A practical guide to Linux commands, editors, and shell ...

A Practical Guide to Linux@ Commands, Editors, and Shell Programming THIRD EDITION

Mark G. Sobell

PRENTICE

HALL

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Brief Contents Contents Preface

1

xvii

xxxvii

Welcome

PART I

Linux

to

Getting Started

3

The Utilities

4

The Filesystem

5

The Shell

21

23

81

125

The Editors

The vim Editor

7

The

emacs

157

159

Editor

213

The Shells

8

The Bourne Again Shell

9

The TC Shell

PART IV

1

49

6

PART III

Mac OS X

The Linux and Mac OS X Operating Systems

2

PART II

and

(tcsh)

273

(bash)

275

369

Programming Tools

10

Programming the Bourne Again Shell

11

The Perl Scripting Language

415 (bash)

417

517

xv

xvi

Brief Contents

12

The Python Programming Language

563

13

The

14

The AWK Pattern Processing Language

15

The sed Editor

MySQL Database Management System

595 619

653

Secure Network Utilities

PART V 16

The rsync Secure Copy Utility

17

The OpenSSH Secure Communication Utilities

PART VI

PART VII A

673

Command Reference

Command Reference

713

Appendixes

Regular Expressions

B

Help

C

Keeping

D

Mac OS X Notes

1009

1011

1021

Glossary

the

1053

File Tree Index

UtilityIndex Main Index

System Up-to-Date

1105 1107

1111

1041

671

1027

711

687

Contents Preface

xxxvii

Chapter 1: Welcome to Linux and Mac OS X The

History of UNIX and GNU-Linux Heritage of Linux: UNIX 3

1

3

The

Fade

to

1983

3

Next Scene, 1991

4

The Code Is Free Have Fun!

5

6

What Is So Good About Linux?

Why

Linux Is

6

Popular with Hardware Companies and

Linux Is Portable

The C Programming Language Overview of Linux Linux Has

10

11

Programming Interface 12 Support Many Users 12 Can Run Many Tasks 12 Provides a Secure Hierarchical Filesystem a

Developers

10

Kernel

Linux Can Linux Linux

12

The Shell: Command Interpreter and Programming Language A Large Collection of Useful Utilities 15

Interprocess Communication

System Administration Additional Features of Linux GUIs:

Graphical

16

User Interfaces

Utilities

(Inter)Networking Software Development Chapter Summary Exercises

18

16

16

18

18

17

16

14

9

xviii

Contents

PART I

The Linux

Mac OSX

and

Operating Systems

21

Chapter 2: Getting Started Conventions Used in This Book In from

Logging

a

Terminal

24

(Emulator)

from the Command Line

Working

Which

29

29

Correcting Repeating/Editing Command Where

26

28

Shell Are You Running? Mistakes

su/sudo:

23

Lines

31

Curbing Your Power (root Privileges) 33

Find Documentation

to

man:

Displays

the

System

Manual

33

apropos: Searches for a Keyword 35 info: Displays Information About Utilities The

32

36

38

—help Option help Command Getting Help 39 The bash

39

More About

Logging In and Passwords 42 Log In 42 Logging In Remotely: Terminal Emulators, ssh, and Dial-Up Connections Using Virtual Consoles 43 Logging Out 43 Changing Your Password 44

What

to

Do If You Cannot

Chapter Summary Exercises

46

46

Advanced Exercises

47

Chapter 3: The Utilities Special Characters Basic Utilities Is: Lists

50

51

the Names of Files Text File

cat:

Displays

a

rm:

Deletes

File

less Is

a

52

Display a Text File One Screen Displays the System Name 53

Working with Files cp: Copies a File mv: Changes the Prints

grep:

52

52

more:

hostname:

Ipr:

49

a

53 53 Name of a File

File

Searches for

55 a

String

56

54

at a

Time

53

43

Contents

Displays the Beginning of a File 56 Displays the End of a File 57 58 sort: Displays a File in Order Removes Lines from a File Duplicate uniq: 58 diff: Compares Two Files

xix

head: tail:

file: Identifies the Contents of

I

(Pipeline): Communicates

Four More Utilities

date:

script: Records

File

60

Between Processes

a

Date

Shell Session

unix2dos: Converts Linux

Files

62

62 to

Windows and Macintosh OS X Format

Compressing and Archiving Files 63 bzip2: Compresses a File 64 bzcat and bunzip2: Decompress a File gzip: Compresses a File 65 66 tar: Packs and Unpacks Archives Locating Utilities

locate: Searches for

a

a

File

68

Utility 70

System Information Displaying 70 who: Lists Users on the System Users the 71 on Lists System finger: User and

uptime: Displays System Load and Lists Users

the

System Displays Memory Usage

free:

65

68

which and whereis: Locate

w.

on

70

Duration Information

73 Information 74

Communicating with Other Users 74 write: Sends a Message mesg: Denies or Accepts Messages Email

Chapter Summary

76

79

Advanced Exercises

80

Chapter 4: The Filesystem The Hierarchical

82

Filesystem

Directory Files and Ordinary Files Filenames The

75

76

Exercises

84

Working Directory Directory

Your Home

Pathnames

60

61

Displays Text 61 Displays the Time and

echo:

a

58

86 87

87

Absolute Pathnames Relative Pathnames

88 89

83

81

74

72

63

xx

Contents

Working with

Directories

mkdir: Creates cd:

Changes

a

90

Directory

Another Working

to

rmdir: Deletes

90

Directory

a

Using Pathnames 94 mv, cp: Move or Copy Files 95 mv: Moves a Directory

94

Important Standard Directories and Files Access Permissions

92

Directory

93

95

98

Is -1:

Displays Permissions 98 chmod: Changes Access Permissions Setuid and Setgid Permissions 101 Directory

Access Permissions

ACLs: Access Control Lists

99

103

104

Enabling ACLs 105 Working with Access Rules 105 Setting Default Rules for a Directory Links

Hard Links

Symbolic rm:

110

Links

Removes

a

112

Link

115

Dereferencing Symbolic Links Chapter Summary Exercises

119

122

Chapter 5: The Shell The Command Line

Simple

125

126

Command

126

126

Syntax

Simple Commands 130 Processing the Command Line Executing a Command 132

Editing Standard

the Command Line and Standard

Input

The Screen The

as a

File

Pipelines Lists

133

Output

133

as

Standard

Input and Standard Output

135

141

145 a

Command in the

Background

Filename Generation/Pathname The ?

Character

Expansion

148

Special Special Character 149 The [ ] Special Characters 151 The

130

134

Keyboard and Screen

Redirection

Running

115

120

Advanced Exercises

A

108

109

J>"

146 148

135

Builtins

153

Chapter Summary

153

Utilities and Builtins Introduced in This Exercises

PART II

156

The Editors

157

Chapter 6: The vim Editor

159

160

Tutorial:

Using vim to Create and Edit Starting vim 161 Command and Input Modes Entering Text 164

Getting Help

to

vim Features

Online

168

161

Work Buffer

171

168 168 168

Help Terminology 169 Modes of Operation 169 The Display 170 Correcting Text as You Insert Length and File Size

Windows

File

165

Ending Editing Session The compatible Parameter Introduction

a

163

the

Line

154

155

Advanced Exercises

History

Chapter

It

170

171

171

File Locks

171

Abnormal Termination of

Recovering

Text After

a

an

Editing Session

Crash

172

173

Command Mode: Moving the Cursor Moving the Cursor by Characters

174 175

Moving the Cursor to a Specific Character 175 Moving the Cursor by Words 176 Moving the Cursor by Lines 176 Moving the Cursor by Sentences and Paragraphs Moving the Cursor Within the Screen 177 Viewing Different Parts of the Work Buffer 177 Input Mode 178 Inserting Text

178

Text

178 Appending for Text Line Opening a

Replacing

Text

178

179

Quoting Special Characters

in

Input Mode

179

177

xxii

Contents

Command Mode:

Deleting and Changing Undoing Changes 179 Deleting Characters 180 Deleting Text 180

Changing Text Replacing Text Changing Case

Text

179

181 182 183

and

Searching Substituting 183 Searching for a Character 183 Searching for a String 184 Substituting One String for Another Miscellaneous Commands

190

190

Join Status .

190 190

(Period)

Copying, Moving, and Deleting Text The

186

General-Purpose

Buffer

190

191

Named Buffers 192 Numbered Buffers 192 and Writing Files Reading Files 193

Reading

193

Writing Files

193

Identifying the

Current File

Parameters

Setting Setting

Setting

194

194

Parameters from Within vim Parameters in

a

Startup

The .vimrc Startup File Parameters 195 Advanced

194 195

195

Editing Techniques Using Markers 199 Editing Other Files 200 Macros and Shortcuts

File

199

200

Executing Shell Commands from Within Units of Measure Character Word

203

203

203

Blank-Delimited Word Line

204

Sentence

Paragraph Screen

204 205

(Window) Factor

Repeat Chapter Summary Exercises

206

206 206

211

Advanced Exercises

212

204

vim

201

Contents

Chapter 7: The emacs Editor

213

214

History

Evolution emacs

Tutorial:

214

Versus

215

vim

Started with

Getting

Starting Exiting Inserting

218

Deleting

Characters

Text

218 218

Moving the Cursor 219 Editing at the Cursor Position

Saving

and

216

emacs

216

emacs

Retrieving

221

the Buffer

222

Basic

Editing Commands 223 Keys: Notation and Use 223 Key Sequences and Commands 224 META-x: Running a Command Without a Key Binding Numeric Arguments 225 Point and the Cursor

Scrolling Through Erasing

Text

a

225

Buffer

225

226

Searching for

Text

226

Using the Menubar from the Online

Help

228

Keyboard

229

Advanced

Editing 232 Undoing Changes 232 Point, Mark, and Region 233 Cut and Paste: Yanking Killed Text Inserting Special Characters 236 Global Buffer Commands

Visiting

and

Saving

Files

235

237 239

242

Buffers

243

Windows

Foreground Shell Commands Background Shell Commands

245

246

Major Modes: Language-Sensitive Editing Selecting a Major Mode 247 Human-Language Modes 247 C Mode

250

Customizing Indention Comments

Special-Purpose Modes Customizing The

emacs

.emacs

Sample

.emacs

254

256

Startup File

Remapping Keys A

253

253

257

258 File

259

246

224

xxiii

xxiv

Contents

More Information

Access

260 261

Chapter Summary Exercises

261

to emacs

269

Advanced Exercises

PART III

270

The Shells

273

Chapter 8: The Bourne Again Shell Files

278

Login Shells Interactive

278

Nonlogin Shells

Noninteractive Shells

(Dot)

source: Runs

or

Commands That Are

Redirecting

279 a

chmod: Makes

a

Startup File

Symbols

Standard Error

Writing and Executing

a

279

279

Setting Up Startup Files .

in the Current Shell

281

282

Simple Shell Script

File Executable

284

285

Specifies a Shell 287 Begins a Comment 288 Executing a Shell Script 288 #!

#

Control Operators: Separate and Group Commands 290 ; and NEWLINE Separate Commands

289

I and & Separate Commands and Do Something Else && and II Boolean Control Operators 291

( ) Groups Commands \ Continues

Job

Control

a

293

294

Suspending bg: Sends

292

Command

jobs: Lists Jobs fg: Brings a Job a

295 to

the

Foreground

295

296

Job Job to the Background a

296

Manipulating the Directory Stack 297 297 dirs: Displays the Stack pushd: Pushes a Directory on the Stack popd: Pops

a

Directory Off the Stack

Parameters and Variables

300

User-Created Variables Variable Attributes

305

Keyword Variables

307

Special Locale Time

Characters 316 320

275

276

Background Startup

(bash)

315

302

298 299

290

280

Contents

Processes

323

Process Structure

323

Process Identification

Executing

a

324

Command

325

326

History

Variables That Control

History 326 Reexecuting and Editing Commands The Readline Library 335 Aliases

328

342

Single Versus Double Quotation Marks in Aliases Examples of Aliases 344 Functions

346

Controlling

bash: Features and

bash Command-Line Shell Features

Options Options 349

Processing History Expansion Alias Substitution

Parsing

349

350

the Command Line

and

343

354

354 354

Scanning the Command Line Expansion 354

354

Command-Line

Chapter Summary Exercises

364

366

Advanced Exercises

368

Chapter 9: The TC Shell Shell Scripts

(tcsh)

Entering and Leaving the Startup Files 372

TC Shell

Features Common to the Bourne

Command-Line

Job Control

371

Again and TC Shells

Expansion (Substitution)

378

Filename Substitution

378

Manipulating the Directory Stack Command Substitution

379

Error

379

Redirecting Standard

Working

with the Command Line

Word

386

String Variables 386 Arrays of String Variables Numeric Variables

Special

383

385

Variable Substitution

Braces

380

380

Completion Editing the Command Line Correcting Spelling 384 Variables

369

370

387

388

390 Variable Forms

tcsh Variables

391

391

379

374

373

xxv

xxvi

Contents

Control Structures if

398

398 401

goto

Interrupt Handling foreach

401

402

if...then...else 403 405

while

405

break and continue 406

switch Builtins

407 411

Chapter Summary 412

Exercises

Advanced Exercises

414

Programming Tools

PART IV

415

Chapter 10: Programming the Bourne

Again Shell (bash) 418

Control Structures if...then

419

if...then...else

423

if...then...elif for...in for

425

431

433

while

435

until

439

break and continue

441

442

case

select

448

Here Document

File

417

Descriptors

450

452

File Descriptor 453 Duplicating a File Descriptor 453

Opening File

a

Descriptor Examples

Determining Whether Parameters

Special

453

File Descriptor Is Associated with the Terminal

458

Positional Parameters

Variables

a

Parameters

458

463

467

Shell Variables

467

Environment, Environment Variables, and Inheritance

Expanding Null and Unset Variables Array Variables 474 Variables in Functions

475

472

468

456

Contents

Builtin Commands

476 Information About

type: Displays read: Accepts User Input exec:

Executes

Command

a

trap: Catches a Signal kill: Aborts a Process

a

or

Redirects File

A Partial List of Builtins

a

Command Line

Evaluation

491

(Conditional Expressions)

Matching

Pattern

Arithmetic Operators

Implicit Command-Line Shell Programs

495

Continuation

Script

Shell

Script

Chapter Summary

510

quiz

493

494

499

500

A Recursive Shell

501

504

512

Advanced Exercises

514

Chapter 11: The Perl Scripting Language Introduction

Perl

to

518 519

More Information 519

Help

519

perldoc

Terminology Running Syntax Variables

521

Perl Program

a

526

528

Array Variables Hash Variables

529 532

Control Structures if/unless if...else

536

foreach/for last and

533

534 537

if...elsif...else

537 539

next

while/until

Sort

522

524

Scalar Variables

Working

487

492

Arithmetic Evaluation

Exercises

480

492

Expressions

The

Descriptors

486

Evaluates, and Executes getopts: Parses Options 488

String

477

483

eval: Scans,

Logical

Command

477

540

with Files

542

546

Subroutines

547

Regular Expressions Syntax and the

=~

550

Operator

550

517

xxvii

xxx

Contents

Language

Basics

Patterns

622

622

Actions

623

Comments

623

Variables

623

Functions

624

Arithmetic Operators Associative

625

Arrays

626

Control Structures

627

printf

626

629

Examples

gawk Programming getline: Controlling Input

Advanced

646 646

Coprocess: Two-Way I/O 648 Getting Input from a Network 650 651

Chapter Summary Exercises

651

Advanced Exercises

652

Chapter 15: The sed Editor Syntax

653

654 654

Arguments

654

Options

Editor Basics

655

Addresses

655

Instructions

656

Control Structures The Hold

657 658

Space

658

Examples

Chapter Summary Exercises

669

669

PART V

Secure Network Utilities

Chapter 16: The rsync Secure Copy Utility Syntax

674

Arguments Options Notes

674

675 676

More Information

677

671 673

Contents

Examples 677 Using a Trailing Slash (/) on source-file 678 Removing Files 678 Copying Files to and from a Remote System Mirroring a Directory 681 Making Backups 681 Restoring

a

File

Chapter Summary Exercises

680

684 684

685

Chapter 17: The OpenSSH Secure Communication Utilities

687

Introduction How Files

to

688

OpenSSH

OpenSSH Works

689

689

More Information

691

Running the ssh, scp, and sftp OpenSSH Clients Tutorial: Using ssh and scp to Connect to an Clients

691

OpenSSH Server

692

Configuring OpenSSH ssh: Logs In or Executes Commands on a Remote System 698 scp: Copies Files to and from a Remote System sftp:

A Secure FTP Client

~/.ssh/config Authorized

and

Keys:

ssh-agent: Holds

Forwarding Port

Automatic

706

Forwarding

707

Exercises

Login Keys

Your Private

XI1

Chapter Summary

700

/etc/ssh/ssh_config Configuration

Tunneling/Port Forwarding

Files

702 705

706

708

709

Advanced Exercises

PART VI Utilities That

Command Reference

Network Utilities Utilities That

709

Display

and

Manipulate

Programming Tools

Miscellaneous Utilities

716

Standard

Multiplicative

Suffixes

Common

Options

The sample

Utility

Files

714

Display and Alter Status

Utilities That Are

718 718

694

717

715 716

713

711

700

691

xxxi

xxxii

Contents

description of what the utility does 719 721 a file for spelling errors at Executes commands at a specified time 725 standard utilities 729 busybox Implements many bzip2 Compresses or decompresses files 732 sample aspell

Brief

Checks

cal

Displays

cat

Joins

calendar

a

and

734 735

files

displays

737 Changes with file the 739 a chgrp Changes group associated chmod Changes the access mode (permissions) of a file 741 chown Changes the owner of a file and/or the group the file is cd

another working directory

to

associated with cmp comm

Compares

two

cp

748

Compares sorted files

configure Configures cpio

746 files

Copies files Creates

an

cut

archive,

restores

date dd df diff diskutil

characters

Displays

or sets

Converts and

files from

an

archive,

du

or

input lines

the system time and date

copies

a

file

766 769

772

file

Displays

a

791 794

message

Converts TABs to SPACES and SPACES to TABs

file find

finger fmt fsck

ftp gawk

785

Displays and manages Directory Service information GSB 788 Displays information on disk usage by directory hierarchy

expand/unexpand expr

a

Displays disk space usage 775 Displays the differences between two text files 777 Checks, modifies, and repairs local volumes CED 782

and/or echo

copies

763

fields from

ditto Copies files and creates and unpacks archives 63D dmesg Displays kernel messages 787 dscl

or

758

Maintains crontab files Selects

752

automatically

754

directory hierarchy crontab

750

code

source

Evaluates

Displays

an

expression

the classification of

Finds files based

Displays

on

796

798 a

criteria

information about

file

802

804 users

810

Formats text very

simply 812 Checks and repairs a filesystem Transfers files

over a

network

814 819

Searches for and processes patterns in

a

file

825

Contents

gcc GetFilelnfo grep

Compiles C and C++ programs Displays file attributes ©15 831 Searches for

gzip Compresses head

Displays

join Joins

pattern in files

a

the

lines from

files based

two

Terminates

a

process

killall

Terminates

a

process

less In

make man mc

Displays

text

Makes

link

a

files,

856

printers

858

to a

to

Keeps

Displays

Manages files a

Creates

a

od

open otool

paste pax

Renames

Changes

in

a

textual environment

ps renice rm

files

or

on

moves a

the

a

(aka Midnight

priority

file of a

890 command

a

file

command that

887

device

a

892

894

keeps running after

you

Joins corresponding Creates

an

archive,

lines from files

restores

a

file (deletes

a

link)

an

archive,

@©

copies

917 925

926

Copies files and directory hierarchies securely

928 over a

929

Securely copies system

or

913

rsync

network

one or more

files

to or

from

930

Manages several textual windows

896

903

907

Paginates files for printing 915 Formats string and numeric data Displays process status 921 Changes the priority of a process Removes

out

905

files from

Removes directories

screen

log

Dumps the content of a file 897 Opens files, directories, and URLs 0® 901 Displays object, library, and executable files (33$

rmdir

scp

861

886

directory filesystem

directory hierarchy pr

852

879

Numbers lines from Runs

850 time

one or more

plutil Manipulates property list files printf

848

of programs current 869 documentation for utilities 875

Creates

nohup

843

846

screen at a

one

field

a set

mkfs

nl

on a common

name

Displays information about

mkdir

mv

by by

file

Commander)

nice

PID

Controls the launchd daemon