The Linux Command Line - Stellenbosch University

[Pages:537]The Linux Command Line

Second Internet Edition

William E. Shotts, Jr.

A Book

Copyright ?2008-2013, William E. Shotts, Jr.

This work is licensed under the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License. To view a copy of this license, visit the link above or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA.

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This book is part of the project, a site for Linux education and advocacy devoted to helping users of legacy operating systems migrate into the future. You may contact the project at .

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Release History

Version 13.07

Date July 6, 2013

Description Second Internet Edition.

09.12

December 14, 2009 First Internet Edition.

09.11

November 19, 2009 Fourth draft with almost all reviewer feedback incorporated and edited through chapter 37.

09.10

October 3, 2009

Third draft with revised table formatting, partial application of reviewers feedback and edited through chapter 18.

09.08

August 12, 2009

Second draft incorporating the first editing pass.

09.07

July 18, 2009

Completed first draft.

Table of Contents

Introduction....................................................................................................xvi

Why Use The Command Line?.....................................................................................xvi What This Book Is About..............................................................................................xvii Who Should Read This Book.......................................................................................xvii What's In This Book.....................................................................................................xviii How To Read This Book..............................................................................................xviii

Prerequisites............................................................................................................xix Why I Don't Call It "GNU/Linux"...........................................................................xix

Acknowledgments..........................................................................................................xx Your Feedback Is Needed!............................................................................................xx What's New In The Second Internet Edition.................................................................xxi Further Reading............................................................................................................xxi Colophon.......................................................................................................................xxi

Part 1 ? Learning The Shell..............................................................1

1 ? What Is The Shell?.....................................................................................2

Terminal Emulators..........................................................................................................2 Your First Keystrokes......................................................................................................2

Command History.......................................................................................................3 Cursor Movement.......................................................................................................3

A Few Words About Mice And Focus....................................................................3 Try Some Simple Commands..........................................................................................4 Ending A Terminal Session..............................................................................................5

The Console Behind The Curtain..........................................................................5 Summing Up....................................................................................................................5 Further Reading...............................................................................................................6

2 ? Navigation...................................................................................................7

Understanding The File System Tree..............................................................................7 The Current Working Directory........................................................................................7 Listing The Contents Of A Directory................................................................................8 Changing The Current Working Directory.......................................................................9

Absolute Pathnames..................................................................................................9 Relative Pathnames...................................................................................................9 Some Helpful Shortcuts............................................................................................11

Important Facts About Filenames........................................................................11

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Summing Up..................................................................................................................12

3 ? Exploring The System.............................................................................13

More Fun With ls...........................................................................................................13 Options And Arguments............................................................................................14 A Longer Look At Long Format.................................................................................16

Determining A File's Type With file................................................................................17 Viewing File Contents With less....................................................................................17

What Is "Text"?.....................................................................................................17 Less Is More........................................................................................................19 A Guided Tour................................................................................................................19 Symbolic Links...............................................................................................................23 Hard Links.....................................................................................................................24 Summing Up..................................................................................................................24 Further Reading.............................................................................................................24

4 ? Manipulating Files And Directories........................................................25

Wildcards.......................................................................................................................25 Character Ranges................................................................................................27 Wildcards Work In The GUI Too..........................................................................27

mkdir ? Create Directories.............................................................................................28 cp ? Copy Files And Directories....................................................................................28

Useful Options And Examples..................................................................................29 mv ? Move And Rename Files......................................................................................30

Useful Options And Examples..................................................................................30 rm ? Remove Files And Directories...............................................................................31

Useful Options And Examples..................................................................................31 Be Careful With rm!.............................................................................................32

ln ? Create Links............................................................................................................33 Hard Links................................................................................................................33 Symbolic Links..........................................................................................................33

Let's Build A Playground................................................................................................34 Creating Directories..................................................................................................34 Copying Files............................................................................................................34 Moving And Renaming Files.....................................................................................35 Creating Hard Links..................................................................................................37 Creating Symbolic Links...........................................................................................38 Removing Files And Directories...............................................................................39 Creating Symlinks With The GUI.........................................................................40

Summing Up..................................................................................................................41 Further Reading.............................................................................................................41

5 ? Working With Commands........................................................................42

What Exactly Are Commands?......................................................................................42 Identifying Commands...................................................................................................43

type ? Display A Command's Type...........................................................................43 which ? Display An Executable's Location...............................................................43 Getting A Command's Documentation..........................................................................44 help ? Get Help For Shell Builtins............................................................................44 --help ? Display Usage Information..........................................................................45

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man ? Display A Program's Manual Page................................................................45 apropos ? Display Appropriate Commands..............................................................47 whatis ? Display A Very Brief Description Of A Command.......................................47

The Most Brutal Man Page Of Them All..............................................................48 info ? Display A Program's Info Entry.......................................................................48 README And Other Program Documentation Files................................................49 Creating Your Own Commands With alias....................................................................50 Summing Up..................................................................................................................52 Further Reading.............................................................................................................52

6 ? Redirection................................................................................................53

Standard Input, Output, And Error.................................................................................53 Redirecting Standard Output.........................................................................................54 Redirecting Standard Error............................................................................................55

Redirecting Standard Output And Standard Error To One File................................56 Disposing Of Unwanted Output................................................................................57

/dev/null In Unix Culture......................................................................................57 Redirecting Standard Input............................................................................................57

cat ? Concatenate Files............................................................................................57 Pipelines........................................................................................................................59

The Difference Between > and |..........................................................................60 Filters........................................................................................................................61 uniq - Report Or Omit Repeated Lines.....................................................................61 wc ? Print Line, Word, And Byte Counts..................................................................62 grep ? Print Lines Matching A Pattern......................................................................62 head / tail ? Print First / Last Part Of Files................................................................63 tee ? Read From Stdin And Output To Stdout And Files..........................................64 Summing Up..................................................................................................................65

Linux Is About Imagination..................................................................................65

7 ? Seeing The World As The Shell Sees It..................................................67

Expansion......................................................................................................................67 Pathname Expansion...............................................................................................68 Pathname Expansion Of Hidden Files.................................................................69 Tilde Expansion........................................................................................................69 Arithmetic Expansion................................................................................................70 Brace Expansion......................................................................................................71 Parameter Expansion...............................................................................................72 Command Substitution.............................................................................................73

Quoting..........................................................................................................................74 Double Quotes..........................................................................................................75 Single Quotes...........................................................................................................76 Escaping Characters................................................................................................77 Backslash Escape Sequences............................................................................77

Summing Up..................................................................................................................78 Further Reading.............................................................................................................78

8 ? Advanced Keyboard Tricks.....................................................................79

Command Line Editing..................................................................................................79 Cursor Movement.....................................................................................................79

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Modifying Text...........................................................................................................80 Cutting And Pasting (Killing And Yanking) Text........................................................80

The Meta Key......................................................................................................81 Completion....................................................................................................................81

Programmable Completion..................................................................................83 Using History.................................................................................................................83

Searching History.....................................................................................................84 History Expansion.....................................................................................................86

script....................................................................................................................86 Summing Up..................................................................................................................86 Further Reading.............................................................................................................87

9 ? Permissions..............................................................................................88

Owners, Group Members, And Everybody Else............................................................89 Reading, Writing, And Executing...................................................................................90

chmod ? Change File Mode.....................................................................................92 What The Heck Is Octal?.....................................................................................93

Setting File Mode With The GUI...............................................................................95 umask ? Set Default Permissions............................................................................96

Some Special Permissions..................................................................................98 Changing Identities........................................................................................................99

su ? Run A Shell With Substitute User And Group IDs............................................99 sudo ? Execute A Command As Another User.......................................................101

Ubuntu And sudo...............................................................................................101 chown ? Change File Owner And Group................................................................102 chgrp ? Change Group Ownership.........................................................................103 Exercising Our Privileges............................................................................................103 Changing Your Password............................................................................................106 Summing Up................................................................................................................107 Further Reading..........................................................................................................107

10 ? Processes.............................................................................................108

How A Process Works.................................................................................................108 Viewing Processes......................................................................................................109

Viewing Processes Dynamically With top..............................................................111 Controlling Processes.................................................................................................113

Interrupting A Process............................................................................................114 Putting A Process In The Background....................................................................114 Returning A Process To The Foreground...............................................................115 Stopping (Pausing) A Process................................................................................116 Signals.........................................................................................................................117 Sending Signals To Processes With kill.................................................................117 Sending Signals To Multiple Processes With killall................................................120 More Process Related Commands.............................................................................120 Summing Up................................................................................................................121

Part 2 ? Configuration And The Environment.............................123

11 ? The Environment..................................................................................124

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What Is Stored In The Environment?..........................................................................124 Examining The Environment..................................................................................124 Some Interesting Variables.....................................................................................126

How Is The Environment Established?.......................................................................127 What's In A Startup File?........................................................................................128

Modifying The Environment.........................................................................................130 Which Files Should We Modify?.............................................................................130 Text Editors.............................................................................................................130 Using A Text Editor.................................................................................................131 Why Comments Are Important..........................................................................134 Activating Our Changes..........................................................................................135

Summing Up................................................................................................................135 Further Reading..........................................................................................................135

12 ? A Gentle Introduction To vi.................................................................136

Why We Should Learn vi.............................................................................................136 A Little Background ....................................................................................................137 Starting And Stopping vi..............................................................................................137

Compatibility Mode............................................................................................138 Editing Modes..............................................................................................................139

Entering Insert Mode..............................................................................................140 Saving Our Work....................................................................................................140 Moving The Cursor Around.........................................................................................141 Basic Editing................................................................................................................142 Appending Text.......................................................................................................142 Opening A Line.......................................................................................................143 Deleting Text...........................................................................................................144 Cutting, Copying, And Pasting Text........................................................................145 Joining Lines...........................................................................................................147 Search-And-Replace...................................................................................................147 Searching Within A Line..........................................................................................147 Searching The Entire File.......................................................................................147 Global Search-And-Replace...................................................................................148 Editing Multiple Files...................................................................................................150 Switching Between Files.........................................................................................151 Opening Additional Files For Editing......................................................................151 Copying Content From One File Into Another........................................................152 Inserting An Entire File Into Another.......................................................................153 Saving Our Work.........................................................................................................154 Summing Up................................................................................................................155 Further Reading..........................................................................................................155

13 ? Customizing The Prompt.....................................................................156

Anatomy Of A Prompt..................................................................................................156 Trying Some Alternative Prompt Designs....................................................................158 Adding Color................................................................................................................159

Terminal Confusion............................................................................................160 Moving The Cursor......................................................................................................162 Saving The Prompt......................................................................................................163 Summing Up................................................................................................................164

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Further Reading..........................................................................................................164

Part 3 ? Common Tasks And Essential Tools.............................165

14 ? Package Management..........................................................................166

Packaging Systems.....................................................................................................166 How A Package System Works...................................................................................167

Package Files.........................................................................................................167 Repositories............................................................................................................167 Dependencies.........................................................................................................168 High And Low-level Package Tools........................................................................168 Common Package Management Tasks.......................................................................169 Finding A Package In A Repository........................................................................169 Installing A Package From A Repository.................................................................169 Installing A Package From A Package File.............................................................170 Removing A Package.............................................................................................170 Updating Packages From A Repository..................................................................171 Upgrading A Package From A Package File...........................................................171 Listing Installed Packages......................................................................................172 Determining If A Package Is Installed.....................................................................172 Displaying Info About An Installed Package...........................................................173 Finding Which Package Installed A File.................................................................173 Summing Up................................................................................................................173

The Linux Software Installation Myth.................................................................174 Further Reading..........................................................................................................175

15 ? Storage Media.......................................................................................176

Mounting And Unmounting Storage Devices..............................................................176 Viewing A List Of Mounted File Systems................................................................178 Why Unmounting Is Important...........................................................................181 Determining Device Names....................................................................................182

Creating New File Systems.........................................................................................185 Manipulating Partitions With fdisk..........................................................................185 Creating A New File System With mkfs..................................................................188

Testing And Repairing File Systems............................................................................189 What The fsck?..................................................................................................189

Formatting Floppy Disks..............................................................................................189 Moving Data Directly To/From Devices.......................................................................190 Creating CD-ROM Images..........................................................................................191

Creating An Image Copy Of A CD-ROM.................................................................191 Creating An Image From A Collection Of Files.......................................................191

A Program By Any Other Name.........................................................................192 Writing CD-ROM Images.............................................................................................192

Mounting An ISO Image Directly............................................................................192 Blanking A Re-Writable CD-ROM...........................................................................193 Writing An Image....................................................................................................193 Summing Up................................................................................................................193 Further Reading..........................................................................................................193 Extra Credit..................................................................................................................193

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