere in the current line. Without the "g," the substitution will only be made on the

first string that

special

symbols used

matches the

pattern. Besides the *, there are several other

in regular expressions,

some of which

are tabulated be-

low.

Table 12.1: Symbols used in matching regular expressions []

Any all

characters within the brackets will be matched, e.g. [a-z, alphabetic characters in both lower and upper cases

a-z] matches

Matches any single character

One important cial

symbol

Replace the notion of

*

as

note:

one of

its

Sometimes

the pattern to be

matched contains

a spe-

characters. For example, suppose the line of text

is:

with the star closure in this line.

and you wish

to substitute the

"*" with

"*-closure. The command: '

:s/*/*-closure

will not

work, because the

status, called

command i

* is a special

symbol.

escaping the symbol, precede

it

To remove

its

special

symbol

with a backslash (\). The correct

is:

s/ \ * / \ * -closure

The backslash preceding the next character.

the asterisk

means "ignore

the normal

meaning" of

Regular Expressions

12.2

Regular Expressions

12.2.4 Bracketing In the

UNIX commands ed and grep, there is also the

lection of

symbols as a

and can be used

407

unit.

in place

The reference

of the collection.

ability to refer to a col-

is

then called a tag of the collection

To

tag part of an expression, enclose

The parentheses will have to be escaped, so precede each Once a part of an expression is tagged it may be referred to by number based on its ordinal position: 1 refers to the first tagged expression, 2 refers to the second, and so on. The position should be preceded with a it

within parentheses.

with a backslash,

(

\

).

backslash (\). For example, consider the text in the

taggedtest" I

file

"regular/

below:

feel good.

John loves Mary.

Positioning on the

first line in

vi, the following

command

can be issued:

:s/\(good\)/\l \1 \1/

which produces I

feel good good good.

As another exc imple, by positionin g vi on the

third line

and issuing the

fol-

lowing search and replace command: :s/\ (John\) loves \(Mary\)/\2 loves \i/

replaces

John loves Mary.

with

Mary loves John.

12.2.5 Full

Note

Regular Expressions

that not all regular expressions are possible with the special

above.

It is

not possible to

However, with some

embed one

UNIX utilities,

pressions" are possible.

The

* within another

such as

symbols

such as (ab*c)

awk and egrep,

*.

"full regular ex-

additional special symbols used in full expres-

4Uo

Chapter 12 Regular Expressions and Scripts

sions are.

Table 12.2: Symbols used in (

)

full

regular expressions

Parentheses can be used to group part of an expression; for example, a (dog)

matches

a,

adog, adogdog,

Matches one or more occurrences of the regular expression

Matches any character

A

Matches the

$

Matches

the last character

Matches

either of

+

red ?

or

first

that precedes

it

character on a line

on a

line

two patterns separated by

; |

for example,

red rad matches |

rad

Matches zero or one occurrence of the preceding regular expression

Parentheses have precedence over the other symbols, then enation, and, finally,

12.3

*

etc

*

+

?,

concat-

|

egrep The command egrep is

a pattern matcher like

the use of full regular expressions, allows

permits pattern input from a is

to use the

file.

you

The way

gr ep and f gr ep,

but

it

allows

to specify several patterns,

and

from a

file

to specify pattern input

'-f option. For example: '

egrep -f patfile searchfile will search the

"searchfile"

using patterns in the

"patfile." As another

example:

localhost> egrep -c 'A[0-9]+Q' *.c

will provide a

count (-c option) of the number of lines

contain the pattern "A" followed by any

by a "Q." Each for the

grep

file will

in

each

number of digits

be reported independently. See the

family in Chapter

3,

page 86.

(

[

" .

0-9

c" ]

file

which

+) followed

command

reference

12.4

409

awk

12.4

awk The awk

utility is

an extremely important and useful method for locating and

manipulating information

UNIX commands.

from

highly stylized/ordered data, such as the output

in

Data which

terms of fields and records, so

awk

to scan the lines of a file (or

many

perform an action on those

file.

program on

highly structured

really a field

files)

awk

is

command

line,

often referred to in

awk can

be used

match

match)

(or don't contain a

sent to standard output but can be redi-

There are two formats for awk: the

the

is

matcher,

looking for a particular pattern and

lines that contain a

of the pattern. The output from rected to a

is

is

while the second takes

awk

takes an

first

it

from a

script/

We

file.

ad-

dress the command-line version, because understanding one will be enough to

understand and use the other.

awk script [file-list] The "script" above

refers to an

awk

An awk

script.

script is a

sequence of

pattern/action pairs:

pattern {action} The

pattern

the line.

used

is

and the action

Both patterns and actions are optional.

generic form, then

then

to select lines to analyze,

awk

If a pattern is

selects all lines of the input

file. If

is

"pattern"

is

analyze

to

missing from

an action

awk performs the default action of print, which copies the

output (most often the display). Each

used

is

this

missing,

line to standard

a regular expression en-

closed in slashes (/). Actions can be quite complex, and entire books are de-

voted to

awk

script writing (see Section 14.8).

A large subset of C

can be used as actions. Actions are always enclosed Note: it is

It is

a

good idea

to place the entire script in single

not confused with shell

long listing as input. First redirected to a

file

in curly

commands. Here

let's

look

at the

called "f oo" using

are

quotes

(

'

'

( { )

} ).

so that

some examples which use

long directory

tee.

instructions

braces

listing,

which

I

a

have

410

Chapter 12 Regular Expressions and Scripts

localhost> Is total 361

-

-rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rw-r- — r--rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rw-r-rwxr--xr-x -rwxr- -xr-x -rw-r- --r--rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rw-r- --r— -rwxr- -xr-x -rwxr- -xr-x

jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges

—r—

1

1 1 1

1 1 1

1 1 1

1

1 1 1

1 1 1

1 1 1

1 1 1

1

1 1

|

tee foo

Note

5731 15826 21794 2303 40798 689 12723 14287 15017 23280 7693 15947 5369 2233 1685 5521

Mar Mar Jan Jan Mar Mar Aug Aug May May May May May

Oct Oct Sep Jan 5437 Apr 6326 Jun 12726 Aug 14287 Aug 7224 Jun 63235 Jun 12722 Aug 14287 Feb 30639 Jun

that

tee

23 21 6 6

23 23 12 12 16

16 16 16 16 19 19 11 29 30 21 12 12

21 4

12 1

21

1989 1989 1990 1990 1989 1989 12:15 12:15 1990 1990 1990 1990 1990 1990 1990 1990 18:15 1989 1991 12:13 12:15 1991 1990 12:10 1990 1991

reserved a

rectory before completing the listing is

always expect

awk

.

.

.

.

.

.

.

foo jack. sty

©

mitthesis sty sf suletter sty sf suseal .ps sf suthesis sty texinfo. tex uclaletter sty ucseal .ps ucthesis sty .

.

.

.

.

name and location (at item 1) in the current dicommand. Also recall that the long directory

extremely structured. Every line follows the same format, so you can to find similar information in a similar location. This is the kind

of information which ple

aaai sty alpha4 .bst apalike.bst apalike. sty cite .bst cite. sty csuletter sty csuseal .ps diss .bst diss doc diss sty dissl2 .doc dissl2 sty disstitle.doc disstitle sty doublespace sty

script

on

is

ideal for

this file.

awk,

as

you

will see.

Now we can issue a sim-

12.4

localhost> awk total 361 -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rw-r- __ r __ -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rw-r- --r--rwxr- -xr-x -rwxr- -xr-x -rw-r- r~ -rwxr- -xr-x -rwxr- -xr-x -rwxr- -xr-x -rw-r- --r--rwxr- -xr-x -rwxr- -xr-x

—

1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1

1 1 1 1 1

1 1 1 1 1

'

{print}

'

411

foo

Mar Mar Jan Jan Mar 689 Mar 12723 Aug 14287 Aug 15017 May23280 May 7693 May 15947 May 5369 May 2233 Oct

jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges jhodges

awk

5731 15826 21794 2303 40798

23

21 6 6

23 23 12 12

16 16 16 16 16

19 1685 Oct 19 5521 Sep 11

5437 6326 12726 14287 7224 63235 12722 14287 30639

Jan Apr Jun Aug Aug Jun Jun Aug Feb Jun

29 30 21 12 12 21 4

12 1

21

aaai sty alpha4 bst apalike .bst apalike sty cite .bst cite sty csuletter sty csuseal ps diss .bst diss doc diss sty dissl2 .doc dissl2 sty disstitle doc disstitle sty doublespace sty

1989 1989 1990 1990 1989 1989 12:15 12:15 1990 1990 1990 1990 1990 1990 1990 1990 18:15 1989 1991 12:13 12:15 1991 1990 12:10 1990 1991

.

.

.

.

.

.

.

.

.

.

.

.

foo jack. sty

mitthesis sty sfsuletter.sty sf suseal .ps sf suthesis sty texinf o tex uclaletter.sty ucseal .ps ucthesis sty .

.

.

.

This ultra simple script has no pattern and only the simplest of actions, reads and prints the entire script

file,

one

it

The next most simple awk simple pattern match test and an

line at a time.

does almost the same thing, but has a

action to print the result

localhost> awk foo /cite. bst/ {print} -rwxr-xr-x 1 jhodges 40798 Mar 23 1989 cite. bst '

'

The pattern matches all lines in the file "foo" which contain the string "cite. bst" (note the use of slash delimiters, which are used to bound a string), and sends these lines to standard output. Because the contents of foo is

a directory listing, and since there

name, the 12.4.1

The

script output is

awk and

real strength

is

only one item

comprised of a single

in this directory

with that

line.

Field Variables

of awk

is

how it works

with structured data.

A data file called

J

412

Chapter 12 Regular Expressions and Script*

shown below. Each of the columns is separated by empty space, so easy to look at and compare each column, awk has a facility for looking at these columns, or fields, by identifying the column separator and the column number the item is associated with. As a default, awk denotes fields as items separated by spaces. Each column, or field, is associated with a number,

"data"

it is

and

is

referenced with a leading dollar sign ($). For example, wherever the no-

tation

Below data: 237 422 371 345 323

$3

is

seen in the

awk

script

below, the third field

-"

is

being referenced.

rows of four numbers, called

are the contents of a file that has five

7

— —

37 embedded in field #1 of line #1 22 embedded in field #1 of line #2 37 embedded in field #1 of line #3

8

-

37

19 28 12

85 48 16 8 8

67

89 37

19

is

fairly

Below

is

an

awk

script

is

field

which matches '37' and

#3 of

/37/ {print $1} 1221 {print $3}

'

'

#5

'22.' If a '37'

where in a row, then the script will print the first field in found in a row, then the script will print the third field in

localhost> awk

line

is

found any-

that row. If a '22'

data

237

-"

field #1 of line

16

-

field

#3 of

line

371

field #1 of line

323

field

In the if the

example above, the

field

where the match occurs

UNIX

example using

then both actions will be executed. fields in the action part of

localhost> awk /.ps/ {print $4} /.doc/ {print $4, $8} 23280 diss. doc 14287 15947 dissl2.doc 223 3disstitle.doc 14287 14287 '

The all

I.

by

Note

awk

that the

'.'

is

as a period.

# 1 of

is

line

lines

input

file

for this

which contain

"

example

.ps."

not a special character unless

1

it

is

Now

both a

foo

again "foo." The

escaped. Because

if

let's return to

first

pattern matches

and the second pattern matches

is

#2 #3 #5

-1" example.

our "Is

'

#1

not specified, so

pattern occurs in any field, the action will be executed. In addition,

patterns are matched,

is

that row:

it

is

not.

it

is

all lines

which

interpreted

12.4

contain

" .

doc."

If the line

awk

matches either pattern, then the action

says to print the fourth field in the

line. If the test is true for

" .

413

print $4 awk

doc," then

As a result, awk is extremely useful for manipulatof UNIX commands, because they are always very structured.

also prints the eighth field.

ing the results

The use of fields

in

awk scripts can also be applied to files with different field awk has an optional argument, '-Fc, that allows the

delimiters (separators),

user to define which character "c" will be treated as the field separator.

example, you are trying

to

analyze a

"test," whose

file,

If,

for

fields are separated

by colons, as follows:

localhost> cat test bob: ted:mary :alice :baz :bar :dog: fish: snail cloud :

then your

localhost> awk -F: baz bar

'

awk

script

could identify each field as follows:

/mary/ {print $5} /ted/{print $6}

test

'

field separator In this example,

which happens,

when awk

in this case, to

"mary,"

finds a

prints out the sixth field, which, in this case,

they are on the same line in the

12.4.2

values of fields.

"bar."

is

'

awk make

In this

by adding a logical

finds a "ted,"

it

decisions about what to do based on the

to

work.

easily have tied the

either"

foo

'

example, the two vertical bars

need not be capitalized

we could

test to the conditional:

/.doc/ {print $4, $8}

ator, so the conditional is true if

'F*

it

doesn't matter that

A logical test may take the form of conjunction, a disjunction,

tests together

localhost> awk /.ps/ 14287 csuseal.ps 23280 diss. doc 15947 dissl2.doc 2233 disstitle.doc 14287 sfsuseal.ps 14287 ucseal.ps

The

It

file.

or a negation. Returning to the "f oo" example,

1.

prints out the fifth field,

awk and Logical Tests

Often one will want to have

two

it

be "baz." Likewise, when

.

(

) |

represent the logical

|

ps"

or

"

.doc"

is

OR oper-

on aline of "foo."

414

Chapter 12 Regular Expressions and Scripts

have changed the action

was to show how The other logical operator you might use is the AND, or conjunction, operator, which is the double-ampersand (&&). Notice that

I

slightly, but the intent

the logical operator works.

Formatted Output

12.4.3

awk

allows the programmer to

extension

is

make use of commands

printf (see Section 8.3.4,

page 278).

We

other than print.

C programming

to control the format of output using the

One

function

can apply the same example using

printf, as follows:

localhost> awk The The The The The The

file file file file file file

size size size size size size

is is is is is is

/.doc/ {printf "The file size is: %d, the file name is %15s", $4, the file name is csuseal.ps the file name isdiss.doc the file name isdissl2.doc the file name is disstitle.doc the file name is sfsuseal.ps the file name is ucseal.ps

/.ps/

'

:

:

:

|

14287 23280 15947 2233, 14287 14287

The

printf

and the

size of the space allocated for printing the field value.

means

and by not specifying

size the entire

its

to print a string of 15 characters,

In this case, is,

more

fo
"footmp"}

localhost> more footmp The file size is: 14287, the file name is csuseal.ps The file size is: 23280, the file name isdiss.doc The file size is: 15947, the file name isdissl2.doc The file size is: 2233, the file name is disstitle.doc The file size is: 14287, the file name is sfsuseal.ps The file size is: 14287, the file name is ucseal.ps

'

foo

awk

and

awk

12.4

The component of the awk

script associated with the redirection has

bolded. Notice that the redirection

not create the long directory listing

is

quoted. Finally, what

first,

directly into the

it

been

performed within the action part of the

is

awk statement and that the filename ed, instead, to pipe

415

we would rather

-1 command, but want-

with the Is

awk

if

This can also be done easily,

script.

as follows:

localhost> Is -1

awk '/.ps/

|

/.doc/ {printf "The file size is: %d, the file name is %15s", $4, $8 >"footmpl"} '

localhost> more footmpl The file size is: 14287, The file size is: 23280, The file size is: 15947, The file size is: 2233, The file size is: 14287, The file size is: 14287,

the file name is csuseal.ps the file name isdiss.doc the file name isdissl2.doc the file name is disstitle.doc the file name is sfsuseal.ps the file name is ucseal.ps

Again, the component of the

awk

doesn't

files,

so you can perform the

if

you

know

awk script associated

the difference

same

are sending the output to a

script to

between a single tasks

temp

on many file,

bolded.

you have

to

list

of

Of course, modify the

awk Test

Field variables can be used in the test part of an in the action part

of the

long directory

this instance,

We

files sequentially.

as above,

is

input and a

append, rather than write, using >>, or some other creative method.

12.4.5 Field Variables in the

4. In a

with the pipe

file as

use the

script. In the

fourth field represents the size of the

listing, the

we want to

test called is

flag

a

any

awk script as well as they are we will look at field number

next example,

file

member

file.

In

with a size between 20 and 100 kilobytes.

of.

which

is

the tilde

symbol

(~).

awk '$4 - [2-9] [0-9] [0-9] [0-9] [0-9] {printf "The file size is: %d, the file name is %15s", $4, $8>"tmplrg"} localhost> more tmplrg The file size is: 21794, the file name is apalike.bst The file size is: 40798, the file name cite.bst The file size is: 23280, the file name diss. doc The file size is: 63235, the file name is texinfo.tex The file size is: 30639, the file name is ucthesis.sty localhost> Is -1

I

'

In this (size) field

matches the pattern

between

and

selected.

The

9,

or a

action

is

file

Is

-1

in which the fourth between 2 and 9 followed by four digits wholse size is between 20 and 100 Kilobytes) are

example, those lines from the

listing

(a digit

to print the

same

size

and name as before. The same ex-

4 ID

Chapter 12 Regular Expressions and Scripts

ample can also be performed with

localhost> Is -1

inequalities, as

shown below.

awk '$4 >= 20000 && $4 < 100000 {printf "The file size is: %d, the file name %15s", $4, $8>"tmplrg"} localhost> more tmplrg The file size is: 21794, the file name is apalike.bst The file size is: 40798, the file name cite.bst The file size is: 23280, the file name diss. doc The file size is: 63235, the file name is texinfo.tex The file size is: 30639, the file name is ucthesis.sty |

is

'

In this example,

and

we used

12.4.6 Shell Variables

As a final

own

AND operator (&&).

and awk

illustration of the strength of

ables from outside an its

both inequalities for greater than or equal to (>=)

less than ( echo awktestsv set filenamel = $1 set filename2 = $2 awk / "$filename2" '

n

'

4

/

{print $4,

$f ilenamel

$1

ii

evaluate in shell parse

unparse

unparse

parse

$f ilenamel has the value "foo," and $f ilename2 has "diss bst," then this print produces the following: If

the value

.

localhost> awktestsv foo diss. bst 15017 diss. bst

where the

first

column of

the output

is

the file si/e

and the second

is

the file

417

sed

12.5

name, as expected. This example can be confusing, because, as a beginner, you

do not

know how

really

double quote

is for.

the single quote

The

single quote

and the second means script,

The balanced quotes

argument and return

first

quote

you can

start

its

command

will be

indicate pars-

tells to start

to stop parsing (zmparse)

and go back

to

and stop quoting any-

depending on what you are trying

tells the shell's

awk what

used to identify to will not.

interpreting in the shell environment. So,

where within the double quote

being used by awk, nor what the

parsed (interpreted) by awk. The

the script to be

ing the script,

is

what

interpreted as part of the script and

is

to accomplish.

The

interpreter to evaluate the associated

value. Thus, the effect of the single and then double

quotes surrounding the shell variable

$f ilename2

and then

to interpret the variable as a field,

is

to tell

awk

to evaluate the variable

to not try

and return

the value to this location in the script.

Sometimes you find yourself in a position of wondering if you could concatenate a field from the awk test with the value of a shell variable. In such a case, you can use a similar tactic as above. Consider a case where you want to concatenate the

name of

a file with the value of the

HOME

shell variable.

This

can be done as follows:

localhost> awk '/.tex/ {print /usr/f 1/ jhodges/texinfo tex

"

'/"$8}

"$HOME"

'

'

foo

.

Now awk is

is

being told to print a string, but just after the string argument

started, the script is unparsed.

by the

shell,

Then $HOME

is

ignored by

awk and evaluated

before starting the script parsing again. Finally, the string argu-

ment is ended with a /' which is followed by the name of the file in field 8. The interesting thing going on is the string conversion in awk. Note that the '

last slash is

located inside the string double quotes, just prior to concatenating

with the field variable. Also note that spacing has been provided, around "

12.5

$HOME."

for clarity, but should not be used to

produce the desired output.

sed sed

is

called a

stream editor and

patterns and manipulating them. erate terns.

on

is

It is

an important and useful tool different than

fields but. rather, allows editing

What sed does

is

to take a list

awk because

commands

to

it

in selecting

doesn't op-

be used on general pat-

of patterns line by

line,

much

as does

awk, and executes a set of actions on them. The editing actions which sed uses are the same as the global editing commands in vi. They work with regular expressions and allow offline

(i.e..

not using an editor) editing of

will edit lines of a file according to a specified script.

the results to the standard output,

sed

By

default,

has two formats, like awk.

files,

sed The

sed

sends first is

4lO

Chapter 12 Regular Expressions and Scripts

to take the script

on the command

line as follows.

sed script [file-list] where the editing commands in the script are applied to all lines in the each of "file- list." The second format uses an option '-f to lo-

the files in the

cate the script in a

file:

sed -f scriptfile [file-list] in

which the editing commands are stored in the file "scriptfile." A or "scriptfile" contains one or more lines in the following

"script" form:

[address

[,

address]] instruction {argument -list} The "address" may be line numbers in the file. In general, any global command you would use in vi to find a line can be used to specify an address in sed. Addresses in sed are optional. If only one is specified, then that line is edited. If two addresses are specified (separated by a comma), then that range of lines is edited. The address may also be regular expressions, in which case those lines which match the pattern are selected. If addresses are not specified, then sed edits all lines. As a simple example using sed, consider the following

file:

localhost> more test When I was a boy we had a dog named Greta. I have no idea how we were supposed to spell that dog's name, I was really quite young. Dogonit, you'd think I would have learned something about dogs by now. I think I've owned a dog almost my entire adult life.

__^_

t_

Suppose you want

to replace all occurrences of a particular string, like

"dog," regardless of case, with "Llama," for a specified range of file.

You could do

lines in a

so as follows:

localhost> sed '1,$ s/ [dD] [oO] [gG] /Llama/g' test When I was a boy we had a Llama named Greta I have no idea how we were supposed to spell that Llama's name, I was really quite young. Llamaonit, you'd think I would have learned something about Llamas by now. I think I've owned a Llama almost my entire adult life. .

Note

that the script, as in

ponent of the script

is

awk.

is

enclosed

in single quotes.

The

used to identify the pertinent range of lines

first

com-

in the file. In

sed

12.5

this case, the lines

the entire file

is

from the

analyzed.

first

(1) to the last ($) inclusive are included, so

The second component of the

perform. In this case the global search and replace also the 'g' at the is

end which

tells

just as easy to input the script

419

sed

from a

script is the action to

command

is

used. Notice

to replace all occurrences

on a

line. It

file.

localhost> sed -f sedfile *.cl

where the sample "sedfile" contains the

line

shown below:

localhost> cat sedfile S/"\-/%;/

Note

first that

the file-list '

A

'

is all files

with a '.cl' extension. The

sed

each semicolon at the beginning of a line with a percent-sign (%). As an illustration, consider the sample lisp file bescript uses the instruction

to replace

low:

localhost> more shortlispf ile2 .cl 1st is nil, return 1st 1st is single atom, return 1st car 1st is atom, return car 1st cons ed to flatten of cdr 1st car 1st is list, return flatten car 1st appended to flatten cdr 1st '

(defun fltn (1st) (cond start conditional ((null 1st) 1st) end conditional (atom (car 1st) (cons (car 1st) (fltn (cdr 1st)))) (t (append (fltn (car 1st)) (fltn (cdr 1st)))))) ;

;

(

(defun bob

(x)

(+

x

3)

We can use the template le2 cl" .

as follows.

and the

file,

or

list

of

files,

on

"shortlispf i-

420

Chapter 12 Regular Expressions and Scripts

localhost> sed -f sedfile *.cl 1st is nil, return 1st 1st is single atom, return 1st car 1st is atom, return car 1st cons'ed to flatten of cdr 1st car 1st is list, return flatten car 1st appended to flatten cdr 1st (defun fltn (1st) (cond start conditional ((null 1st) 1st) end conditional (atom (car 1st) (cons (car 1st) (fltn (cdr 1st)))) (t (append (fltn (car 1st)) (fltn (cdr 1st)))))) ;

;

(

(defun bob

(x)

(+

x

3)

Note

that

because the

semicolons

test

only mentioned the

12.5.1 Selection of Line

first

Ranges

sed example we

In the first

would not be affected by column of every line.

in other locations

in

sed

selected the entire file for output. Often

working with the output of UNIX commands you of the total

mand

number of lines

will display a

you want

to

forms

localhost> ps uxa

|

command

heading before

awk you

that function for

need

response. For example, a

listing the

when

be working with a subset

ps com-

processes and their attributes. If to the

to eliminate that first line.

ps command,

The

script

then

below per-

you using sed.

sed -n '2,$ p'

In the

in the

will

perform some analysis on the response

in order to use

this script

|

example above,

awk '{print $1, $10}'

a

number of new tools are introduced. Most imporwhich means "do not print anything which does

tantly, the '-n' option is used,

not meet the criterion of the match". Then, in the script, anything

turned must be explicitly printed. This

of the script process

is

name

why

the 'p'

is

we want

re-

used. Finally, the result

piped into awk, which prints the process owner userid and the (fields 1

and 10). Below

localhost> ps uxa sed -n '2,$ p' jhodges ps jorge rtin geisman /usr/ local /lib/mocka/sys/Mc jhodges azhao pine-exe vcsc3081 vi jhodges sed |

is

|

is

a sample run of this script.

awk '{print $1, $10}'

12.5

12.5.2

Regular Expressions

sed will The

script

'

421

sed Tests

allow the use of regular expressions in the selection of string patterns.

below looks for a number use of bracket

illustrates the

.ocalhoso sed -n

in

sed

[0-9]

(

[

]

in

)

in the first

sed

column of

the input file

and

scripts.

p'

12.5.3 Shell Variables in

As with awk.

it

will often

sed

Scripts

be important to use a shell variable to select a pattern

sed. The script below shows that, to perform this kind of task, same mechanism that was used in awk also works for sed. Particularly,

for analysis in

the

one doesn't quote that portion of the

and then the quote

is

script

used to identify the shell variable,

again begun, or restarted. This example selects patterns

which include the value of the

shell variable

"third".

localhost> sed -n $third' p'

Unlike awk.

sed does

not

work with

field variables, so there is

no confu-

sion in referencing the shell variable in the script, but the parsing of the script

must

still

12.5.4

be turned off while the shell variable

interpreted.

sed Option Reference

Table 12.3

how

is

to use

is

an abridged table of

sed

sed options which may be useful

in learning

effectively.

i

422

Chapter 12 Regular Expressions and Scripts

Table 12.3:

sed Command

options reference

N

Append

the next line of input to the selected

patterns with an

P

embedded new

line

Print the selected patterns to the standard out-

put

q

Go

r RFILE

Read

s/test_pat/new_string/options

Search and replace. Any character may be used instead of 7' options are zero or more of:

to the

end of the

script

the contents of file

rfile

;

g

p

Global change on a

line

Print the selected patterns if a

replacement was made

w wfile

w fname

Append the selected patterns to wfile if a replacement was made Append the FNAME

selected patterns

to

y/stringl/string2

Replace the characters

in

corresponding characters lengths of

stringl

stringl with in

string2;

the

the

and string2 must be

equal !

-function

Apply the function only

to lines not selected

by the addresses

Place the current line

output as a line

number on

the standard

Exercises and Sample Quiz Questions

12.6

12.6 Exercises

423

and Sample Quiz Questions

12.6.1 Exercises Exercise

1

Let

Ll =

{aa, bbb} and L2

=

{cc}.

What

is

the union of

•

What

is

the intersection of

•

What

is

the concatenation of

Ll and L2 (Ll

u L2)?

Ll and L2 (Ll n L2)? Ll and L2 (L1L2 )?

WhatisL2*° Exercise 2

Practice with each of the special symbols. '..'"[ '$*

in different

amples are the Exercise 3

Create a

file

UNIX commands

grep

family,

Some

and regular expressions.

ex-

find. Is, cp and rm.

with three columns of numbers. Write an

prints the third number on each

which

].*'*.' '\,' and

line in

awk command

which the

first

number

is

larger than the second.

Exercise 4

Exercise 5

Write a combination sed/awk script that takes the output from the UNIX w command and prints out only the first 10 users (alphabetically) and what processes they are running. You can use the head com-

mand

for this exercise.

Copy

the lines below into a

ing the

word "know"

file.

Use sed

into a line that reads

to

change

all

lines contain-

"Why not?" You

need

will

a scriptfile.

I I I I I

I

12.6.2 Problem

stayed up late. know I shouldn't have. ate too much. know this is bad for me. will be better in the future. don't know if this is possible.

Sample Quiz Questions 1

Why

are regular expressions a useful tool for

examples which

Problem 2

illustrate

UNIX

users? Give two

your answer.

Use a regular expression and the find command to locate all files below your current directory which end with some extension, like c,' '

.

and print them.

Problem 3

You have

to transfer a number of files from a Macintosh to the local The Macintosh file system separates directories with colons, as host. shown on the first line below. You want to convert the Macintosh file

system into your

UNIX

file

system, so that your

same way on both machines. What utility and why? Write the line of code which

is

files are

most useful

organized the for this task,

will translate a file called

424

Chapter 12 Regular Expressions and Scripts

"f ilein" with

on

file

paths of exactly four directories to the form

below. Write the output to a

line 2

file

shown

called "f ileout."

Documents: Classes: UNIX: Manual :Man2 tex Documents/Classes/UNIX/Manual/Man2 .tex .

Problem 4

Write a

sed program

that looks through every file in the current di-

rectory and replaces every occurrence of "got a fair trial" with "got an unfair

Problem 5

Explain what "escaping" a character means, and essary.

Problem 6

trial."

when

its

use

is

nec-

Give an example.

Write an

awk

script that takes the output of the command Is - 1 and named "foo" which contains the names and sizes of whose size exceeds 100 kilobytes. Sample input is shown

returns a file

those files

below: %

Is -1

-rw-r--r--

1

-rw-r--r—

1

-rw-r--r--

1

-rw-r~r~

1

Problem 7

613633 May 14 13:44 All.ps 463 May 14 13:43 ModulellABCD. aux 13374 Apr 30 1992 ModulellABCD.tex 463 May 14 13:43 Modulel2ABCD.aux

hodges hodges hodges hodges

Consider the two regular languages. LI and L2. below. Present an ex-

ample of concatenation.

Problem

8

•

LI:

{

ant,spider.beetle

•

L2:

{

hill,web,juice

Write an

awk

mand and and #8).

script

}

}

which takes as input the output from the w comlist of users and what they are doing (fields #1

returns the

Chapter 13

C

13.1

Introduction and When

a user issues

Shell Scripts

Scope

commands

or

command

sequences

executing programs, and the arguments they give

ments

to the

this sort

at the

program. In the case of interactive dialog

of program execution

is

in the

C

shell,

they are

keyboard are the arguin the

similar to interpreter-based

command

shell,

programming

lan-

guages such as Lisp. In interpreter-based programming languages, expressions are typed at the keyboard, evaluated by an expression interpreter, and re-

C shell and Bourne shell can be used programming interpreters. As with most programming languages, the expressions which can be evaluated by the shell environment are potentially more complex than a user might wish to type at a keyboard; certainly more so than they would want to type repetitively. For this reason, commands sponses are returned on the display. The

as high-level

can be written into a file is

file

and executed

in the shell

environment. The resulting

computer program, a shell script a user doesn't wish to type over and

called a shell script. Also similar to a

can be as simple as a single over, and

it

command

that

can be as complex as any program

in

any programming language.

A shell script can take many forms. The most simple form is typing a command sequence directly at the shell prompt. A shell script can also be a file with a sequence of commands that is executed like a program. You have already been introduced to many shell scripts in the form of initialization (dot) files. In Chapter 5. the special login scripts, ".login" and ".cshrc," were introduced and discussed. Both files are C shell scripts. In addition, many other dot files (e.g., ".logout," ".vacation," ".mailrc," ".newsrc," " .

exrc." ".profile."

etc.) are also shell scripts

which are executed along

425

426

Chapter 13 C Shell Scripts

own

with their

initiate a utility,

and

which newsgroups

Each command the

it is

and each

is

file is a script

will be read.

command

shell that a user creates has a

the default login shell

times

dot

is

utility's functionality.

fines

A

which is called to where a user defines variable values and customizes a For example, the file ".newsrc" file is where the user de-

special environments.

Bourne

C

the

is

shell.

shell, as

interpreter. Often,

has been assumed in this

There are many different kinds of shell

optimized for different kinds of tasks. In

C

this chapter,

Some-

text.

interpreters,

you

will be

(/bin/csh). Scripts executed in the Bourne shell are introduced in Chapter 14. One advantage the C shell has over the Bourne shell is that it can work with digit strings as if they were numbers. Another is that the command syntax is more similar to the C programming language. The notions of shell variables and scripts are common introduced to writing scripts for execution in the

to

any

has

shell

own

its

shell

environment; however, each environment syntax, so the

C

shell

and Bourne

shell

is

slightly different

and

envinronments will be pre-

sented independently. The following topics will be covered in this chapter: •

Script execution

•

Script variables

•

Script arguments

•

Script creation

•

Script control structures

On

completion of

of scripts, executed,

how how

this chapter,

they are created,

you should be comfortable with

how

they are

made

executable,

the notion

how

they are

how to perform different You should be able to write

variables are defined and accessed,

kinds of operations, and

how

to

perform

iteration.

which manipulate and execute simple UNIX commands, to incorporate the use of the sed and awk utilities in your scripts. If you need to see the source code for examples shown in this chapter, they can be found in the "UNIX /Chi 3" directory. simple

Chl3

C

shell scripts

and you should be able

13.2

C

Shell Script Execution When you

write a shell script,

it

must be executed

in the shell

environment for

was written. You can invoke a C shell script at the command line. Of course, if you are currently executing commands in a C shell this is obvious. But if you are currently executing commands in a Bourne shell, you could tell which

it

the shell to execute following

commands

in the

C

shell.

To know what

to do,

you must be able to recognize the prompt that signifies one shell over another. The prompt that is used by your computer system indicates which shell is operating. Almost always the default prompt for the Bourne shell is a dollar sign. $. and the default prompt for the C shell involves either a percent sign. %. or a

C

13.3

427

Shell Script Variables

you modify your login shell prompt, then you should you can still recognize the difference between different shell environments. Suppose that you are normally working in the Bourne shell and want to execute a set of commands in the C shell, you would invoke the shell greater than sign >. If

make

sure that

csh command

with the

_.

.

_

_

/bin/csh command

as follows:

initiates the C , , .„ shell on „"command"

-«

.

command

This cuted.

will create a subshell in

The process of creating

shell is a child

is

shell.

completed, control returns to the parent

is

new

which

will execute all

exit the shell. This

is

will be exe-

called forking a shell, and the new-

process of the current, or parent,

execution shell

a subshell

which the commands

commands

in the

When

shell.

the

command

You can

also fork a

new environment

until

you

done as follows:

/bin/csh

When is

13.3

C

this

command

executed.

To

is

issued, the dot-file associated with the

return to the parent or calling shell, type

C

shell (.cshrc)

.

Shell Script Variables One

of the most important notions of a shell script

is

the shell variable.

As

in

any program, the arguments which are provided by the user, and the values

must be associated with variables which can be addressed and manipulated by the user. There are two variable types used in shell scripts: (1) string variables, and (2) numeric variables. In addition, variables used within the

script,

can be defined three ways: (1) within the shell. (2) automatically as shell command line arguments, or (3) as environment variables. 13.3.1 Assigning In the

C

and Referencing String Variables

shell, string variables are

set command.

assigned a value with the

For example, the shell variable named "f ilen." below,

is

a string variable:

sec filen = Unix-Man. tex

Note

that the syntax allows spaces

assignment

character. =.

en't required. shell

between the variable name, filen. the

and the variable value,

The name "set"

is

"Unix-Man tex." They arC and Bourne .

required. Variables in both the

environments are referenced by preceding the variable name with a dollar

sign. $.

For example, the variable

echoed

or displayed.

filen

has been defined and can

now be

428

Chapter 13 C Shell Scripts

localhost> echo $filen Unix-Man. tex localhost> tail $filen % \appendix { answtoexs % \ include { answtoexs % \ appendix { \ latex Examples} % \ include { LatexExamples %\printindex %\bibliographystyle{apalike} %\bibliography {unixmanual % \ end { document

and Referencing Numeric Variables

13.3.2 Assigning

Numeric variables are assigned values with the @ command. For example, you might be looping through a command sequence, and the looping may continue until a shell variable called "total" reaches some value. The total '

'

variable can be incremented as follows:

@

total

=

(

$total

+

1

)

or

@

total++

The

latter

example (++

after the variable

increment operator (see Table In either case,

it is

variable name.

It is

integers, so the

@

9.3,

name total)

is

"Assignment operators

important to keep a space between the equally important to

remember

that

called the in

C

postfix

C," on page 315).

at sign

(@) and

the

numeric variables are

cannot be used to perform operations on double type vari-

ables.

13.3.3

Many When

Command

Line Arguments as Shell Variables

shell variables will

a script

is

called,

be defined implicitly through the script invocation.

any

fined as local variables, with

command

line

names $1, $2

arguments are automatically de$9. They can be redefined

in-

side the shell to be called something different, and they can be referenced with-

any other shell variable. For example, suppose you want to which takes two arguments at the command line. Each argument will automatically be assigned a numeric variable name associated with its order in the argument list. The following script echos the values assigned to two in the shell like

write a script

C

13.4

command

line

Shell Script

Arguments

429

arguments, regardless of what they are

— #!/bin/csh # A script that takes two command line arguments and echos them

(T)

echo $1 echo $2

The line labeled item (1) has significance worth mentioning now. Normally, a pound sign denotes a comment line. However, when the pound sign is followed by an exclamation point and a shell path, on line 1, it forces the script to be evaluated script in the

in that shell.

C

an example of

shell.

how

Thus, item (1)

Assuming

this

that

is

we have

simple script

is

telling the shell to evaluate this

called this script

"echoargs,"

used follows:

localhost> echoargs pink elephants pink elephants

13.3.4

Environment Shell Variables

There are many

shell variables that take

on special values from the environ-

ment, or can be set by the user. For example, the variables HOME. USER,

MAIL, HOST and TERM

are

all

environment variables, which can be

global

referred to in any shell script.

13.4

C

Shell Script

Arguments

Many shell scripts get their input from the user at the shell prompt, while others may get it from the user at execution time. When a script is invoked with arguments

it

looks as follows:

script args where "args" are the required arguments of the

script. Internally, the user-

provided arguments are ordered by their appearance

at the

command

line, as

mentioned above, and referenced with a dollar sign ($) and their ordinate position. For example, suppose we write a script called "phones csh," which .

searches a

file

named "addresses"

number. Simple enough. The

"name" $1

script

for a

"name" and

returns the telephone

keeps track of the variable by calling

430

Chapter 13 C Shell Scripts

localhost> cat phones. csh #! /bin/csh #look up a name in a phone directory fgrep $1 $HOME/addresses

Consider a sample piece of an

"addresses"

file

below.

localhost> more addresses

USHGA: P.O. Box 8300 Colorado Springs, CO 80933 (719) 632-8300 APA: 25 Goller Place Staten Island, NY 10314 (718) 698-5738

When

the script

is

executed

at the

command

"name" argument, such as "APA," which localhost> phones. csh APA 25 Goller Place Staten Island, NY 10314

APA:

is

(718)

line, the

user provides the

defined within the script as $1:

698-5738

Prompting the User for Arguments

13.4.1

A

script might also obtain information from the user by prompting for it. The most prevalent instance where one uses interrogated input is when you do not want to remember the number of arguments or their order, or when you are writing the script but others will be the predominant users. In such cases, the

user assigns a variable

from the standard

name with the value $ simpleif .csh 5 Texmacros 371 Texmacros localhost> simpleif. csh Texmacros footmpl aaai.sty diss. doc alpha4.bst diss. sty jack. sty mitthesis sty apalike.bst dissl2.doc sf suletter sty apalike.sty dissl2.sty sfsuseal.ps cite.bst disstitle.doc disstitle. sty sf suthesis sty cite. sty csuletter sty doublespace. sty texinfo.tex foo tmplrg csuseal.ps tmplrgl footmp diss.bst .

.

it

is

argu-

executed on the directory

argument's value

gument. The

made

is

used to

not 5

in the

(i.e..

any-

second

test the pattern.

ar-

Af-

can be tested as follows:

tmplrg2endif tmplrg3 uclaletter sty ucseal.ps ucthesis.sty .

.

.

The types of

tests

which can be performed

not related to simple variable and value

tests.

in the

One can

C

shell conditional are

refer to status of files in

13.6

even

the operating system, or the script. Tables 13.1

C

to the

Shell Script Control Structures

number and values

437

input arguments, within

and 13.2 show some of the available options.

Table 13.1: File system logical tests

in

the

C

shell

-r FILE

=>

returns

1

if

the file

named file

is

readable by the user

-w FILE

=>

returns

1

if

the file

named file

is

writable by the user

-x FILE

=>

returns

1

if

the file

named file

is

executable by the user

-O FILE

=>

returns

1

if

the user

-e FILE

=>

returns

1

if

the file

named file

exists

-f FILE

=>

returns

1

if

the file

named file

exists

and

is

a regular file

-d FILE

=>

returns

1

if

the file

named file

exists

and

is

a directory

owns

the file

Table 13.2: Standard variables

named file

in

the

C

shell

$0

=»

calling function

$N

=>

Nth

$*

=»

all

the

command

line

arguments

$@

=>

all

the

command

line

arguments

$#

=>

the

$$

=>

process number (PID) of the current process

$!

=>

process

$?

=>

exit status of the last task

command

name

line

argument value

number of command

line

number (PID) of the

arguments

last

background process

13.6.2 foreach-end in programming is the loop. Loops perform the task of iteration, by executing a series of commands repeatedly. Each time the command sequence is executed is called a cycle or pass.

Probably the most powerful control structure

438

Chapter 13 C Shell Scripts

In order to

make

use of the loop, the programmer must be able to enter

it and begun (entered) when some condition is met, and the loop is ended (exited) when that criterion is no longer met. for each is a looping mechanism which performs an iteration a specific number of times.

exit

it

at will.

f oreach

is

The loop

is

programming because

useful in shell

once for each of a

tions

set

performs a

it

of arguments. For example,

if

set

of opera-

you want

to write a

which performs the same task on every element in a directory, or for evps list, then f oreach is the loop mechanism to use for the C

script

ery process in a shell, f

foreach item commands end

oreach

has a simple syntax, as outlined below.

listof items

(

where "item"

)

will be associated with each

element

each loop pass (or cycle). Within the loop, "item" able.

For example, consider the loop for the

"onsince csh" .

looks

at all the

users in a

currently working on the local host. If so, current status.

The

script is

is

"listof items"

in

"onsince csh,"

script

.

and checks

list

for

referred to as a shell vari-

below.

to see if they are

"onsince csh" .

prints out their

shown below:

localhost> cat onsince. csh #! /bin/csh # a simple foreach script echo -n "Enter a list of userids please (without quotes) foreach user $< echo " finger $user fgrep "On since" end echo "

"

(lj

:

)

(

|

The the

first

item of interest in this script

echo command

feed

(i.e.,

item

1).

nately, this

command and

mechanism

after the initial

since csh, .

is

the optional '-n'

This option instructs

a carriage return) after the

ing the displayed

where

(at

echo. This

is

the user response

echo

particularly useful for hav-

on the same

requires the user to insert another

echo

argument with

to not print a line

Unfortu-

line.

echo

"

"

some-

to print a carriage return. In the script called

on-

the user inputs the userids of users he or she wants to check up

onsince csh executes finger on user. The userids are entered at the command line and read with the $< format inside the foreach item list. Notice (at item 2) that user is actually a shell variable on. For each user

which

is

name

input,

iteratively assigned a

loop. In C,

user

.

new

value from the

list

on each pass through the

would be consider a loop control variable.

C

13.6

When

a user

is

and piping

it

into

rently logged on.

currently logged on, there

is

finger output running finger

a line in the

since" in it, so if the user is logged on, fgrep "On since" will return that line

with the line "On

There are other ways

notion of f oreach. The script

is

439

Shell Script Control Structures

to

perform

if

this task, but

the user

it

is

cur-

illustrates the

executed as follows:

localhost> onsince.csh jhodges susan Enter a list of userids please (without quotes) On since Feb 1 08:01:21 on ttypl from huckleberry sfsu On since Feb 1 09:26:06 on ttyp4 from modemll.sfsu.edu :

.

f oreach

is

particularly useful for performing the

ber of items returned from a

UNIX command.

same action on

a

num-

you rename all of the files in a directory with a new extension. First you would want to list all of the files in the directory, and for each item, you want to use the mv command to rename it. You can use f oreach to perform this want

For example, suppose

that

to

task using

"ch-ext csh" .

as follows:

localhost> cat ch-ext. csh #! /bin/csh # this script changes extensions in a directory # exto - original extension # extn - new extension set exto set extn f oreach

=

$1

=

$2

item 'Is *.$exto' mv $item $item: r $extn (

(D

)

©

.

end

is defined by executing a UNIX command must be enclosed in single back quotes in order to execute, and the user should pay close attention to select backquotes instead of regular single quotes, as they look very similar on most keyboards. The balanced backquotes tell the command interpreter to evaluate the expres-

In this example, the

(at

item

1).

The

list

of items

UNIX command

sion.

The

1

two variables: ( ) "exto," which is the original extension on files, and (2) "extn." which is the new extension for the files. The Is command lists all files in the current directory which have the original extension, so these are the items which will be flagged in the f oreach. The mv com-

1.

The

:

r terminology

is

script has

part of the edit global search

modification reference." on page 168.

1

command

syntax. See Table 5.9,

"Command

440

Chapter 13 C Shell Scripts

mand operates on each new extension.

"

of these items, replacing the

.

xxx"

extension with the

13.6.3 while-end

while

is

a looping

mechanism which performs

met. Often the criterion includes what

criterion

is

which

incremented within the loop. The

dition,

mands

is

iteration as long as the entry is

while

called a counter variable

takes an expression or con-

which serves as an entry condition, and loops on the embedded comas long as the entry condition is true. The while loop is terminated

end

with an

When

statement.

the entry condition

is

control falls

false,

through to the end statement. Both the while and end statement must be on their own lines, and at the beginning of those lines. The syntax for the while loop is shown below:

while test-expression commands end (

while

loops can be used for count-control loops as in the following

"looptest csh." Count

script called

an

initial

)

.

value, and then the

means that a counter is given looping mechanism will increment and evaluate control

the counter value during each loop pass.

localhost> cat looptest. csh #! /bin/csh # a simple while script set count = set limit =

initialize

counter variable

set exit variable value

7

while $count != echo hello JBH @ count++ end (

$

limit

)

In this example, the is

used, as well as the

" !

="

ments the "count" numeric ates the

same

set

of

C

relational operator,

"count + + "

shell variable

"commands"

which means "not equal," which incre-

postfix increment operator,

by one. The

while

seven times. The script output

loop then is

straightfor-

ward.

1

.

This

is

a

and control

programming terminology which is

directed to the last

refers to the fact that

statement in the loop.

iter-

no other statements are executed

C

13.6

Shell Script Control Structures

441

localhost> looptest.csh hello JBH hello JBH hello JBH hello JBH hello JBH hello JBH hello JBH

The while loop construct hides

a potentially serious problem for the un-

suspecting programmer. If the loop

means

to exit

is

successfully entered, but there

form of intervention interrupt the job).

is

An

a

infinite

Another

is

(i.e.,

is

is

manifested. Often this

stop the job) or a

loop will not correct

ror in generating an infinite loop

not updating a

initial pass.

More important

if

is

never

than identifying

of the mechanisms for creating infinite loops, because this

be avoided, there are a few ways which,

(i.e.,

The most common ercounter which is needed to

itself.

not having a valid test criterion, so the test

successfully evaluated after the all

no

then the programmer has created an infinite loop, which will

it,

continue to execute until some form of intervention

exit the loop.

is

is

a situation to

invoked religiously, will virtually

guarantee against the possibility of an infinite loop. •

Always

looping variables before entering a loop.

initialize

initialized, then there is a possibility that

have deleterious

it

will take

If a variable is

effects.

•

Always increment counter variables within the loop body. The body series of expressions which are executed repeatedly.

•

Test the loop per, to

In addition, test the

make it is

not

on a value which can

test

is

that

condition with the expected entry and exit values, on pa-

sure that they will

work before executing

always a good idea when learning

the loop.

how

to write loops to

loop with an expression which will allow the programmer to exit the

loop without killing the associated process. This expression could be a branch statement such as described in the next section.

13.6.4

Goto

The goto construct is used to switch the flow of execution to a different statement. The goto is generally used with a conditional operator to exit from a loop without explicit reference to the loop's own exit condition. The syntax for the

1

.

goto

statement follows.

Usually called an exit criterion, which

expression.

is

the logical

complement of

the entry condition or test

442

Chapter 13 C Shell Scripts

goto label

label commands where "label" can be any string. When the goto is encountered, control jumps to "label" and the commands below "label" are executed. Consider an example script called "simplegoto csh," which modifies .

loop test csh .

to exit after 3 iterations:

localhost> cat simplegoto. csh #! /bin/csh # a simple while-goto script set count set limit

= =

counter initialization 10

while ($count != $limit) echo hello JBH @ count++ if (Scount == 3) goto foo end foo

:

foo

is the label control is shifted to here

-«

Is

Executing the script does the obvious.

localhost> simplegoto. csh hello JBH hello JBH hello JBH MH-Stuff AKCL AKCL- MANUAL - PS MX-TESTS Archive-TEX Mail Code Misc News Documents F90 OracleProject TeX3 LATEX-TESTS .

Texinputs Texmacros UnixManual akcl bin dvi2ps f ilterf ile

In the last section,

it

was mentioned

loops might want to insert a graceful exit from a loop.

latex lib mail -elsewhere manpages temp tmac

that a

goto/ label

The above

programmer learning

to use

statement which would allow a

script is modified,

below, to show one

13.6

way it.

this

C

Shell Script Control Structures

could be done. The other difference

so that an infinite loop

is

is

that this script has

generated which the

goto

443

an error in

will catch.

localhost> cat badgoto.csh #! /bin/csh # a simple while-goto script with a costly error # embedded in it set count set limit

=

11

=

10

bad counter value

while ($count != $limit) echo hello JBH @ count++ echo "counter is: $count" echo echo -n "Is it alright to continue? "

set test $< if ($test != "y" endif

(y/n)

" :

=

end stop

test exit )

block

goto stop

—

control

is

shifted to here

Is

This script illustrates a previously unmentioned means of creating an nite loop: a

poor choice of counter

which exceeds the an

exit.

The

test

limit variable will allow the loop to begin, but doesn't allow

sequence inserted allows the programmer

the counter variable

while executing

infi-

initialization values. In this case, a value

and

to exit

"badwhile csh." .

localhost> badwhile. csh hello JBH count is: 12 is it alright to continue (y/n) hello JBH count is: 13 Is it alright to continue (y/n) hello JBH count is: 14 Is it alright to continue (y/n) y count is: 15 Is it alright to continue (y/n) n AKCL MH-Stuff Texinputs AKCL -MANUAL -PS MX-TESTS Texmacros Archive-TEX Mail UnixManual Code Misc akcl Documents News bin F90 OracleProject dvi2ps LATEX-TESTS TeX3.0 filterfile

to

view the value of

without outside assistance, as shown below

:

:

latex lib mail -elsewhere manpages temp tmac

444

C

Chapter 13

Shell Scripts

As you can

was allowed to cycle several times, to illustrate was incrementing properly, but that the exit test was not succeeding and wasn't going to. At that point, the script was instructed see, the script

that the counter variable value

to exit the loop.

13.6.5 switch

and case

Often a programmer will encounter a situation

made

more than two possibilities can employ nested if -then- else and case construct. but

The switch construct bilities

is

used to

in

which

constructs, or one can use the

test a pattern against a

and to redirect execution based on the value of the

for the switch statement

switch test-string case patternl: commands breaksw case pat tern2 commands breaksw (

is

shown on

must be one

a decision

exist for branching. In such cases,

switch

number of possiThe syntax

pattern.

the next page.

)

default: commands

breaksw endsw where "default"

is

used as an "otherwise" clause. The

evaluated and compared to

of the values, then control then evaluated.

When

switched to the

first

match, then the

switch ered, since

the

is

it is

"patternl," "pattern2," is

"test-string" etc. If

shifted to the associated set of

execution reaches the

"breaksw"

statement following "endsw."

"default" commands

If

it

is

matches one

commands

that are

statement, control

is

none of the case patterns

are executed.

used when a number of different possibilities must be consideasier to

program than many if -else sequences. Consider script below, which decides what to do based on

"simpleswitch csh"

what type of input

.

it

gets.

13.6

C

445

Shell Script Control Structures

localhost> cat simpleswitch.csh # /bin/csh # A simple switch and case script !

switch ($1) case dog: echo The lazy brown dog crawls under the rickety fence breaksw case cat echo The spunky cat plays with catnip breaksw case fish: echo The slippery fish swims all day breaksw default echo "The lazy typist cannot think of anything" breaksw endsw

Several points should be script doesn't

do much. Second, the

diately following all in

made with

it.

test variable

must have a colon

(

:

)

imme-

Third, there must be a default case to catch errors (a catch-

the event that cases are left out of the options). Like the other control

structures,

switch

and

ning of their respective following output

when

endsw

lines.

must be on separate

lines,

The simpleswitch. csh

executed:

localhost> simpleswitch.csh dog The lazy brown dog crawls under the rickety fence localhost> simpleswitch.csh fish The slippery fish swims all day

.

respect to this example. First, the

and

script

at the

begin-

produces the

446

Chapter 13 C Shell Scripts

and Sample Quiz Questions

13.7 Exercises

13.7.1 Exercises Exercise

1

C

Write a

cat Exercise 2

does the following.

shell script that

command

ments on the

line,

each of which

copy the contents of the

to

C

Write a

first

It

a

is

two onto

accepts three argu-

name, and

file

documents programs using

shell script that

uses

it

the third.

man

format.

It

prompts the user for the information associated with standard manual headings, and

it

uses an editor to have the user write the text associated

with the heading.

When

but to

Exercise 3

and including

C

Write a ercise 2.

13.7.2 Problem

may seem

very complicated,

you have understood

the material up

this chapter.

program document written

in

Ex-

prompts the user for the name of the program and the direcit

is

located, and

more. Both of

using

if

shell script that reads the

which

tory in

in

It

This

file.

within your capabilities

is

it

of the headings have been completed, then

all

document

the script writes the

Chapter

displays the appropriate manual page

it

these questions are associated with the material

6.

Sample Quiz Questions 1

How

are variables identified in

valid

C

shell variable.

C

Give an example of a

shell scripts?

Given an example of a

C shell

variable

you have

seen used in this manual.

Problem 2 Problem 3

What

steps

Suppose

must be taken

that

you

at

the script.

Suppose

that

ond argument with

How

list

are about to write a

What

guments

and

"

C

shell script that will take

one variable, "pathname,

set

is

.tex.

would you

"

two "

in

the concatenation of the sec-

How

would you assign the command-line

refer to the first

script?

C

shell script that will take a user

of machine names which

eleven.

a shell script executable?

"pathname"

argument from within the

You

line

the suffix

variable in the script?

Problem 4

make

are about to write a

command

arguments

the

to

are the considerations for deciding

into the script,

name and

will vary but will never be smaller than

and how

how

to input these ar-

are they assigned

and referenced

within the script?

Problem

5

What

are the differences

between

scripts for the following constructs.

C

shell scripts

You can answer

ing the next chapter. •

Variable assignment

•

Numeric variable increments

•

Reading arguments interactively

and Bourne this after

shell

review-

13.7 Exercises

Problem 6

Write a

C

shell

segment

execute an input

and Sample Quiz Questions

that uses the 'whi le' syntax

command

n times, where the

ments, and the number of times to execute the

Problem 7

Write a

mand

C shell

line

than

Problem 8

1

command,

script that takes a directory path

directory path given, finds and prints

Megabyte

to a file

all files

and semantics

command and

and a

arguments and recursively descends the

file

44

file

its

#

to

argu-

are input

type as

com-

system from the

of file type or size greater

named "large-files

.

how to write a C shell segment that asks the user to among two choices on a fast food menu, each of which has a different number that will be printed and some way to identify the item. Write or describe

select

The

script will read the response,

the response

by

sume 8%), and

itself

print the result

cents" where RESULT numbers

to

increment the value associated with

multiplied by California sales tax (you can as-

is

the

"your total comes to RESULT amount in pennies. You cannot use real

increment variable values with the @ operator.

Bourne Shell Scripts

14.1

Introduction and The

Scope

C shell and Bourne shell are both command Each environment has its own programming language that can be write scripts which are executable in its environment. This chapter pre-

last

chapter mentioned that the

interpreters.

used to

sents the

programming language associated with

the

Bourne

shell.

We address

similar issues as to those that were presented in the last chapter but apply to the syntax

and semantics of the Bourne

shell.

The following

them

topics are cov-

ered in this chapter: Invoking a Bourne shell script Shell variables Shell arguments Shell creation Shell control structures Script functions and subscripts

When you the notion of

have completed this chapter, you should be comfortable with Bourne shell scripts: how they differ from C shell scripts, how

they are executed,

how

they are created,

variables are defined and accessed, tions,

and how

write simple

Chl4

to

perform

Bourne

how

how to

they are

made

executable,

how

perform different kinds of opera-

Like the C shell, you should be able to which execute simple UNIX command se-

iteration.

shell scripts

sed and awk you need to see the source code for the script examchapter, you will find them in the "UNIX /Chi 4" directory.

quences, and you should be able to incorporate the use of the utilities in

ples in this

your

scripts. If

449

450

Chapter 14 Bourne Shell Scripts

To

C shell scripts and Bourne shell scripts, many of the examples provided in this chapter will be the same ones implemented in Chapter 13 on C shell scripts. Pay close attention to help clarify the similarities and differences between

the differences, as they can slip

When you it

forget.

Bourne Shell Script

14.2 Invoking a which

you up when you

write a shell script,

was

written. In

cial characters

on the

it

must be executed

in the shell

environment for

Chapter 13 we introduced the notion of the (#

first line

of a script.

When

the

command

!

)

spe-

interpreter sees

it expects the next characters to identify what shell environment to execute the following script in. In the C shell, the path following # would be "/bin/csh." In the Bourne shell, that path is "/bin/sh," and the first lines of the script would appear as follows:

these characters,

!

1

#! #

/bin/sh This is a bourrne shell script

You can also invoke a Bourne shell script at the command line. Of course, if you are currently executing commands in a Bourne shell this is obvious. But if you are currently executing commands in a C shell, you could tell the shell to execute the following commands in the Bourne shell. To know what to do, you must be able to recognize the prompt that signifies one shell from another. The prompt that is used by your computer system often indicate which shell is operating. Almost always the default prompt for the Bourne shell is a dollar sign, $. If you modify your login shell prompt, as you were shown how to do in Chapter 5, then you should make sure that you can still recognize the difference between different shells. Suppose that you are normally working in the C shell and want to execute a set of commands in the Bourne shell. You would invoke the shell with the

.....

/bxn/sh command,

-

This

command

The

process of creating a subshell

is

will create a subshell in is

is

shell

which

will execute all

This

is

a Bourne

"command"

which the commands parent

shell.

completed, control returns to the parent

exit the shell.

initiates

she n on

commands

in the

new

shell

When

the command exYou can also fork a

shell.

new environment

until

done as follows.

systems, your default path will prohahly include the "bin" directory.

path to be explicit.

will be executed.

called forking a shell, and the

a child process of the current shell or

new

On most

as follows:

—

ecution

I

sh command

I

am

including the

you

14.3

Bourne Shell Variables

451

/bin/sh When

this

command

return to the

is

issued, the dot-file

parent or calling

shell,

type a

may have used the mechanism of forking which sends everything typed to a file.

When done

. The

14.3

default

.profile"

shells with the

will

script

name

session,

"script" command, on standard output

one must exit the

for the session

is

To You

be executed.

to exit the shell.

to standard input or displayed

with the file

"

shell with

"typescript."

Bourne Shell Variables Besides being a

command

interpreter, the shell is also a high level

program-

ming language. The language includes variables and control structures much like any programming language. We will first look at variables, how they are declared, how they are assigned values, and how they are used. One of the most important notions of a shell script

is

As

the shell variable.

in

any program, the

arguments which are provided by the user, and the values used within the

script

must be associated with variables which can be addressed and manipulated by the user.

The Bourne

shell

variable types, as does the

may

they

may be

does not distinguish between string and numeric

C

shell.

Variables can be defined within the shell,

be defined automatically as shell

command

line

arguments, or they

defined globally as environment variables. Bourne shell variables can

also be exported to the calling environment. In the

Bourne

shell, variables are

assigned by following the variable

name

with an equals sign and then the the value, without spaces:

f

ilen=Unix-Man. tex

Note

that the syntax

does not allow spaces between the variable name,

"f ilen," the assignment character, =, and the variable value,

tex." Variables the variable

in the

name with

Bourne

shell

"Unix-man.

-

environments are referenced by preceding

a dollar sign, $, as in the

able f ilen has been defined and can

C

shell.

now be echoed

For example, the or displayed.

vari-

452

Chapter 14 Bourne Shell Scripts

localhost> echo $filen Unix-Man. tex localhost> tail $filen % \ appendix { answt oexs % \ inc lude { answtoexs % \ appendix { \ latex Examples} %\ inc lude {LatexExamples} %\printindex %\bibliographystyle{apalike} %\bibliography{unixmanual} % \ end { document

Numeric Variables

14.3.1

The Bourne

numeric and non-numeric variable similarly. So any which must be manipulated must be considered an expression which should be evaluated. The expr command can be used in either shell environment, but because the Bourne shell doesn't have a specific mechshell treats

numeric variable

anism for numeric variable evaluation syntax for using

expr

is

often used in the Bourne shell.

it is

The

shown below, along with an example.

expr argument* where "argument*" means pending on the to

work on

member to erator,

Below

task,

string

expr

that zero or

more arguments can be used, de-

evaluates each argument separately, and

is

defined

comparisons as well as numeric and logical operators. Re-

leave no space between the shell variable name, the assignment op-

and the expression. See the man page for more information on its use. is an example of incrementing a numeric variable for a Bourne shell

script:

myvar=3 myvar= expr $myvar '

+

1

where the

entire expression

is

backquoted

to

inform the Bourne shell to evalu-

ate the expression.

14.4

Bourne Shell Arguments Like the

C

the shell

prompt or interactively within the

guments

is

shell.

Bourne

shell shell scripts

identical to the

C

shell, but will

can get their input from the user shell.

The use of command-line

at

ar-

be repeated here for completeness.

14.4

14.4.1

Bourne Shell Arguments

453

Command-Line Arguments

When a script is invoked with

arguments on the

command line it appears as

fol-

lows:

script_name [args] where "args" are the required arguments of the script. Internally, the userprovided arguments are ordered by their appearance at the command line, and referenced with a dollar sign ($) and their ordinal position. For example, sup-

pose

we

rewrite the script called

searches a

file

phones csh .

named "addresses"

number. Simple enough. The

script

for a

for the

shell,

which

returns the

phone

Bourne

"name" and

keeps track of the variable by calling

name

$1: -._-. „ ONLY difference with C shell

localhost> cat phones. sh **#look up a name in a phone directory ,

.

,

fgrep $1 $HOME/addresses

The "addresses"

file,

below,

is

unchanged from

the previous example:

localhost> more addresses

USHGA: P.O. Box 8300 Colorado Springs, CO 80933 (719) 632-8300 APA: 25 Goller Place Staten Island, NY 10314 (718) 698-5738

When the script is executed at the command line, the user provides name argument, such as "APA," which is defined within the script as $1: localhost> phones. sh APA APA: 25 Goller Place Staten Island, NY 10314

(718)

the

698-5738

where the script has been executed with the argument APA, and the result of fgrep on this value, in the file addresses, is shown. In this script, there is only one occurance of APA.

them

all in

order.

Had

there been others,

fgrep would have

listed

454

Chapter 14 Bourne Shell Scripts

14.4.2

Prompting the User for Arguments

A script might

also obtain information

from the user by prompting

The most prevalent instance where one uses interrogated input is when you do not want to remember the number of arguments or their order, or when you are for

it.

writing the script but others will be the predominant users. In such cases, the

user assigns a variable

name with

the

command read, and the

variable value from the standard input. is

A simple example

script takes the

of this type of input

shown below.

echo "Enter the person's name:" read answer

Now consider a modified version of phonesp

.

csh, called "phonesp sh," .

which prompts the user for the director}' and name of the the addresses file, and for the name to look up. The response typed by the user is assigned to the shell variable

"answer"

as

shown below

for the variables "dir,"

"ad-

dress." and "name:" localhost> cat phonesp. sh #! /bin/sh # look up a name in a phone directoryecho read echo read echo read

what is the directory path for the addresses file? dir what is the name of the address file? address what is the name to look up? name

fgrep $name $dir/$address

and a sample usage of the

script:

localhost> phonesp. sh what is the directory path for the addresses file: /usr/f 1/ jhodges what is the name of the address file: addresses echo what is the name to look up: USHGA USHGA: P.O. Box 8300 Colorado Springs, CO 80933 (719) 632-8300

where

the bolded items are those entered at the keyboard.

able can be Its

made

use follows.

A

Bourne

available to other shells and scripts with the use of

shell vari-

export.

14.5

Bourne Shell Creation

455

export filename

f

ilename=$l

14.5

Bourne Shell Creation There are two steps tested.

in writing

any

script. First, the script

has to be written and

Second, the script has to be made executable. Depending on

be using the

script, this latter step

may

require

you

who

will

to place the script into a di-

which you make public, as for linking. A script is created with an editor like any other program. In the following example, the vi editor will be used, but it doesn't matter which editor is used. What does matter is that you write scripts which are clear and readable, rectory in your execution path or into a directory

you should when you write other programs. For example, invoke an edlines below into a new file. Save the file as "hel loyou sh." This example will demonstrate how the read command is used to assign variables from the standard input.

just as itor

and type the

.

localhost> vi helloyou.sh #!/bin/sh # This simple script tests user input echo Please enter your name: read name echo Hello $name

"helloyou.sh"

;

[New file]

6

lines,

106 characters

456

Chapter 14 Bourne Shell Scripts

Two

items of note in this

path to the shell environment

comment

the

As

character.

tion of the script in the script to

be executed

when you have that

it

is

are the first

file

that the only initial difference

two

(i.e.,

created the

before, #

!

sh (Bourne file

shell

/bin/sh). Also, is

a special

environment following

in the

lines,

between the Bourne

shell)

it,

the

because they indicate

and the

pound

comman so the

shell is the is still

that forces execu-

first line

forces the

environment. As with the

you will want the same way:

for the shell script,

executable, and you will do so in

C

sign (#)

to

C shell,

make

sure

localhost> Is -1 hell* -rwxr-xr-x 1 jhodges 64 Aug 25 23:54 helloyou.csh -rw-r— r— 1 jhodges 59 Feb 1 11:26 helloyou.sh

Note the use of the asterisk wildcard to list out any file starting with "hell." This way I get both the C shell version and the Bourne shell version. Note that "helloyou csh" is executable but that "helloyou. sh" is not. .

So

the next thing

executable.

Use

"helloyou

.

you must do, before you can

the

chmod command

test the script, is to

to give yourself execute

make

the file

permission for

sh:"

localhost> chmod 755 helloyou.sh localhost> !ls -1 hell* Is -1 hell* -rwxr-xr-x 1 jhodges 64 Aug 2 5 23:54 helloyou.csh -rwxr-xr-x 1 jhodges 59 Feb 1 11:26 helloyou.sh

which

retains the earlier permissions, but also gives you,

and others, execute

permissions. Note the difference in permissions between the two scripts.

execute the script

in the

Bourne

Now

shell:

localhost> helloyou.sh Please enter your name: jack Hello jack! localhost>

This example peforms exactly the same function as did

and does so so

that the difference

demonstrated.

As

before, this

between the

example

is

helloyou csh,

two environments can be

.

easily

presented to illustrate the use of

prompted variable assignment and variable reference. Once the script is running properly, you will want to name it something memorable and move it into your default execution path. Normally, users put their executables. whether hi-

14.6

457

Bourne Shell Control Structures

nary or not. in the directory "-/bin:"

localhost> mv helloyou.sh -/bin; Is -/bin/hell* -rwxr-xr-x 1 jhodges 64 Aug 2 5 23:54 helloyou.csh -mxr-xr-x 1 jhodges 59 Feb 1 11:26 helloyou.sh

mode change

In future examples, the

you move a

file

from one directory

path, the shell will not

know

that the file is

the pointers to the default path

will

now

by invoking

When

be assumed for brevity.

to a directory in

your default execution

You can reset command line.

in that directory.

rehash

at the

localhost> rehash

You can now type the rehash command works

14.6

script file

the

same

name

directly at the

for both the

C

shell

command

line.

and the Bourne

The

shell.

Bourne Shell Control Structures We now turn to the trol

means

important topic of flow control

to control

which

in shell scripts.

UNIX expressions are executed,

Flow con-

and when.

A con-

programming mechanism or construct for conditionally executing a set of expressions. The essence is to provide a test criterion, as in sed and awk. and one or more actions to be taken as a result of matching or not matching. The use of the common Bourne shell control structures will be illustrol structure

is

a

trated here. •

if-then-else-fi

•

for-in-done

•

while-do-done

•

until-do-done

•

case-esac

14.6.1 if-then-else-fi

if- then -else construct

in the

A test-expression

given, and.

is

Bourne

shell is similar to that in the

C

shell.

"then -commands" fol"else-commands" following

if true,

the

then are executed. If not. then the else are executed. The structure is terminated with an f i statement instead of an endif as for the C shell. The syntax for the if -then-else construct lowing

follows.

458

if

Chapter 14 Bourne Shell Scripts

[

test-expression

]

then then- commands else else -commands fi

Two C

test-commands)

C

made regarding Bourne shell syntax as compared to if -then-else construct. First, the conditional (i.e.. bounded by square brackets ). Remember that, in the

notes should be

shell syntax for the is

( [

]

was bounded by parentheses. Second, the construct is closed by a mandator)' f i that matches the if The else clause is not necesshell, the conditional

.

sary unless the alternate path statements ed,

if -then-else-f i

any

constructs can be

of Bourne shell commands. Consider a simple example,

list

pleif

else- commands) are includnested. "Commands" here means

(i.e.,

.

"sim-

sh," which considers two shell arguments and makes a simple deci-

sion based on their values.

localhost> cat simpleif.sh #!/bin/sh # a simple if-then-else script if

[

"$1"

=

"5"

]

then du $2 else Is $2 fi

at the command line. If the command (du) is executed on

This script takes two arguments

ment's value argument.

is 5,

then a disk usage

If the first

argument's value

is

not 5. then a listing

is

second argument. The logical equivalence relational operator shell

==

operator)

tween the equality ed below of

all

is

test

used to

test the pattern.

operator for

C

shell

Since there

and Bourne

is

first

argu-

the second

executed on the (=. unlike the

C

a difference be-

shell, a table is present-

the logical operators for the Bourne shell.

Bourne Shell Control Structures

14.6

Table 14.1: Relational operators

in

the Bourne shell

x -It y

=>

returns

1

if

x

is

less

than y

x -le y

=>

returns

1

if

x

is

less

than or equal to y

x -eq y

=>

returns

1

if

x

is

equal

x

=>

returns

1

if

x

is

equal to y and both (x, y) are strings

x -ne y

=>

returns

1

if

x

is

not equal to y and both (x, y) are numbers

x

=>

returns

1

if

x

is

not equal to y and both (x, y) are strings

x -gt y

=>

returns

1

if

x

is

greater than or equal to y

x -ge y

=>

returns

1

if

x

is

greater than

A -a B

=>

returns

1

if

expression

a and expression B

A -o B

=>

returns

1

if

expression

A or expression B

=

!=

y

y

Table 14.2: File system logical tests

in

to y

and both (x, y) are numbers

y

is

are true

true

(i.e.,

(i.e.,

return 1)

return 1)

the Bourne shell

-r FILE

=>

returns

1

if

the file

named file

is

readable by the user

-w FILE

=>

returns

1

if

the file

named file

is

writable by the user

-x FILE

=>

returns

1

if

the file

named file

is

executable by the user

-e FILE

=>

returns

1

if

the file

named file

exists

-f FILE

=>

returns

1

if

the file

named file

exists

and

is

a regular

-d FILE

=>

returns

1

if

the file

named file

exists

and

is

a directory

Note

that the shell variable $

above. This the

C

shell,

is

how

the

459

Bourne

1

is

quoted

file

in the conditional

shell evaluates expressions.

of the example

Remember

that, in

expressions evaluated by the shell had to be placed in single back-

quotes. After the script has been

made

executable,

it

can be tested as follows.

460

Chapter 14 Bourne Shell Scripts

localhost> simpleif.sh 5 Texmacros 371 Texmacros localhost> simpleif.sh Texmacros aaai.sty diss. doc footmpl alpha4.bst diss. sty jack. sty apalike.bst dissl2.doc mitthesis sty apalike.sty dissl2.sty sf suletter sty cite.bst disstitle.doc sfsuseal.ps cite. sty disstitle. sty sf suthesis sty csuletter sty doublespace. sty texinfo.tex csuseal.ps foo tmplrg diss.bst footmp tmplrgl

tmplrg2endif tmplrg3 uclaletter sty ucseal.ps ucthesis.sty

.

.

.

.

.

The student should modify ical logical operators are

this

example, as an exercise, so that the numer-

used for comparison instead of the string operators.

The types of tests which can be performed

in the

are not related to simple variable and value tests. in the operating

Bourne

shell conditional

One can refer to

status of files

number and values input arguments, show some of the available options.

system, or even to the

within the script. Tables 14.2 and 14.3

Table 14.3: Standard variables $0

=>

calling function

$N

=>

Nth command

$*

=>

all

the

in

the Bourne shell

name

line

command

argument value

line

arguments

(if

quoted, quotes

all

the arguments in one string)

$@

=>

all

the

command

line

arguments

(if

quoted, quotes

each argument individually)

number of command

arguments

$#

=>

the

$$

=>

process number (PID) of the current process

$!

=>

process number (PID) of the

$?

=>

exit status of the last task

line

last

background process

14.6

Bourne Shell Control Structures

461

14.6.2 for-in-done

As with loop

is

some

the

C

exit condition

ten in

Bourne

shell, the

Bourne

shell

is

matched,

many

The C

it

is

used of-

set of operations once

performs a

shell equivalent is f oreach. Since, in

cases, the set of arguments can be the result of a directory listing, or the

items in a process status

for

for is a looping mechanism which

programming, because

for each of a set of arguments.

As a reminder, a commands repeatedly until

shell has looping constructs.

an expression which performs a number of

listing, etc.,

for

can be a very powerful mechanism.

has a simple syntax, as outlined below.

for index in listofitems commands done The "index" here defines

index (i.e.,

ed.

the

is

assigned the

command

Then index

loop

is

is

first

a local variable called a loop control variable.

element of the

sequence which

is

list

as a value

repeated, here

"commands")

assigned the second element of the

executed again, and so on. The "in"

loop. Also note that the closing statement

is

is

and the loop body

list

is

execut-

and the body of the

component of the

a required

"done," whereas

in f

for

oreach

it

was "end." localhost> cat onsince2.sh #! /bin/sh # a simple for script users= 'hodges hodges hodges for user in $users do finger $user fgrep "On since" |

done

It

should be noted that the single quote on the users

as easily be a double quote, as long as the

pression.

The

script is

programmer

executed below.

localhost> onsince2.sh On since Aug 6 07:51:05 on console 10 days Idle Time On since Aug 6 07:51:05 on console 10 days Idle Time On since Aug 6 07:51:05 on console 10 days Idle Time

list,

is

above, could just

consistent in the ex-

462

Chapter 14 Bourne Shell Scripts

One can

also write a

for

loop without a

list

such

as:

for index do commands done In this case, the

example of

the

list is

for

assumed

to

be the

command

presented in Chapter 13, rewritten for the Bourne at all the

users in a

list

and checks

onsince. sh

local host. If so,

line

shell,

As an

arguments.

"onsince csh" onsince sh looks

loop, consider the loop for the script

to see if they are currently

.

.

working on the

prints out their current status.

The

script is

shown below. localhost> cat onsince. sh #!/bin/sh # a simple for script for user do finger $user

|

fgrep "On since"

done

In this script, the user inputs the userids of users he or she

wants to check

the script is invoked. For each user name input, onsince sh fingers the user. When a user is currently logged on, there is a line in the finger output with the line "On since" in it, so if the user is logged on, running finger and piping it into fgrep will tell. The script is executed as fol-

up on when

.

lows:

localhost> onsince. sh jhodges csalmon On since Feb 1 08:01:21 on ttypl from huckleberry sfsu On since Feb 1 12:26:08 on ttyp4 from oad-8csld.sfsu.edu .

14.6.3 while-do-done

while

is

Bourne

a second

shell

looping mechanism which takes an expres-

embedThe while loop is semantithe while loop in the C shell. The only differences are the )around the entry condition, as for the if -then- el se-

sion or condition which serves as an entry condition, and loops on the

ded commands

while the entry condition

cally identical to

square brackets

1

.

There

taster tor

is

no particular need for

(

[

true.

]

fgrep here. Any of the grep or egrep.

simple string searches than

is

grep family would work, but

fgrep

is

14.6

f i construct, and the

The Bourne is

"done" which

terminated

for

loop.

while execution loop is described with a do clause, and it with a done statement. The while, do, and done statements

while

own

loop

is

lines,

and

shown on

entry-test-expression while do commands done [

whi le

closes the construct, like the

463

shell

should be on their for the

Bourne Shell Control Structures

at the

beginning of those

lines.

The syntax

the next page:

]

loops can be used for counting events, often called count-control

loops, as in the following script called

"looptest

.

sh."

localhost> cat looptest. sh #! /bin/sh # a simple while script count=o limit =7

while

[

-«

initialize

-•

set exit variable value

"$count"

"$limit"

!=

counter variable

]

do

echo hello JBH count= expr $count ,

+

l

v

done ="

C

which means "not equal," is used because variables are being referenced. As in previous Bourne shell scripts, the use of shell variables in the test condition must be double quoted, and the variIn this example, the

"

!

operator,

able assignment spacing must be paid attention to throughout. als,

ent. In the

by the

Of course,

liter-

such as numbers, need not be quoted, but the logical operators are differ-

Bourne

shell, the

incrementing of numeric arguments

explicitly evaluating an expression with

expr

.

In the

do

is

performed

part of the loop

expression must be backquoted. Other than these differences, the

script is very similar to

localhost> looptest sh hello JBH hello JBH hello JBH hello JBH hello JBH hello JBH hello JBH

expr.

looptest csh. The .

script output is obvious.

464

Chapter 14 Bourne Shell Scripts

14.6.4 until-do-done shell looping construct is the until loop. There is no synbetween the while and until loops, and the only semantic difference between while and until is the test condition. In the former, the

The

final

Bourne

tactic difference

loop is

is

executed as long as the condition

executed until the condition

is satisfied,

is satisfied.

while in the

loop

latter the

The syntax of the until loop

is

as

follows.

until exit-test-expression do commands done [

]

To demonstrate the use of until in a script, we looptest sh to work with until ("untiltest sh"): .

will

modify

.

localhost> cat untiltest. sh #! /bin/sh # a simple until script count=0 limit=7 exit condition is the

until "$ count" = "$limit" do echo hello JBH count= expr $count + l done [

logical

]

complement

of while entry condition

v

'

which executes predictably:

localhost> untiltest. sh hello JBH hello JBH hello JBH hello JBH hello JBH hello JBH hello JBH

14.6.5 case-esac

case construct is the analog to the C A case takes a "test-string" and matches

The Bourne struct.

shell

"patterns."

it

If

one of the patterns matches the

shell

switch

against a

con-

number of

string, then the associated

Bourne Shell Control Structures

14.6

commands

are executed until a double semicolon

syntax for the

test-string case patternl) commands [

case command

is

( ;

;

)

465

encountered. The

is

shown below.

in

]

# /

pattern2 commands

commands 1

esac The

"in" is again

used (similar to the for construct) and

is

again required.

Also, each pattern must be terminated with a closing parenthesis

case is closed case patterns can

the

the patterns. * in the

list,

with esac. Unlike the patterns in the

matches any

string, so * will frequently

doesn't match any of the other patterns, script illustrating basic use of the .

shell

)

).

Finally,

switch,

the

include wildcards. For example, a * can be used as one of

as a default/otherwise case (which

case sh"

C

(

it

is

be the

required). If

will definitely

Bourne

"simple-

case $1 in dog)

echo The lazy brown dog crawls under the rickety fence

echo The slippery fish swims all day *)

echo "No item of that type in case list"

A simple

*.

localhost> cat simplecase. sh /bin/sh # A simple case script

fish)

test-string

shown

shell case is

#!

echo The spunky cat plays with catnip

used

match the

below:

cat)

last pattern

in

466

Chapter 14 Bourne Shell Scripts

The execution of this

script is straightforward.

depending on which item the item doesn't

ment

is

is

echos

input,

match any of those

The user inputs an item and,

a string associated with that item. If

in the case

list,

then an amorphous state-

printed:

localhost> simplecase.sh dog The lazy brown dog crawls under the rickety fence localhost> simplecase.sh fish The slippery fish swims all day localhost> simplecase.sh octopus No item of that type in case list

and Sample Quiz Questions

14.7 Exercises

14.7.1 Exercises Exercise

1

Write a simple shell to

script.

Try

to execute

your

script.

You may want

review Section 3.6.2 on access permissions.

Exercise 2

What does

Exercise 3

Project: In this project you will create a shell script to customize your programming environment. With this script, you will need to enter only one character in order to edit, compile, or run the program you are currently working on. When executed the script will present the menu of choices below and prompt the user for a single character to direct its

mean

it

fork a process?

to

execution.

Menu Table

P.4:

E

edit

C

compile

L

list

R

run

Q

quit

Enter your selection (E, C. L. R, or Q):

Each choice

will

a child process.

correspond to another script

When

sented again and a until the user

the process

new choice

chooses

quit.

is

will be

that will

be executed as

complete, the

menu

prompted

This will continue

for.

will be pre-

14.7 Exercises

14.7.2 Problem

46

and Sample Quiz Questions

f

Sample Quiz Questions 1

How

Bourne shell scripts? Given an example

are variables identified (referenced) in

Give an example of a valid Bourne

shell variable.

of a Bourne shell variable you have seen in this manual.

Problem 2

What [minimal] step must be taken to make a Bourne shell script useWhat additional consideration for general use of the script would

able?

be wise?

Problem

3

Suppose that you are about to write a Bourne shell script that will take two arguments at the command line and set one variable, "path-

name,

"

in the script.

Suppose

"pathname" is the concatenation " tex " How would you asHow would you refer to the first comthat

of the second argument with the suffix sign the variable in the script?

.

.

mand-line argument from within the script?

Problem 4

You and

are about to write a list

Bourne

shell script that will take a user

name

of machine names which will vary but will never be smaller

than eleven.

What

are the considerations for deciding

these arguments into the script, and

how

how

to input

are they assigned and refer-

enced within the script?

Problem

5

What

are the differences

between Bourne

shell scripts

C

and

shell

scripts for the following constructs:

Problem 6

•

"if conditionals

•

numeric variable increments

•

"for" looping

Write a Bourne shell segment that uses the 'while' syntax and semantics to

execute an input

command N times, where

the

command and

its

arguments, and the number of times to execute the command, are com-

mand Problem 7

line input variables.

Write a Bourne shell script that takes a directory path and a as

command

arguments and recursively descends the

line

from the directory path given, finds and size greater than

Problem

8

1

Megabyte

to a file

file

file

type

system

prints all files of file type or

named

"

large-files

" .

how to write a Bourne shell script that asks the user among two choices on a fast food menu, each of which has a different number that will be printed and some way to identify the Write or describe

to select

item.

The

script will read the response,

with the response by

itself

increment the value associated

multiplied by California sales tax (you can

assume 87c). and print the result "your total comes to RESULT cents" where RESULT is the amount in pennies. From a logical viewpoint, do you see any problems with

this script?

468 14.8

Chapter 14 Bourne Shell Scripts

Recommended Reading sed and

awk

Dougherty, D. [1990]. sed

&

awk, O'Reilly Associates, Sebastapol, CA.

UNIX Programming Kernighan, B. and Pike. R. [1984]. The Prentice Hall,

Rochkind, Marc

J.

glewood

Englewood

[1985].

Cliffs,

UNIX Programming

Advanced UNIX Programming,

Cliffs, NJ.

Environment,

NJ. Prentice Hall, En-

A

Appendix

Answers

Chapter

1

to

Sample Quiz Questions

- The Login Session Problem length => Short passwords are easier to break. familiarity =>

simplicity =>

When

Problem

Too close and remember it. Too simple

is

it

is

easier to break, too distant and

easily broken,

and too complex

the fewest users are logged on.

are logged on.

is

you cannot

hard to type.

and when the fewest disk-hogs

Mornings are good, and very

late.

Problem •

slow => baud (transmission) rates are much slwer with dialin modems.

•

reliability =>

Long telephone

lines are not

designed for high speed, high

quality data transmission. •

demand

Problem 4

A

=> too

user ID

many people is

trying to use a finite

number of ports.

associated with an account, and can be the

ferent hosts (machines) with different directories.

The

same on

directory

is

dif-

sim-

ply a location in the file system where other directories and files can

be organized.

A home

directory need not be

named

the

same

as the

user ID.

Problem 5

You somehow

entered the mail

utility.

Type

"q" to exit and return to

the shell prompt.

Problem 6 •

•

whoami => returns your login ID who am i=) returns your login ID

and some information about your cur-

rent login session.

469

4#

Appendix A Answers to Sample Quiz Questions

Problem 7 •

A prompt is the

systems character for requesting input and changes with the

type of input requested. Each

response types •

password prompt, a

password:

has

its

own prompt and

accepts specific

will see a terminal-server prompt, a login prompt,

shell

,

prompt, and perhaps a mail prompt.

13_FOGNet>,

terminal-server prompt;

prompt;

utility

prompt.

During any session, a user a

•

at that

login prompt;

login: password ,

prompt; ;sf suvaxl>, mail prompt,

shell

&.

Problem 8 •

Login ID and password.

•

No

•

The user ID can only be changed by the superuser; however, the user can change the name associated with the ID with chfn. The password can be

and yes.

changed by the user and by the superuser.

Problem 9 •

sfsuvaxl> passwd

issue the

==>

command

at the shell

prompt without

arguments • • • •

Changing password for jhodges Old password: => type your old password, to verify who you are Enter new password: => type the new password Verify: => type the new password again, to make sure you know what you typed

•

sfsuvaxl>

Problem 10

Hayes command for use with a

for "ATtention Dial

modem

Telephone number 338-1200,

to dial in remotely.

Chapter 2 - Electronic Communications Problem

1

•

Advantages:

•

SPEED: You

can receive and respond

to information

much

faster than

through other media. •

RELIABILITY: You know

•

CONVENIENCE: You

•

Disadvantages:

•

NETWORK:

•

MISUNDERSTANDINGS:

message has been sent and

the

will receive

that the recipient

it.

can do

it

without leaving your work area or even

your keyboard.

You

are at the

whims of network It

is

difficult to

reliability/unreliability.

express your ideas and

understand those of others.

Chapter 2 - Electronic Communications

•

SOLICITATION:

There

is

no easy way

to stop

4#

1

junk mail.

Problem 2 •

must know how

•

mail

•

mail

•

q. x. or

to

address the mail

=> must be able

to

invoke the application

at the shell

prompt

commands => must know how to interpret and use the commands: how to read mail, how to compose, send, and respond to mail

ex

=> you must

know how

to exit the application

Problem 3 •

The > symbol

•

The

•

Examples:

•

Mail:

MH:

which message

MH equivalent to the >

"PI. •

tells

>U

symbol

the +

is

current

is

schulz-dieterich@vax Mon Mar

1

06:18

2

19/772

.

.

1+ 03/02 93 vcscl90

«

Problem 4 •

Get new messages

•

List all

•

Respond

•

Put message

messages to

into

in

MH:

inc

your working mail folder: scan

message number

number 32

into

32

32: repl

your "Personal" mail folder:

refile

32 +Person-

al •

Exit

MH

=> There

is

no need

to exit

MH because you are not in a separate

environment.

Problem 5 •

c

•

Slash, as in

vi.

Problem 6 •

SPEED: One

can respond to a posting so rapidly that

thing you •

ANONYMITY:

would

it

is

easy to say some-

later regret.

Because you are rarely close are communicating,

it

is

to the person with

whom

you

easy to say something you might

never say openly. •

EXPRESSION: The

receiver has no

flection,

way

to

guage your expression, your

in-

your pauses, each keys to understanding what a

person means.

Problem 7

A

flame

when

is

an electronic insult or criticism. Flames are usually sent

a person

thinking,

is

when

responding

to a flame,

a person has a

something, publicly, which

is

mean

when

a person

streak, or

when

this will

acting before

a user has said

way it was said draw flames from people

both incorrect and the

shows inconsideration. Oftentimes

is

472

Appendix A Answers

Sample Quiz Questions

to

who

are knowledgeble and insulted

by the poster's ignorance.

Problem 8

•

g

newsgroupname

•

f

or

F The name address convention

Problem 9

host name, such as

is

given below. The

SFSUVAX1. The

such as SFSU. and the third term

first

second term

item

is

the local

the institution,

is

the institution-type, such as

is

EDU: HOST.INSTITUTION.INSTITUTION-TYPE

.COM .EDU

.GOV .MIL

.UUCP Country Codes (such as

Problem 10

The

CA for Canada, FR "etc/hosts,

called

file is

"

for france. etc.

which contains a

which the present host knows about. This

work communications, •

•

ENTRY #2 => ENTRY #3. .

Chapter 3 - The UNIX Problem

is

list

of hosts

used for internet-

in particular electronic mail.

ENTRY #1 => Internet Protocol (IP) Address, which is used like a telephone number

•

table

1

.

for host-to-host

Symbolic or =>

Name

File

Name

communications

address for the machine

aliases for the host

System

-name \*foobar\* -print

find

Problem 2

mkdir ~/Docs/Letters/TeX-01d; cp -r -/Docs /Letters /TeX -/Docs/Letters/TeX-Old

Problem 3 Problem 4

Is -aF

which

tells

where

to find

tionally find source

an executable and whereis

and man pages. Whereis

is

more

produce the same answer as which. Then again the

example below. The user wants

A

may

is

not.

and may Consider

know what will happen when he /usr/ucb/Mail will be execut-

major difference between which and whereis

looks for the executable that

used to addi-

to

or she types mail, and finds out that ed.

it

is

versatile

is

that the

invoked when you type what you

but the latter looks for exact references to what

you typed.

former t\

ped,

I

Chapter 4 -

•

which

File Editing

473

which mail)

(e.g.,

/usr/ucb/Mail •

whereis

(e.g., whereis mail) /bin/mail /usr/ucb/mail /usr/man/manl/mail

mail: Problem 5

cp

Problem 6

Any

.

-r dir

of the following

•

cd

•

cd

•

cd

•

cd $home

•

cd /usr/fl/vcscl999

is

acceptable:

.

.

Problem 7 %

chmod 755

*

.

tex

Problem 8 %

rm ~/subl/sub2/* dvi .

Problem 9 • • •

• •

Chapter 4 -

The following

bin => usr => dev => lib => etc =>

are illustrative of directories off root

on

system binaries local files, user directories,

device

files

system

libraries

such as

ttys,

man

pages, etc.

disk drives, printers

system commands such as chown, chmod, mount

File Editing

Problem

1

access/open/create the

file

insert/append text

move around modify

text

the file in comfortable sized

chunks

on comfortable sized chunks

perform global manipulations/modifications exit in different

ways save

the file

include other files or parts of files cutting and pasting between files

Problem 2 •

vi

•

emacs

=>

:

57 => gotoline (prompts for

line:

57)

UNIX

systems:

4 #4

Appendix A Answers

Sample Quiz Questions

to

Problem 3 •

•

vi =» zz and :q or :q!, or :wq or :wq! emacs => ,

Problem 4

zz or :wq!

Problem 5

filename

Problem 6

/beezlebub

Problem 7

(slash)

Line and screen editors. of a

A

a time.

file at

A

line editor displays

and works on one

screen editor displays blocks of a

file

and

line

may ma-

nipulate and modify blocks of text.

Problem

8

:1,$ s/coconut/pineapple/g

Problem 9 •

vi

•

emacs

=>

$

,

:

1

=> ,

tells the OS where your home directory

•

MAIL

=>

=>

tells the

tells

the

A command

Problem 9

OS who you OS where alias

are

.

.

.

result of

whoami.

It is

terward. Another

way

your mail.

to look for

to look at

it is

that the alias

commands

to easily

names, but directory paths can be collapsed

The problem

most

is

new name

basically a lookup table entry for

collapse long or often used

trols the definition

is.

allows the user to provide a

more commands.

Problem 10

system associ-

shells.

to

one or

what comes

command

is

af-

used to

remembered command

this

way

as well.

likely an incorrect terminal type, since that con-

of keyboard equivalents, \example

echo $term set term=vtl00 rehash

•

%

•

%

•

%

•

Try

vi

again. If these did not work, then

go look

in

"

/etc/termcap"

for

a potentially suitable replacement term type.

looking

ways

at stty for

manually

•

try

•

talk to a guru or a system_administrator

Problem !

!

to

set the

keyboard

characteristics.

1

:s/755/700

Problem 12

process 215, 210, 206, 217 are sleeping % kill -9 214

(a) (b)

Chapter 6 -

File

Problem

1

Problem 2

Formatting and Printing WC

counts

lines,

words, and characters.

PostScript figures can take up a

lot

be a large printing job. The easiest users

is

to print

Problem

to

trees.

3

HEADINGS:

NAME SYNOPSIS or SYNTAX DESCRIPTION

number of

may

reduce the affect on other

pages with PostScript figures one

a previewer to reduce the

mention saving

of space, and even one page

way

at a time.

print cycles

you

Always use

require, not to

Chapter 6 -

File

Formatting and Printing

477

EXAMPLES BUGS FILES •

REFERENCE FORMAT: .

TH=> SH =>

•

EX,

•

.nf, •

Multipart title Subject header

.EE=> Examples .fi=> Verbatim Examples

DISPLAY METHOD: tbl file

|

nroff -man

|

col

more

|

The file has to be formatted in manpage format. There is a special macro package (the man package) for doing this. This command takes input from the SI. Output must go through more for paging. The TBI and COL commands are OK. but I do not even know what they do yet, so do not worry about them. Problem 4 •

nrof f =>

.

is •

in +NUNIT ...

.in -NUNITS, where N

a unit of choice, inches, cm.

latex => begin {quote}

mm.

is

a

number and

units

etc

end(quote)

...

Problem 5 •

nrof f-1 => .ps +2

•

nrof f-2 => \f 2 over \fl does local

•

latex-

•

latex-2 =>

1

=>

\

Large

two

increase the point size of text by italics

increases the point size of text by

{\em over} does

steps

two

steps

local italics

Problem 6

nrof f/trof f

:

The macros ".11 item, and

" .

1" starts the

el" ends the

latex: begin {enumerate}

starts the

and end {enumerate} ends the

nrof f/trof f:

.11 1 ,1s

less student support ,1s

increased tuitions and fees .Is

lower motivation .el

list,

" .

Is" begins each

list

list, list, list.

each item

is

begun with item,

4#8

Appendix A Answers

to

Sample Quiz Questions

latex:

\begin { enumerate \item{less student support} \item{ increased tuitions and fees} \item{ lower motivation} \ end { enumerate Problem 7

It

prints the file

"

code c" on .

8 1/2" x 11

"

pages with the header "my-

file" on each page using the vgrind program. Problem 8

latex filename (assumes

filename.tex)

bibtex filename (assumes

filename. aux)

latex filename (assumes

filename.tex)

latex filename (assumes

filename.tex)

dvi2ps filename (assumes

filename. dvi)

lpr -Plaser -J BINN filename (assumes filename.ps)

A full set of passes in latex may be all of these passes, depending on what you are doing. The minimum is a latex pass, a dvi2ps pass, and maybe an lpr pass, depending on how dvi2ps is interpreted by the system Problem 9 •

nroff

.ce •

.

•

.

•

1

"Mating Habits of Computer Generated Amoebas"

nroff sc

titlel:

title2:

"Mating Habits of Computer Generated Amoebas"

nroff

title3:

su "Mating Habits of Computer Generated Amoebas"

latex title: \title{Mating Habits of Computer Generated Amoebas)

•

.

•

\

nroff

heading:

su "Introduction"

latex

1

heading:

sect ion (Introduction)

Chapter 7 - Networking

4 #9

Problem 10

nrof £

no-fill command is nf and the fill command is f i. These commands would be placed at the beginning of a new line, the first

=> The

.

.

before the text and the second after the text.

latex => The

no-fill command is begin {verbatim} and the fill command is end {verbatim}. These commands would be placed at the beginning of a new line, the first before the text and the second after the

text.

Chapter 7 - Networking Problem

1

The idea here is that you do not know what the person's userid is, so you must find that out and then you use the userid to find out what

first

the person

is

up

to.

finger foobar fgrep foobar-ID rwho -a who fgrep foobar-ID users fgrep foobar-ID rusers fgrep foobar-ID I

I

I

I

Problem 2

tar

By

is

many files and concatenate them into a single file. minimum block size is forgone, resulting in a small compress removes unused/unecessary space in a file,

used to take

so doing, the

savings in size,

and usually •

results in

50%

savings in size, depending on

create an archive => c

•

view the contents of an archive =>

•

extract an archive =>

Problem

file type.

t

x

3

ftp sumex-aim.stanford.edu (ID anonymous, the password is generally your userid and domain address)

•

login sequence =>

•

find file =>

•

change retrieve mode => binary

•

retrieve

•

exit mode => exit or bye

Problem 4

cd pub.

Is,

cd

to directory, etc.

mode => get file, mget files

Approximately 507c of the

Problem 5

tar tvf cl.

3. 1.2.

tar

(this latter

file's original size is

supports wildcards)

saved.

4u0

Appendix A Answers

to

Sample Quiz Questions

The optimal choice

Problem 6

is

to use rep, since the alternative

of telnet or rlogin, cd,

Is, tar,

compress, and

is

a combination

ftp.

rep -r fuzz cs .blowtorch. edu: /usr/lib/tex/inputs texinputs .

Problem 7

who => Fastest for login. rwho => Same for remote hosts users => Fastest for login. rusers => OK as fastest.

w =>

Most

as well.

specific for idle time and current processing.

finger => The most personal. Shows login time. last => Most specific for idle time. Not fast if machine Problem 8

has been up long.

system management refers to the organization, distribution, and

File

allocation of resources within your personal directory.

keep your directories clean and organized be organized similarly to the

names of binary on.

UNIX

file

at all times,

You should

and they should

system as a whole. That

directories inside your directory should be bin,

You should make

sure that

you

is,

the

and so

are not wasting space by eliminat-

ing unnecessary files regularly, and by archiving or at least compressing those used infrequently, du, for filesystem

Problem 9

The

listings

df tar, and compress

were produced by the df command. Filesystem

have enough

free space

directories, so

we

on any filesystem

to support the

cannot use any of those disks. The

system A, associated with the device least

are used a lot

,

management.

space (-6.5 Meg); so

it

would be

"

A does not

uncompressed

" / "

disk on

file-

/dev/raom," has

the

the least likely candidate to sup-

port the port.

Problem 10 is intermittent, one would suspect someone running a number of different people running large processed, per-

Because the problem large process, or a

haps for a class.

To check

out this theory, or any theory,

and what they are doing. This 'w'

command,

this in

since

it

is

you could see who

is

on the system

most expeditiously accomplished with the

also provides system load information.

You could

use

concert with 'finger' to find out more about the user(s) in question.

is one of responsibility. If a user knowingly slows an entire work of all its users, then someone is violating basic common sense. The machine is not their own personal toy; it is not a PC. and they should respect other user's right to do work loo. The best thing to do would

The

issue here

host and the

be to ask them to nice their jobs, so that they took a low priority ing.

Another thing they might do would be

to run then job(s)

in

process-

on an isolated

Chapter 8 - C Programming

network where

part of the this

was

their

impact and seek ways to reduce

Chapter 8 - C Programming

•

481

not adversely affect anyone. If

the problem, then the user should also be spoken to, so that they re-

alize their

Problem

work would

I

it.

I

1

syntax => The structure/order associated with symbols and expressions

which comprise

legal expressions in the language.

Examples

are

the use of parentheses to define a function, or the use of a semi-

colon to terminate an expression. •

semantics => The meaning of expressions

are the concepts associated with the def-

inition of a function

and the termination of an expression (not

the

C

is

language. ..what they are

Examples

used

Problem 2

in the

for.

symbols or how

a high-level

it

is

implemented).

programming language. The strengths of a high-level

language are that they are somewhat hardware independent (portability),

they are easier to read because they appear more like a natural lan-

guage such as English, and they are easier

to

compose

into procedural

units.

level =>

The programmer is writing expressions which will manipulate hardware components almost directly. There is almost no ab-

•

low

•

high level => The programmer writes expressions which appear more En-

straction of the expressions.

and effect many lower level operations. The actual which are performed by the hardware are abstracted so

glish-like

tasks

that the

Problem

3

programmer need not be aware of how they

are done.

Portability means that a program which is implemented in a programming language on one hardware platform can be taken in source-code

version to another platform with a similar/same compiler, recompiled,

and

it

C

a

is

will run without modifications or affect

good language

language.

It is

to learn

because

it

is

on functionality.

ANSI

a standardized version of the

not currently the most portable dialect of C, but

it

has

the potential to be.

Problem 4

Programming

style

is

important for you, the programmer,

re-reading/modifying your programs

grammers

to read/understand

any kind of

text if

your programs.

We

find

it

in

terms of

other pro-

easier to read

follows certain grammatical, organizational

,

and

The same is true for a program. The opposite is also program doesn't comply with certain conventions, it is pain-

style conventions. true; if a

it

in the future, or for

ful to read.

*\o2. Appendix A Answers

to

Sample Quiz Questions

Banner => program name,

•

file

name, author, version, purpose,

ables, implementation notes, formulas, credits for

gorithms,

local vari-

borrowed

al-

etc.

Readability => veritcal and horizontal spacing of functional segments,

•

spacing between operators and variables/arguments, location of curly braces, lining

and so

Problem 5

up of assignment statements,

forth.

There are three component blocks

in a

C program:

( 1 )

headers, (2) del-

The header block defines the interfaces between functional components. The declaration block defines variable and function types. The statement block defines the expressions carations,

that will

Problem 6

The in a

{

C

and

(3) statements.

be evaluated during execution.

and

(open and close curly braces) define a functional context

}

program. They can be used around any expression, but, accord-

ing to convention, should only be used to surround

compound (more

than one) expressions.

Problem 7

Two

which

precompiler directive, er

Problem

scanf "%d" (

,

scanf and print f. They both reside in #include where stdio h is the name of a function head-

standard functions are

the stdio library,

is

accessed with the .

file.

8

&f oo)

printf("The annual rainfall in Springfield, MA is %d inches\n" Problem 9

It is

If

well inject

A

first error,

new

you

you

will [very] often serendipidously cor-

try to correct the other errors,

you may

errors.

function prototype

is

simply a duplicate of a function's type and

header, terminated with a semicolon. first

;

often the case that one error propagates and creates other errors.

you remove the

rect other errors as well. If

Problem 10

foo)

,

A

prototype

is

placed before the

procedural component in a program as a check on the types and

order of functions and parameters. After that, the actual definition of a function can occur in any location in the portant to use function prototypes

is

place functions where they semantically

reason

is

that

fined in the

it

sets the

file in

programmer up

a library.

file.

that

it

One

reason

why

it

is

im-

allows the programmer to

make

the

most sense. Another

for later using the functions de-

Chapter 9 - C Programming

Chapter 9 - C Programming Problem

483

II

The >= and = foo =

ScSc

foo = 10 && foo = 1 && bar find Problem

-name \*.eps -print

.

3

awk

'{print $1 "/" $2 "/" $3 "/" $4 "/" $5 >" f ileout"

}

Problem 4

sed -f sedfile

*

sedfile:

s/got a fair trial/got an unfair trial/g Problem 5

Whenever

a reserved character, such as a dollar sign, a backslash, or

an asterisk

is

ceding

it

used

in a

regular expression,

it

must be escaped by pre-

with a backslash. For example, the use of an asterisk

ular expression could be

in a reg-

done as follows:

-name \*UnixProject\* -print

localhost> find

where the asterisk is escaped because the find command has a meaning for it otherwise, so you must disable that meaning.

special

Problem 6

localhost> Is -1

|

awk '$4

>

100000 {print $4, $8 >"foo"}'

Chapter 13- C Shell Programming

491

Problem 7 Ll L2

=>

spiderweb, beetlejuice}

{anthill,

Problem 8

localhost> w localhost> w

|

|

awk '$1 /[a-z]*/ {print $1 $8}' or awk '{print $1, $8}'

Chapter 13 - C Shell Programming Problem

Shell variables are identified with a leading dollar sign ($).

1

ample would be $ Instances of

C

1

,

where

1

A valid ex-

refers to the first user-provided argument.

shell variables that

we have

seen are $term and $editor.

Problem 2 •

Change

•

Put the script into a [bin] directory with other scripts

•

Otherwise add the directory where the

Problem

the permissions

on the

script so that

it

is

executable

script resides to

your search path

3

(a)

set pathname

(b)

$1

Problem 4

=

$2.tex

The number of command-line arguments is not limited to 9, but the is not sure what number of arguments will be required, so the script cannot be written to take a fixed number of arguments. The best thing to do is to somehow get a list of machines from some other process (ruptime for machines which are currently up, etc.) and input them as a single argument and then use foreach to cycle through each user

machine and evaluate

it

in

whatever way the user intends.

set user = $1 set machines = 2 foreach machine in machines

Problem •

C

5

Variable assignment: shell => uses set

Bourne •

C

shell

and spaces between variable, equals

sign,

and value

=> doesn't have to use set and no spaces between variable, equals sign, and value

Numeric variable increments: shell => use the

Bourne

@

sign to assign and increment variable values

shell => uses standard notation to assign

ment variables

and uses expr

to incre-

492

Appendix A Answers

Sample Quiz Questions

to

Reading arguments

•

C

shell => uses the

Bourne

interactively:

echo and $< notation

shell => uses the

to read

arguments

echo and read notation

to read

arguments

Problem 6 #

!

/bin/csh

set count set limit set command

=

=

$2

=

$1

while $count $ command @ count++ end (

!=

$

limit

)

Problem 7

#!

/bin/csh

set dir = $1 set ext = $2

find $dir

\(

-name \*.$2 -o -size 100

\)

-print

Problem 8

#!

/bin/csh

echo What would you like to order from the menu below?' echo Big Mac - 150' echo Enter 1 for echo Enter 2 for Fries - 125" echo set answer = $< if

(

@

$answer == price = 150

1

then

)

else @ price endif @

price

=

=

(

125

$price

+

(

(

$price

*

8

)

/

echo " echo "Your total comes to $price cents"

100

)

Chapter 14 - Bourne Shell Programming

493

Chapter 14 - Bourne Shell Programming Problem

Shell variables are identified with a leading dollar sign ($), just like

1

A valid example would be $ user-provided argument. We have not seen shell variables.

cific to the is

C

the

Bourne

shell;

because the default

shell

1

,

where

1

C

refers to the first

instances of variables speshell

we have worked with

however, the same variables, such as $term, would be

defined for the Bourne shell.

Also identical to the

Problem 2

C

shell:

•

Change

•

Put the script into a [bin] directory with other scripts.

•

Otherwise add the directory where the script resides to your search path.

Problem 3 (al) (a2)

the permissions on the script so that

Reference

the

is

same

as for the

C

it is

executable

shell:

pathname=$2 tex or set pathname=$2 tex .

.

$1

(b)

Problem 4

The number of command-line arguments is not limited to 9, but the is not sure what number of arguments will be required, so the script cannot be written to take a fixed number of arguments. The best thing to do is to somehow get a list of machines from some other prouser

cess (ruptime for machines which are currently up, etc.) and input

them

as a single

argument and then use for

chine and evaluate

it

in

to cycle through

each ma-

whatever way the user intends.

user=$l machines=$2 for machine in machines do .

.

.

done

Problem •

5

"if conditionals:

Bourne

C shell •

shell

=> uses brackets around the conditional and ends with

"fi."

=> uses parentheses around the conditional and ends with "endif."

Numeric variable increments:

Bourne

shell => uses standard notation to assign

and uses expr

ment variables

C shell

=> use the

@

sign to assign and increment variable values

to incre-

494

Appendix A Answers to Sample Quiz Questions

"for" looping:

•

Bourne

C

shell => uses "for"

shell => uses "foreach"

and "done."

and "end."

Problem 6

#!/bin/sh count=0 limit=$2 command=$l

while

[

"$count"

!=

"$limit"

]

do $ command count='expr $count

+

1'

done Problem 7

#!

/bin/sh

dir=$l ext=$2 find $dir \( -name \*.$2 -o -size 100

-print

\)

Problem 8

#!

/bin/sh

echo What would you like to order from the menu below?" echo Enter 1 for Big Mac - 150" echo echo Enter 2 for Fries - 125" echo read answer "$answer" then price=150 else price=125 if

[

=

1

]

fi

price='expr

\(

$price

+

\(

\(

$price \*

echo " echo "Your total comes to $price cents"

8

\)

/

100

\)

\)'

The

system

file

A directory

is

)

(

comprised of directories and is

a branch point

and

is

files

used to organize

files

and other direc-

tories

ROOT directory:

•

•

•

•

A file •

•

file

system

ROOT organizes all files and directories ROOT is the access point for any file or directory ROOT is not organized by any other directory )

(

The top of the

in the file

system

contains or organizes information

|

A file cannot organize any other files or directories A file is always a terminal (end) of a branch in the file

system

ROOT DIRECTORY

DIRECTORY termcap

ACCOUNT DIRECTORY

.login

495

l

Appendix C Generic Login Session Terminal Server

I

**-

"t

host," "hosts," or "bye"

i Login: vcscl234 Password: gen$u3qd

Login Script

+ USER

set

HOME

set

I execute .cshrc set

TERM,

set history, etc.

Default (C) shell

define aliases

commands

execute

I execute .login set

MAIL,

set

PATH

Login

display prompt

commands

(e.g.,

pwd,

command I

Command

exit (to terminal server)

496

Issue

Is.

cd, cp.

mv.

rm, mkdir. rmdir. etc.)

\ execute

shell

is

"logout" or "exit"

^PmMMr

Appendix D

Bare Bones UNIX

Commands

NAVIGATION •

whoami:

what

USERID

•

pwd:

what

is

•

cd DIR:

relocate

me

new

is

associated with this session?

the path to this directory? to the directory

DIR

DIRECTORIES named DIR

•

mkdir DIR:

create a

•

mv DIR

change the name of directory

•

rmdir DIR:

•

chmod

DIR2:

delete

XXX DIR:

directory

DIR

to

DIR2

empty directory DIR

DIR

change permissions on directory

to

XXX

FILES copy of FILE and name

•

cp FILE FILE 1

create a

•

mv FILE FILE2:

change the name of the

•

rm

delete the file

•

chmod

•

cat FILE:

display a

file

named FILE

(scrolls)

more FILE:

display a

file

named FILE

(pages)

•

file

FILE:

XXX FILE:

FILE:

it

FILE

1

file

FILE

to

FILE2

file

FILE

to

XXX

FILE

change permissions on

identifies file type of

FILE

ARGUMENT TYPES and

•

File

•

Example:

director}'

arguments can be explicit

OR path, as required

cp foo mynewfoo cp /usr/f2/jhodges/UNIX/MOD5/DOTFILES/host

bin

497 i

498

Appendix D

SHORTCUTS

and

WILDCARDS

•

$home:

home/login directory

•

-[userid]:

account directory path for userid (defaults to $home)

•

.:

current directory

•

..:

parent directory (one up from current)

•

*:

matches any number/kind of characters

.

Shell

prompt

f

Invoke program

f

Program

J

_L Initialize

program

"." file

Display program f

prompt

Execute

commands J

Command Program

Shell

Legal program

J

exit

command

prompt

499

ppenaix mail as a Generic Utility

ELECTRONIC MAIL (EMAIL) • A method for communicating with other computer users • A method for submitting assignments • A method for requesting assistance • A method for seeing when someone is around, when they are busy

MAILER or MAIL HANDLER A program that allows you to compose, •

send, and read email

MAIL MESSAGE •

Text that you create or compose (and

•

When someone save

it,

edit)

sends you email, you can read and respond to

and delete

it

as

you would with any

it,

file

REQUIREMENTS

500

•

you must have access

•

you must know how a mailer works

•

you must know the "address" of the user you

to a mailer

are sending mail to

mail as a Generic Utility

Shell

prompt

program

Initialize

f

mail

(^

.mailrc

J

J

w

Display program

(

prompt (&)

1

?,

#,

r,

R, ,

s,

d,

q,T)

1

f

Execute

Command x,

Shell

mail 2.

mail foo

3.

mail foo

4.

~r

6.

s

7.

#

8.

r.

FILE

FILE

< FILE

q

prompt

* READ mail * COMPOSE mail to userid foo -*-

SEND

"*"

EDIT

-*•

INCLUDE

*"

SAVE

file

FILE

to userid foo

mail message (on a blank line, insert with T, stop insert with , exit with ZZ) file FILE into mail message (on a blank line)

mail message to FILE (after reading a msg)

* READ MESSAGE number # (e.g., 3) R

*-

RESPOND to mail

message

(r replies to all recipients)

10.

• DELETE mail message number # (e.g., d3) " SEND composed mail message (or )

11.

*"

HELP (info on commands/syntax)

*

EXIT, QUIT

9.

12.

d#

x.

q

the mailer

501

i^^^H^H^ as a Generic

File Editing

A file: What you •

•

•

create or

modify when you use an editor

Contents: Data or information •

A

•

A graphics application creates and

•

An editor creates and saves text into files (i.e., the two above are editors)

word processor

Operations:

Ways

to

creates and saves

manipulate

•

Create, copy, rename, delete

•

File operations take file

documents

into files

saves figures into

files

files

names

as

arguments

Types: Text and binary •

Text

refers to

[human] readable characters and numbers

Text is coded according to a convention, called ASCII (American Standard for Coded Information Interchange) If

you can read

Any

•

readable

a

file,

then

it

is

file (text file) is

a text

refers to the text version of a

Binary

refers to a

machine readable

human

file

editable

Source

program file

readable

Binary

files are

Binary

files are not, in general, editable

not

File editing: Creation, insertion into •

and modification of

file

Requirements:

AND You must know how to use the editor, AND The file must not exist, OR The file must exist and be editable. AND

502

Utility

You must have

access to an editor,

You must have

read/write permission on the

file

content

File Editing

Shell

Utility

0U3

GD

prompt

program

Initialize

as a Generic

(

.exrc

J

r

Display program

i,

prompt (emptv

k,

buffer)

D,

a, o,

O, ESC,

w,

1,

b,

h,

j,

x, y, d,

r,

J

p, P,

:,

.,

etc.

1

r

Execute

Command ZZ,

Shell

1.

VI

2.

vi

3.

i.

FILE

—

A,

O

a.

o.

—

4.

ESC

5.

h.j, k.

1

:q, :q!,

:wq, :wq!

prompt

* -*"

INVOKE INVOKE INSERT

vi

EDITOR

vi

on FILE

characters(here, right, end of sentence,

below, above) -*~

TOGGLE

to

-*•

MOVE

cursor

command mode

(left,

6.

w. b

7.

rCh

—

yy,

yNy

MOVE

WORD: cursor (forward, backward)

*•

REPLACE

character where cursor points

BY

dd,

dNd

Ch

*•

DELETE

character under cursor

**

YANK

sometimes called (one

10.

right)

->

with

9.

BY CHARACTER;

down, up,

—

DELETE

line,

sometimes called (one

line,

COPY;

N lines) N lines)

CUT;

504

Appendix

11.

d$,D

12.

p,P

13.

:

-

—

G

DELETE

to

PASTE

below, above

GLOBAL

command :#

end of

-

go

line

to line

FILE

#

include file FILE :s - search and replace :w - write :r

:q

REPEAT

14.

-

last

(in 15.

ZZ,

EXIT

vi

-

nG

GO

cursor

quit

command command mode

only)

(some save, some don't,

some 16.

at

write to

to line n. If

end of file.

n

is

new

file)

omitted, then go to

«-——^—

Appendix H Execution Path Program/command

EXECUTION

•

Running

•

Invoking the

the

program on data

command on arguments

REQUIREMENTS

AND

•

The program must be executable.

•

The program/command must be located you are currently located. OR

in the directory in

•

The program/command must be located

in a directory in

execution path. •

FILE •

command

a path to the

SYSTEM PATH A method of organizing

and locating

files

•

Full path: Starts with the root directory.

•

Directories are separated with slashes.

Example:

your

OR

The user must provide

•

which

and directories

/

/

/usr/local/bin

EXECUTION PATH A list of directories •

•

•

When you issue a command, for the command If •

found, and

if

it

is

each directory

executable,

Example: mail and

it

is

Most commands

searched

executed

vi

these clearly do not reside in the user's they are executed nonetheless •

in the list is

home

directory, but

are in the default (already provided) path, so

is

the bin directory in each account directory. If

you

EVER

command

see the response

exists, then

you

"Command

not found"

when you know

are not using the proper path to the

the

command

505

•

Each directory and

•

There are three

•

file

can be secured by the owner.

LEVELS

of security:

YOU in your directory)

•

Owner

(permissions for the owner:

•

Group

(permissions for a specific and predefined group)

•

Other (permissions

There are three

TYPES

for

anyone

else)

of permission:

•

Read

•

Write (allows users

•

Execute (allows users

(allows users in level to read a

•

Each permission type

•

The permissions

is

modify a

in level to

or directory) file

execute a

or directory)

file

defined with a binary flag (0

is off,

•

When

1

is

on).

OCTAL

4

111100100 rwxr--r-Own

or search a directory)

are concatenated into a single 9-bit string:

4

7

in level to

file

Grp

BINARY TYPE

LEVEL

Oth

a long directory listing

command

(Is -1) is

issued, the binary permissions

are displayed. •

When

•

The execute

a

user wants to change permissions (chmod), they can use the octal code. bit

must be

ON

for a user for a

program

to

be executable by the

user.

506

1

ppendix J ASCII Characters

ASCII (American Standard Code

for Information Interchange)

standardizing character sets for use in different computers. sists

column

case

a protocol for set

con-

of the integer equivalents in the table below. For example, the blank char-

acter, represented as 'bl' in the table, is represented 3,

is

The usable

2).

'a' is

The

capital 'A'

is

with the integer '32' (row

represented with the integer '65,' and the lower

represented with the integer '97.' Because the standard alphabets,

for either case, are represented with sequential integers, the conversion

from

uppercase to lowercase (or vice versa) can be accomplished through simple addition or subtraction (e.g.,

A

= a-32,

=

a

A+

ASCII Character 1

3

2

3

bl

i

*

+

3

4

5




7

F

G

H

8

P

Q

9

Z

10

4

(

)

5

2

6

4 "

32)

Set

5

6

7

8

9

#

%

&

'

$

-

1

1

'-

6

7

8

9

@

A

B

C

D

I

J

K

L

M

N

R

s

T

U

V

W

X

Y

/

A

[

]

_

a

b

c

d

e

f

5

o

h

i

J

k

1

m

11

n

o

P

q

r

s

t

u

V

w

12

X

y

z

{

1

}

E

507

C Functions

This text has introduced the basic concepts associated with programming in

ANSI

C.

The novice programmer may wish

to extent his or her skills

by mak-

ing use of function calls which have not been discussed in the text. For that pur-

pose, the followng table available with

ANSI

is

included.

The

table presents standard functions

C, their use, their library, their argument types, and their

function tyoes. Specific implementations

may

differ in location or explicit in-

vocation.

Function

Name abs

Library

Description

Argument

Function

Types

Type

integer absolute value

math.h

int

int

acos

arc cosine

math.h

double

double

asin

arc sine

math.h

double

double

atan

arc tangent

math.h

double

double

atan2

arc tangent

math.h

double, double

double

math.h

double

double

cosine

math.h

double

double

hyperbolic cosine

math.h

double

double

math.h

double

double

math.h

double

double

math.h

double

double

v.

ceil

ceiling (lowest

number Esq

cos

whole

not less than arg)

155

cosh

^ *

exp fabs floor

exponential function (e

)

double absolute value largest

whole number not

greater than argument

508

x

C Functions

Function

Description

Name

Library

509

Argument

Function

Types

Type

natural logarithm (base-e)

math.h

double

double

base- 10 logarithm

math.h

double

double

exponentiation

math.h

double, double

double

sine

math.h

double

double

sinh

hyperbolic sine

math.h

double

double

sqrt

square root

math.h

double

double

tangent

math.h

double

double

hyperbolic tangent

math.h

double

double

stdio.h

FILE*

int

stdio.h

char

*, int.

stdio.h

char

*,

stdio.h

FILE

log ""ST"

u

login

**

pow

^

sin

6q S3 En

^

tan

tanh fclose fgets

fopen fprintf

file

close

string input file

from

file

open

text file formatted output

FILE

*

char *

RLE*

char *

*,

const char *

int

types that match

output arguments

fread

binary

file

input

stdio.h

ft.

t3

fscanf

text file input

stdio.h

void

*, size_t,

FILE

*

FILE

*. const

size_t

char

*

size_t

int

types that match input arguments En

fwrite

binary

file

output

stdio.h

void

*, size_t.

FILE

size_t

size_t

*

ft*

getc **

character input from text

stdio.h

FILE*

int

stdio.h

no arguments

int

stdio.h

char

char *

file

getchar

character input from

keyboard gets

(stdin)

string input

keyboard

from

(stdin)

*, int

51

Appendix K

Function

printf

Argument

Function

Types

Type

Library

Description

Name

formatted output to

stdio.h

const char

*,

types

int

match output arguments

screen (stdout)

that

E*N

putc

character output to text

FILE

*

stdio.h

int,

stdio.h

int

stdio.h

const char

int

file

putchar

character output to screen

int

(stdout) "V,

scanf

input from keyboard (stdin)

that

*,

types

int

match input

arguments

ft.

sprintf

formatted conversion to

stdio.h

char

*,

const char

*,

int

types that match

a string

output arguments

sscanf

formatted conversion

from a

stdio.h

string

const char

*,

const char

*,

that

int

types

match input

arguments isalpha

logical function for

ctype.h

int

int

ctype.h

int

int

ctype.h

int

int

ctype.h

int

int

ctype.h

int

int

ctype.h

int

int

ctype.h

int

int

alphabetic character

OS

isdigit

logical function for

base- 10 digit character

islower

logical function for

lower

case letter as

ispunct

punctuation character

CC3

the

document

Run makeindex on ("file.idx"

=>

file

"file.aux," "file.dvi")

the

document

Run bibtex on

document

the

("file.aux," "file. bib"

Run latex on

the

=>

file

"file.bbl")

document

to include the

("file.aux," "file.bbl." "file.ind"

Run latex on

the

document

Run dvi2ps on =>

=>

is

all

the

manual you latex

"file.aux," "file.dvi")

"file.ps")

these files,

a trace of the

files

document

the

Other intermediate and debugging compiling

new

=> "file.aux," "file.dvi")

to resolve references

("file.aux," "file.bbl," "file.ind"

("file.dvi"

file

"file.ind")

namely

commands

files are

"file. log"

and

constructed along the "file. big."

way of

For example, below

run for compiling and printing the latex version of

are reading:

Unix-Man

makeindex Unix-Man bibtex

Unix-Man

latex

Unix-Man

latex

Unix-Man

dvi2ps Unix-Man

Oftentimes you will have to run

bibtex

latex

to get the cross-references correct.

a

number of times

This

is

after

running

especially true if

you are

520

Appendix L LATEX Templates

using a table of contents, because

it

lags the references

by one compilation cy-

cle.

L.4

A L A T^X Sample

Article or

Research Paper

localhost> cat paper.tex \title{The Mating Rituals of Computer-Generated Rabbits \thanks{The research reported in this paper was funded in part by a grant from the Food and Drug Administration (contract no. P00032-95-7615) }} .

\author{Foo B. Baz \\ Zip Z. Zappo \\ Artificial Reality Laboratory \\ 3290 Bunko Hall \\ University of Cachaphony, Los Alamos \\ Los Babbaloey, AC

09002}

\date{}

\maketitle \vspace{0 5in} \centerline{ \Large\bf Abstract} \bigskip .

This paper briefly reports on the computational mating habits of computer-generated rabbits. This work is part of a research project at the University of Cachaphony, department of Surrealism, and has been supported by the FDA for 23 years...

\section{Introduction}

Qf)

The computational model of rabbit mating patterns has been widely talked about since the discovery that computer-generated rabbits have unusual behavior traits, such as...

\vspace{0 2in} .

This example Item

(

1

)

Item (2)

is fairly

The paper

typical of latex papers:

title.

Embedded

in the title

support, which

is

reference

is

an acknowledgement for financial

printed in footnote format at the bottom of the

page.

Item (3) The author lines,

list,

separated by double backslashes to produce unique

and the address of the authors.

A LATEX

L.5

Item (4) The current date, which can be eliminated

if

is

Letter

Command

File

printed below the author/address

521 list,

and

desired.

Item (5) Tells latex to print the

title.

Item (6) Begins the paper abstract. Note that the abstract on the same page with the title.

in this

document

is

Item (7) The one item of note in the generic paper is the section command, with its text argument. In latex, all numbered sequences are per-

formed during the compilation, so the author need not worry about section numbering. If sections are moved, latex reorders the numbering the next time the document

Much of the detail graph look

L.5

A lATeX

at

missing in

this

compiled.

example, because none of the

such as itemize or enumerate are used.

styles,

ual chapters

is

is

is

also kept in the

something a

Letter

"tletter tex" .

bit

"manual"

directory so that interested users can

File

a simple version of a letter format that takes a standard

document, "newletter.tex,'* as input, and produces a terhead. this

You

letter

with a technical

let-

You can do below so that a PostScript figure is includallocated for it between paragraphs, in which case the

can place a PostScript letterhead on the page easily.

by modifying the command

ed, but that

para-

more complex.

Command is

list

A copy of one of the man-

no space

letter is written

is

on top of the

localhost> cat tletter.tex \documentstyle{ letter} -* \begin{ document} \location{Marine Mammal Laboratory, \telephone{338-2125} — \ signature {Joe C. Student} \include{newletter} -* \ end { document \end

file

figure.

(T)

901 Hensil Hall}

The command file, above, remains the same all the time. When you run latex, this is the file you run it on, as with other command files. For example, a sample

command would

appear as follows.

522

Appendix L LATEX Templates

localhost> latex tletter This is TeX, C Version 3.0 (tletter. tex LaTeX Version 2.09 /usr/f 1/ jhodges/TeX3 0/usr/ local /lib/ tex/ inputs /letter sty Document Style 'letter' .) (newletter.tex [1]) Output written on tletter. dvi (1 page, 220 bytes). Transcript written on tletter.log. .

(

.

)

The source it

letter

can be called anything.

"newletter." This

as

will overwrite

When you

are done, simple save

your previous

newletter,

but

is

OK as long as the letters, or whatever, are saved under separate names. A sample source letter

newletter

is

shown below:

localhost> cat newletter.tex \begin{letter} {Foo B. Baz \\ 123 Xyz St. \\ Anywhere USA 03246}

(l)

\opening{Mr. Baz,}

(2)

Regarding our phone conversation on Tuesday, May order a .

23

would like to

I

.

\closing{best regards,} \end{letter} Item (1) This

is

(3)

in the

example

is

usually printed on the

the address

left,

which you are sending the

just prior to the

tex will print today's date above the address

letter to.

opening statement. Also,

in the

same

la-

location. Item (2)

is

the opening, which could be Dear, To whom it may concern, Shirley, etc., as you choose. Similarly, item (3) is a closing statement, and will be indented to near the middle of the page, below the last bit of text. Other letter commands are used similarly to other latex commands: enclose arguments in curly braces. The commands available for letters are

Table L.1:

latex

Letter options reference

\opening { item}

Your opening

\closing{item}

Your closing

\cc{item}

A

\encl{item}

Enclosures

gratuity gratuity

carbon copy

line

L.6

All other latex formatting

LATEX

Bibliography Examples

commands can be used

in letters,

523

such as enu-

merate, itemize, and quote.

L.6

lATeX Bibliography Examples Bibliographies are very important in academic reports, latex has a special pro-

which

cessor, called bibtex.

pulls cites out of a latex

references from a reference database, formats desires,

document, takes these

them according

to the author's

and places them back into the document. The following two sections

illustrate the

use of cites in this manual, and the format of cite references in the

reference database.

The use of bibliographies

in the

preamble and closing seg-

ments has already been discussed.

examples\cite{pc87

}

.

The example at

There

L.6.2

Document

l

Bibliographic Entries in the L T X £

L.6.1

isn't

much

to

it,

(2)

is the most straight forward of

really.

Bibliographic Reference Templates

The following are templates for various document types. I will explain the format of one. and let that serve as a basis for their use. With this and the documentation, you should be able to incorporate cites in your documents. The first thing you will notice is that there is a broad range of text types that are referenced

in the

templates subsequently.

Manual Techreport

Book Article

Inproceedings Incollection

Phdthesis

Unpublished Ch6

Inbook

bib

in

The samples below the "bib" directory.

are included in a file

named "bibtemplates bib" .

524

Appendix L LATEX Templates

localhost> cat bibtemplates.bib Sample Bibliography Templates

% %

%

The percent sign is a comment character in TeX and LaTeX. Anything appearing after a percent sign will not be compiled.

%

Each entry in one reference will be described:

%

% %

% % %

%

@techreport { joy 80a, title = "An introduction to ..." = "Joy, W.", author institution = "Computer Science year = "1980", :

.

.

%

type

=

%

month

=

%

}

(1)

%

(2!

"Manual", "September"

.

"

368

290

backquote

in

C

shell

in emacs 18 273 282 1

subtraction operator in

C

291

list all files in

A/UX

decrement operator 314 subtraction assignment operator 315 variable assignment in

C

equality operator

in

Bourne

shell

427

458

>

in

awk 416

absolute path 60 access control 93 access mechanism

C struct

353

access permissions 94

change 95 account allocations 251

break-ins 94

mail message header 27

ID 6

>= greater than or equal operator in

Is 70

xii

in

290

variable assignment in shell scripts

in

275, 281

\n

to abort mail message 25

in

C

tagged expression reference 407

in

C

301

maintainence 251 name 6

439

in in

awk 413 C 310

B

athO

security

Hayes hang up command 13

password 10 athl

actions in

make

Hayes test 409, 411 ScSc 416 < 416 >= 416

390

awk

activity

network status 234 address IP 20, 21

command

13

action

machine 20

print

mail 19 address-of operator 280, 327

AIX

line

411

membership (~) 415 field reference 412 inequalities 416 logical AND and OR 413 piping ( ) 414 printf 414 redirection (>) 414 test action 409 test pattern 409 awkward phrases field

xii

algorithm 331 alias

command name 64 alias 31, 140

I

current alias bindings 141 aliases

mail 31 mail host 21

MH38

diction

178

ampersand (&) in

scanf 280

B

process backgrounding 162

AND in awk 414 anonymous ftp 244

background 162 backquote

ANSI C 275

evaluate expression in shell 148

append output redirection 158

apropos 64 archie 245, 246 command reference 246

Bourne

in

C

in

command

452 439

repetition 164

banner

comment 269 256

print 180

extract contents

256

batch processing 17 batch programs 278

archives

software 244

baud bg

argc 346 arguments

command argv 346

line

biff 149

342 access mechanism [x] 344 double-subscripted (2-D) 344 element comparison 345 element search 345 indices 344 parallel 345 parallel array comparison 345 single-subscripted (1-D) 344 sorting 345 vector 344

article selection level

binary digits 96 binary number 96, 366 binary search 345 bit

96, 366

bitmaps 174 bitnet bits

42

per second

baud

blow up program 369 body

C

102 checking utilities 176 assignment operator 314 file

asterisk

C

file

290

1

variable tests reference

for-in-done

459

461

relational operators reference

at

command

loop constructs 3

message content in mail 24 bounced email 40 Bourne shell 135 case-esac 464

ASCII

attention

4 156

rate

blast process

in

rn48

multiplication operator in asterisk wildcard 432

4

rate

background 163

346

array 282,

Hayes

shell

shell scripts

bang

archive create

in

script creation

13

455

459

537

538

Index

script executability script testing

455

increment and decrement table 314 precompiler directives

455

standard variables reference 460

printf

formatting options reference 275

branching statement in

C

shell scripts

program banner comment 269

435

browser for

BSD

elseif, and endif 374

if,

until-do-done 464 while-do-done 462

declarations block 271

HTML documents

528

documentation 268 header block 271 statement block 271

xii

buffer 118

programming module entry point 283 exit point 283

select 125

bulletin board

45

bus error 365

relational operators

301

statement terminator

semicolon string input

(

;

)

275

282

strings

character arrays 282

#include 273 style

address-of operator

functional indentation 295 horizontal space 295

ampersand (&) 327 assignment

vertical spacing

operator (=) 290 statement 290 assignment operators table

switch-case variable

naming convention 279, 288

315

while

case sensitivity 268 comparison expressions 300

entry condition 313 initialization

loop body 3 1 update mechanism 313

optimization 277

compound statement 272

C

272

shell

command

do -while for

loop 317 entry condition 317 loop 315

file

140

test

reference 437

435

script

goto

control expression 315 initialization expression

banner 319

320 lexical scoping 320 local variable 320 main header 271 output function 323 parameter 320 default type

441

switch-case 444 while 440 while counter variable 440 standard variable reference 437 variable assignment arithmetic 428 call by reference 287, 325 canned functions 279

carbon-copy implicit

parameter type consistency 322

30

email 20

in

272

types 320 functions 319 if construct 304 iteration 3 logical connectives 308 logical operators 308 loop nesting 318 mathematical operators 290 operator precedence 290 operators assignment operator table 314

441

infinite loops

315

update expression 315 function 271, 283

1

alias

argument

logical expression

body 316

return statement

313 312

exit condition

compiler -o option 276

curly braces

295

construct 305

mail 25 case-esac ;

465 Bourne

;

in

shell

464

1

cast explicit data type conversion

cat

91

cc

email 20

in

cd

76

$HOME 76 .

.

76

295

539 warnings 278 compile-time errors 364

77 - 76 ceil

compress 260

math function library 29 change directory 76

concatenation

character count

1

computer program 266

command

77

in

find 84

in

95

mode 96 mnemonic arguments 95 SJ mbolic mode 95

shell 137

conjunction

binary

in

awk

413

contents of directory 69 control characters xiv

chown 99 chsh 150

control structure

circular reference

email forwarding 31

COBOL

C

conditional compilation 374 conditional or test if construct 303

406 child process 163. 427, 450 resular expressions

chmod

options 71

conditional

character escape

in

Bourne

shell

in

C

435

shell

copy

266

with

cp

col

file

innroff, troff 200 command 57

remote 247

copy

in

emacs

117

options 62, 63 interrogative

count++

80

repetition 164

in

command command

in

concatenation 77

207

interpreter 61, 133,

426

arguments 346 variables 428

line

as shell

in shell scripts

429

command mode in vi command override in vi 113 command repetition

103

event selector 165 command sequencing 77, 157 command shell 133

prompt 61

command command

in

in in

440

in

Bourne

shell

in

C

440

shell

463

counter variable in C shell loops 440 country-code institution-tvpe in email 22

cp 83 alias to interrogative 141

creation date listing

72

creation mask 99 cross post

terminating character 77 wildcards 73

in

rn 46

C

shell variable

in

mail

137

29

csh 427

make 389

comment

shell scripts

crt

comment in

C

count-control loops

file

latex

text in

key 63

command command

83

emacs 124 core dump 381 corrupted file 258 cos math function library 291

140 arguments 62 alias

buffer

457

curly braces in

character shell 137

C C shell (#) 432 latex 204

comment-out source code 270 communications electronic 18

communications etiquette 17 comp 36 compilation 266 parse 267 compile text formatting 86 compiler 266 1

C

modules 272

current directory 68 current message pointer 27

cursor in text editins

103

cycle in

C

shell loops

437

D data transmission rate 4

data type 352 array 281 coercion 294

540

Index

FILE * 355 struct 352 declaration 358 field variable access 358

date

display in

MH

40

display message range

mail 30 document

149 debug 267 debugger

print

179

shell scripts

document body 204 document translation 185 documentstyle 204, 208 design 527 domain mail 22

trace function

dot

Gnu Debugger 380 debugging 278

dummy

functions 377 function drivers 379

433 372 decimal number 366 default printer 180 default values

command arguments 63

in

123

relation

make 390

in

diction 178 diff 83, 88

drafts folder

options reference 89

in

MH

direct text modification 107

directory 58

dvi 205

access control 93

change 76 contents 69 creation 78 current or working 68 flat 75 home 67 list contents 69 owner 67 ownership 93 parent 71

C

shell 427 debugging shell scripts 434 quoted arguments 434 shell variable value 69

removal 79

deep 75 shallow 75

dirs 140 disjunction in

awk 413

disk block 255 disk hog 255 disk space allocation 251 disk usage 254

contents 91

edit in latex compilation 207 Ecapsulated PostScript (EPS) 174 echo 6, 144, 158 Bourne shell 451

relocate 79

subtree

telephone number 13

E

permissions 93

recursive 81

dial

dvi2ps 205 dvips 205

path 60, 68

removal errors 80 rename 79 root 58 shorthand 68

40

dt

du 254 dump file cat

direct login 3

loop 317

laser printing 182

Hayes

366 96

and customization 426

awk 417

do -while draft mode

digits

70

double dot directory 71 double quote

device capacity 254 df 252, 253 field name reference 253

digit

lists

utility initialization

emacs

dependency

188

dot directory 71 dot file 9, 134 in directory

delete text in

command innroff

edit

MH

in

40

editable file 102 editor full

screen 101

line si

102

ream 102

VI file

access 102

egrep

83, 408 operator reference 88 options reference 88

electronic

communications mail 18

]

X

541 news 45

exp

math function

42

talk

emacs

explicit type conversion

118

key 118

cast

command

buffer

copy

1

text

1

24

exit

from

file

access 1 18 finding 118

file file

1

global effects command reference global options 126

incremental save 125 kill

mode

1

1

26

fclose

125 reference

1

27

126

fgrep in

if-else

delimiters in

awk 409 specifier

scanf

printf,

305

291

access mechanism 358

305

C 290

structure

357

field variable

for

struct 352

file

access 102 attributes listing 72 compression 260 copy recursive 83 creation 102

creation date in

364

error propagation 278,

364

errors

recoverable 278 escaping characters 406 etiquette

communications 17 in talk 43 network 18, 228 event selector repetition 165

executable file 276 execute permissions 95 execution path 146 //

awk 413 awk 412

matcher

EPS 174 equal sign

exit

83, 87, 453 process redirection 160

variable

OR if-else-if

command

350, 351, 355

field

reference 128

347 end-of4ine character 347 environment variables 68, 146, 429 EOF 347

in

loop control 440

278

foreground 162

end-of-file character

in

library 291

fg

Encapsulated PostScript (EPS) 181 encryption schemes in rn 52

error flag

type option 70

file

math function

AND

nested

embedded

452, 463

Is

word delete 123 email 18 email problems returned mail 41 service unavailable 41 system down 41

embedded

shell

fatal errors

command

utilities

Bourne

if 304

selecting a buffer 125 string search

in

while

open buffers 125 meta key 1 1

session

454

falling through

123

file

shell

fabs

1

list

save

Bourne

-F

buffer 125

kill text

in

expr

F

1

manipulation command reference 126 modification command reference 124

interaction

295

export

1

cursor control command reference 122, 123 cursor movement 122 delete text 123

file

library 291

explain 779

116

cntl

441

exit criterion

posting articles 49

Is -1

listing

display with more 90 dump with cat 91 locate

with string search 86

opening 102 ownership 93

Is -1

listing

path 60 permissions 93 reading from f scanf 350 relocation (mv) 82

removal 81 rename (mv) 82

72

72

542

Index

Is -1

revision date in

save

Is -1

size in text

emacs

in

listing

72

function

125

application

listing

72

347

type 70 writing to with fprintf 351 FILE * data type 355 file

copy 83

file

insertion

324 319 types 320 function call 274, 319 zero arguments 333 function driver 379 side effect

structure

vi 14 commands vi 112

in

1

file level

in file

merge

file

permissions octal and binary codes 98

file

pointer

file file

system 57 system management 251

file

transfer protocol

file

1

14

variable

C

function libraries user-defined 385 functional context 272

347

242

filec

shell variable

G gcc 275

138

58

files

compiler options 276 383 command reference 382 option reference 381

gdb

find 83, 84 command

options 86 options reference 86 use of wildcards 84

global effect in

find file in

emacs

1

18

1

12

global options

emacs

host 230

126

global search

43

login status user 230 finger file 230

remove extension

230

439

1

goto in

rn 46

grep

floor

math function

(:r)

Gnu C compiler 275 Gnu Emacs 15

flame 18 in

commands

file-level

invi 107

433

finger 229

talk

vi

global modifications

finding errors in scripts

in

320

320, 323 mixed parameter types 328 parameter call by value 324 prototype 284, 322 call

library 291

flow control

Bourne shell 457 folder 36 f open 348, 355 f oreach 438 in C shell 438 in

C

shell

441

83

example 145 family options reference 88 operator reference 88 group permissions 94

H

foreground 162 for-in-done in

Bourne

shell scripts

forking a shell 163. 427,

FORTRAN

266

f orw 36

forward email 31 fprintf 351 f scanf 350, 355, 359

ftp 242 binary 258 reference 243, 244

command

in

prompt 245 prompt 243 path 60 default

latex

compilation 206

hardware platforms xii Haves command set 13 head 91, 92 header file 273, 385 heading

innroff

192

headings

man page 65 high-level languages

history

ftp>

lull

help

461

450

266

139. 163

histon,

C home

shell variable

director) 6.

139

67

creen editors 101

.

543 mode vi 103 INT_MAX 368

home page

insert

WWW 531

host 5

hostname

HTML

INT_MIN

148

368

integer overflow error 367

528

document control options 528

interaction

figure control 53

font type options

529

interactive

paragraph style options 530 section header options 529 hung process 156 Hyper Text Markup Language (HTML) 185, 528

mode

emacs

in

17

1

program 278

interchange format 185

42

internet

20

Internet Protocol

intervention in infinite loops 441 IP address 20, 21 is a member of

I

awk 415

in

iteration

enter insert

mode

in

vi

105

I/O or 10 273 idle time with rwho 236

if 304 conditional or test 303 syntax of construct 303

C

shell

437

event accumulation 318 event counting 318 event selection 318 iteration in C 311 iterative refinement 283, 31i

if-else 303 C shell 435 if-else-endif

C

job 162

shell scripts

parentheses 435

number 162 print 181

if-else-fi in

Bourne

457

shell

remove

print 182

jobs 162

if-endif in cshrc 137 implementation file 386 implicit type conversion 294 inc 35, 36 .

K

include file in

email message 25

file in

latex 207

include files 385 include statement 273 increment operator 3 1 postfix 313 prefix 313 increment, decrement operators table

314

communications package 13

kermit

156 key bindings in

129

standard input 133 kill

342 338

awk 416

infinite

loop 369

emacs

125

emacs

123

kill text

in

inequalities in

buffer in

indirection operator

C

emacs

keyboard

indirect login 3

in

64

kill 156

indexing in arrays

man option kermit

kilobytes 254

shell scripts

441

kleene star 405 Korn shell 135

information shared 228 initialization file

inline

134

commands

in

latex 209

inner loop 318 input function 280, 324 input parameters 287

long listing

Is

star closure

of language

option 70

L*

L 404

J

544

Index

modem 4

language 401 concatenation operation 401 difference operation 401 intersection operation 401 star closure operation 401 union operation 401

network 4 terminal server 4 login shell 9 login status in finger 230 logout //

laser printer 181

last 233 latex 204

long listing 70

look

compilation e, x,

h debugging commands 206

font size options reference 2 font type options reference

body 311 control expression 3 control variable 3 in

1

217

commands 209 commands 209

1

sed 418

commands in

latex 209

line continuation character in

line

line printer

line

C

281

count 177

437

in

Bourne

shell

461

loop control variable in

Bourne

C

shell loops

461

438 looping in C shell 440 looping mechanism 31 low-level language 266 in

shell loops

lpq 181 lpr 179 command lprm 182 Is 69 -a -F

option option -1 option -R option

112

line editor 102,

shell

loop body

pagecontrol options reference 217 paragraph style options reference 219 reference control options reference 221 resume template 514 section header options reference 218 texformats path 49 texinputs path 149 leaf or terminal 58 line address range in

C

1

1

pass or cycle 313 update mechanism 313

inline

line

776

loop

document control options reference 216 documentstyle design 527 figure control options reference 220

line

prompt 6

login

180

option reference

70 70 70 75

range

vi

file-level

linear search

commands

1

12

345

M

LISP 266 list all list

70

directory contents

Is 69 In

symbolic link 169 load average 241

log

math function log out

I

MACH

library 291

nroff mail

institution-type

function in math library 291 logical connectives 308 logical expression in

C C

commercial 22 country-code 22 dialup 22 educational 22 government 22

300

435 300

shell

logical flags

22 network 22 military

logical test in

C

shell

137

logical tests in

190

I

log 10

in

xii

machine remote 241 machine address 20 machine language 266 macro in make 389

awk 413

login

organization 22 message abort 25 message content 24 path 27

direct 3 indirect 3

ID 6 remote 3 login

mail

19, 23, 24 display message range 30 institution type reference 22

1

80

n545

minimum

path 27

mkdir

read message reply to

number 27

message 30

commands 34 command options 34

special (~) tilde

mail aliases 31 mail bouncing 32

Mail Handler Rand Corporation 35 mail

ram 36 scan 36 send 36 show 36

internal command options 33, 34 message header reference 28, 29 message list reference 26 message pointer 27 paging 29

mm

innroff modem 4

MAIL

UNIX

make

387, 388, 394

subdirectories

60

motd

comments 389 dependency 388 macros 389 task actions 390 makefile 388 Makefile 388 makefile 388 make index 526 man 63

-k information man macros innroff 190 man page xvi, 63

move cursor invi 107 ms macros in

option 64

mv

emacs

address 280, 327 value 280 files in

mail

message of the day 7 Meta key 1

18

35 aliases

38

comp comp

147

36

ref ile 36 repl 36

next occurrence in string search 66 21

name address convention name alias in finger

name

230

server

problems with email 41 in

40

execution path 147

prev

N

nested

folder 36 f orw 36 inc 36 next 36

rename 82

negation

36

drafts folder

relocation 82

file

n

25

mesg 45 emacs

file

interrogative 82

maximum integer value 368 me macros innroff 190 memorv 280

in

79

directory renaming 79

65

124 markup language 1 85

MH

190

alias to interrogative 141

text

in

nrof f

multiplexer 12 multi-tasking 133 multi-user operating system 133

directory relocation 79

more

merging

7

mounted device 252 mounting a device 58 mounting point 254

display

in

display 65

next occurrence (n) 66 options reference 90, 91 reading saved mail 30 string search 90

31

lists

90

man page

major

mark

190

standard output 133

more

23 23

variable 146

mailing

368

moderated newsgroup 49 modular design 370 modular programming 318, 330 in debugging 374 monitor

utility

mail

MH

integer value

78 macros

C

awk 413 if-else shell

444

nesting decisions in

C

305

netiquette 18

network activity

234 228

etiquette status

of a host with ping 239

546

Index

uptime and newline character 347

ruptime 239

paging

utility

(pager)

more

65 paragraph environment in nrof f 192

newsgroup 45 36 755

next nice

345

parallel arrays

non-terminating loops 369

parameter

notify

parent directory 7 parent process 163 parent shell 427, 450 in process multi-tasking 162 parentheses operator precedence 29 parse

C shell variable nrof f 187

138

1 95 193 hyphenation control option reference 196 line control option reference 194

font type/size control option reference

formatting

utilities

macros

in

man package 190, 198 me package 190

mm package ms package

190 1

90

awk

PASCAL

271, 286

script

417

266

pass in C passwd

man macro

options reference 202 margin/tab control option reference 194

list

shell loops

437

11

account access control 94

password 6

me macros

selection advice 10

who

column control option reference 197 heading control option reference 197 paragraph style option reference 198 miscelaneous options reference 196 page control option reference 193 plain 190

can change 10

path directory 68

mail 19, 27 pattern delimiter

405

pattern matching 399, in

404

vi 404

period notation

O

in

struct

access, reference 353

permissions execute 95

-o

C

C compiler option 276 object code 266 off-by-one errors 314, 369 offensive postings to rn 52 online manual xvi

operating system xii, 3 multi-tasking 133 multi-user 133 optional command arguments 63

OR in

group 94 other 94 owner 94 read 95 types 95 write 95

compiler option 277

pipe 32, 160 piping

awk 414 nrof f 190 Pnews 49 in

plain

posting to a newsgroup 49

awk 413

ordinal position shell variable reference 453 other permissions 94 outdated phrases

diction

ping 239

178

outer loop 3 1 output function 280, 323 output parameters 286

owner permissions 94

pointer 287, 325 to a UNIX file 169

popd

140 postamble in

latex 204

postfix increment operator 428,

440

posting to a newsgroup 49

Postmaster in email 20 PostScript 174, 181

pow

page layout 208 pager 29

more 90 PAGER variable

148

math library function 291 preamble in latex 203, 207 in nrof f 192 precompiler directives if, elseif, and endif 374 in C 273

q547 prev

object code 266

36

object code execution 276

print

printf

debugging 370 330 source code 266 stub 286 style 267 syntax errors 364 task decomposition 283 programming language 266 grammar 266

banner 180 document 179 job 181

solution feasibility

printer laser 181

180 queue 181 printf 272 line

control string

274

numbers 293 debugging 370 format examples for integers and strings 293 format options 274 in awk 414 procedural abstraction 283, 330

interpreter4oased

field specifiers for real

PROLOG

LISP.

for

425

267 semantics 266 syntax 266 portability

project organization

make 387 prompt 5, 7 prompting Bourne shell 454

process 133

backsround subshells 162

156 execution blast

prototype declaration 357 with structures 357 pruning in search 345 ps 151 display field reference 152 execute field reference 152 options reference 154 removing header with sed 420 status priority reference 153 status swap field reference 153

background 162 foreground 162 execution status 152 foreground 162 ID number 162 memory status 153 piping 160 priority 153 redirection 157 remote 241 remove or kill 156 stacking 162

pseudocode 338

status f51

public software archives 244

stop 162

pushd

stopped 156 process pipe in conjunction with

in

more

90

program xii bugs (errors) 267 header 27 program crash 365 program design

quota

364 332

off4oy-one 369 operator precedence 369 propagation 364 run-time 365 execution escape 371 expressions 266 flagging errors 364

266 modular design 370 instruction

name

reference 252

quote

Bourne in

shell scripts

(

" )

awk 417

quoting the arguments in

compile-time 364

251

field

errors

library include

ftp 258

pwd 68

Q

iterative refinement 318 program stubs 375 programming commenting out debug statements 371 debugging 278 stubs 375

lexical

140

put

echo 434

R -R

Is

recursive option 75

rep 248 read

mail message

27

read in

Bourne

shell

read permissions 95

454

459

548

Index

reading from

350

recoverable errors 278 recursive copy 248 recursive descent directory contents listing 75 recursive file removal 81 redirection in

in

encryption schemes 52 newsgroup selection options 51 pager selection options 53

file

f scanf

awk 414 mail 25

47

startup

root directory 58

254 volume 254 rsh 250

root disk root

run-time error 365 ruptime 239, 241

rusers 237

mail messages 25 reference operator shell variable 69

ref ile

36, 40 regular expressions

400

full

symbol reference 408 421 pattern matching 404 special characters 408 special symbol escape 406 symbol references 406 regular language 404 alphabet 401 empty word 401 in

sed

401 infinite 401 word 401 finite

relational operators

300

mv

mail message 30 save-some-buffers in emacs 125

scan

for

82

in

command vi 111

vi

circularity in

linear

345

mode

in

vi

250

account 10 security risk .

156

sed

rename file 82 repl 36

rhosts 94

417, 418

command

options reference 422 range 418 regular expression 421 shell variables 421 line address

replace text

invi 110 reply

segmentation

30

fault

365

selecting a buffer

resource sharing 228, 242 response time -1 return statement 272 return statement for void function 286

rlogin 249 rmSI

in

emacs

125

selecting passwords 10

SELF-PACED semicolon

( ;

xvii

)

command

sequencing 77 275 send 36, 39 sequenced commands 157 in

interrogans 141

79

rntm 36

C

service unavailable 41

45, 46

set

.news re 46

139, 427 in

article selection level

article selection

66

security

remove process

alias to

111

111

more

option in

users 237 who 236 kill

modification 167

binary 345

processing 241

rn

451

in

machine 241 port 4

rmdir

debugging 371

search 345 and replace

login 3

mail

36

scanf

remote copy 247

shell

342

scalar variable

script

302

with

26

scheduling priority process 153 screen dumps 174

relocation file,

mail

scanf 279

rehash 457 table of

subject header option in

save

48

options 52

sh

C

shell

450, 456

138

549 shared information 228 shared resource 228, 242

status variable

shell

stdin

Bourne

standard input

shell

variable assignment 451

C

437

script

command comment

line

arguments 429

character

432

debugging 433 trace debugging 433 variable assignment 427 variable

environment variable 429 in sed 421 numeric 427 path 146 reference 146

427

string

prompt 7 399, 425 character 137

dot file scripts 425 login scripts 425 shell variable 427

Bourne

shell

451

138 history 139 notify 138 shorthand directory notations 68

show 36

debugging 380 stop a process 162

stopped process 156

strcmp strcpy

274 comparison 358 in search 64 string arguments in echo 434 string

string search

for file location

vi

in

111

data class 352 element access 353 field variable 352 hierarchical organization

354

type 352 variable declaration 353 structure

352

tag

type 352 structured variable 342 array 342

login style 177

72 254

style file

listing

slash disk

145

library function 291

size

in

.

19

208

sub-shell in

345

process multi-tasking 162

subshell 163,

Bourne

source

innroff source 151

sqrt

math function library 291 square brackets shell

427

shell

450

switch-case construct in C 305 in C shell 444

190

source code 266 spell 175, 176

Bourne

143

subdirectory 59

smiley face, :-) software xii

458

stack

directory access 140 stack frames

debugains 384

standard input 25, 133, 150, 157, 350 standard output 133, 150, 157 status file

86

emacs 126 in more 90 in

structure 351

math

in

358 350, 355

stream editor 102, 417

stty

sin

in

pointer 351

declaration 357

shell

filec

sorting

file

struct

shell script 134,

comment

pointer 350

step through

programming interpreters 425 programming language 399 remote 250

C

file

stdout

standard output

shell

iteration

shell

f scanf 350

scanf,

70

of processes 151

switching station 12 symbolic address 21 symbolic link 169

symbolic name 21 syntax errors 364 system administrator 14

system

down

email problems 41

system hogs 229

System

V

xii

550

Index

u Ultrix xii

tag

407

regular expression

in

tag-based language 528 Tagged Interchange Format (TIFF) 174 tagged regular expressions 407 tail 91

talk 43 etiquette

43

exit with

44

library function 291

tape archival 242, 256

tar

242, 256

command

reference 259

256 256 file selection 256 verbose (v) 256 create (c)

extract (x)

99

login 145 uncompress 260 UNIX xii, 3 in

.

untar 257 until-do-done in

tan

math

umask

Bourne

uptime

shell

464

239, 240

Usenet 42 user 6 user ID 6 userid 6 USER variable 146 user-defined structures 357 users number of 241

users 237 remote 237

target value

uucp 42

search 345 161, 409

in

tee telnet 249 command

reference 250

telnet>

prompt 250

vacation

term

C shell variable termcap file 144

138

declaration

struct 353 environment 146

terminal 5 terminal characteristics 5 terminal server 12 test-expression in

Bourne

shell

shell reference operator

declaration 358

if 457

structured array

function drivers 379

1

1

variable assignment

347

text formatter

in

185

verbose

text readability

with style 177 text source file 186 thesaurus awkward phrases 179 TIFF 174

69

commands

in

mail

in

C

34

include mail message 25 timesharing 5

vgrind vi

in shell script

debugging 433

option reference 183

102 :r 114

toggle out of insert mode command mode 03 command override (!) 113 cursor exit

movement

from (ZZ,

352, 357

file

manipulation

file

merge

I

1

13

command

reference

14

commands (:) 112 command reference 15 global effects command reference i (insert text) command 105 file-level

mode 103 cursor 107 replace character

1

insert

typescript

move 451

106

reference 109

:wq)

global

t\pc declaration 271

m script

138

182

command

trace

trof f 1H9 tset 143, 144

shell

mode ftp 242

1

tilde-r

file

352

unpredictable value 368

altering text

typedef

342

structure

text editing

tilde (~)

69

struct

testing

text file

32

variable

r 110 scope of cursor movement 109 (

)

1

12

1

14

w 551 search and replace 1 1 search mode 1 1 text alteration reference 110 text insertion reference 106 void function 286

W w238 field description reference

238

wc 177 What Now options in

What You See where is 93

which

MH is

40

What You Get 185

92

while in

C

shell scripts

440

uhile-do-done in

Bourne

462

shell

who 235 am option 229 in talk 43 i

remote 236 i 9, 229

who am whoami

229

8.

wildcard (*) in file

removal 8

wildcards in

find 84

word count 177 word delete in

emacs

123

working directory 68

World Wide

Web (W3)

185

write permissions 95 writing to a file

fprintf

WWW

351

home page 531

WYSIWYG

185

X X in

rn

52

x exit in

XENIX

latex

compilation 207

xii

ZZ exit

from vi

1

1

STUDENT

L SERIDs

AND ALIASES

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

Name

UserlD

Mail Alias

GROUP ALIASES

Userids in Alias

Group Alias Name

Userids in Alias

Group Alias Name

Userids in Alias

Group Alias Name

Userids in Alias

Group Alias Name

PRINTER INFORMATION Printer

Type

Printer

Network Name

Printer Location

:

—

INTRODUCTION

TO

Berkeley UNIX and ANSI C JACK HODGES For anyone who wishes to

use, understand,

and appreciate the

UNIX operating

system, this text provides the framework for a self-paced, self-teaching course. This timely volume introduces a widely used version of Distribution or Berkeley

UNIX, and

UNIX known

the functional basics of the

language. Using plain language, author Jack

Hodges

as

Berkeley System

C programming

divides coverage into three

main

parts:

The UNIX Operating System The C Programming Language System Programming with C and UNIX.

He

discusses the elements of programming and the interactions that the operating system mediates between the user and the computer in generic terms, making the

concepts easily applicable and transferable to any hardware platform, language, or data

file.

In addition. •

BSD

UNIX and ANSI C: widely used UNIX type

Introduction to Berkeley

Introduces readers to one of the most the

1

An

operating systems

dialect.

Offers numerous examples tested in the Ultrix

UNIX dialect,

including examples

•

executed on a number of BSD-compatible UNIX hardware platforms. Provides a conversion table for all examples presented in the text in a separate

•

Develops a fundamental working knowledge of

appendix. simple but correct use of syntax, programming

program

C

for

style,

programming, including

debugging, and logic

in

simple

writing.

In addition. Jack

Hodges encourages

i

shares with other languages since the?

new programming

skills easier later

o

_!

\

3-068495-3

PRENTICE HALL Englewood

Cliffs,

NJ 07632 099 I

it ii

I

II III

60 138 "684958

..j..