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You've experienced the shiny, point-and-click surface of your Linux computer-now dive below and explore its depths with the power of the command line. The Linux Command Line takes you from your very first terminal keystrokes to writing full programs in Bash, the most popular Linux shell. Along the way you'll learn the timeless skills handed down by generations of gray-bearded, mouse-shunning gurus: file navigation, environment configuration, command chaining, pattern matching with regular expressions, and more. In addition to that practical knowledge, author William Shotts reveals the philosophy behind these tools and the rich heritage that your desktop Linux machine has inherited from Unix supercomputers of yore. As you make your way through the book's short, easily-digestible chapters, you'll learn how to: * Create and delete files, directories, and symlinks * Administer your system, including networking, package installation, and process management * Use standard input and output, redirection, and pipelines * Edit files with Vi, the world's most popular text editor * Write shell scripts to automate common or boring tasks * Slice and dice text files with cut, paste, grep, patch, and sed Once you overcome your initial "shell shock," you'll find that the command line is a natural and expressive way to communicate with your computer. Just don't be surprised if your mouse starts to gather dust.

Part 1 – Introduction.........................................................................1
1 – Introduction................................................................................................2
Why Use The Command Line?.......................................................................................2
What This Book Is About.................................................................................................3
Who Should Read This Book..........................................................................................3
What's In This Book.........................................................................................................4
How To Read This Book..................................................................................................5
Prerequisites...............................................................................................................5
Why I Don't Call It “GNU/Linux”.............................................................................5
Acknowledgments...........................................................................................................6
Your Feedback Is Needed!..............................................................................................7
Further Reading...............................................................................................................7
Colophon.........................................................................................................................7
Part 2 – Learning The Shell..............................................................9
2 – What Is The Shell?...................................................................................10
Terminal Emulators........................................................................................................10
Your First Keystrokes....................................................................................................10
Command History.....................................................................................................11
Cursor Movement.....................................................................................................11
A Few Words About Mice And Focus...................................................................11
Try Some Simple Commands........................................................................................12
Ending A Terminal Session............................................................................................13
The Console Behind The Curtain........................................................................13
Further Reading.............................................................................................................13
3 – Navigation.................................................................................................14
Understanding The File System Tree............................................................................14
The Current Working Directory......................................................................................14
Listing The Contents Of A Directory..............................................................................15
Changing The Current Working Directory.....................................................................16
Absolute Pathnames................................................................................................16
Relative Pathnames.................................................................................................16
Some Helpful Shortcuts............................................................................................18
Important Facts About Filenames........................................................................18
4 – Exploring The System.............................................................................20
More Fun With ls...........................................................................................................20
Options And Arguments............................................................................................21
A Longer Look At Long Format.................................................................................22
Determining A File's Type With file................................................................................23
Viewing File Contents With less....................................................................................24
What Is “Text”?.....................................................................................................24
Less Is More........................................................................................................26
A Guided Tour................................................................................................................26
Symbolic Links...............................................................................................................29
Hard Links.....................................................................................................................30
Further Reading.............................................................................................................30
5 – Manipulating Files And Directories........................................................31
Wildcards.......................................................................................................................31
Character Ranges................................................................................................33
Wildcards Work In The GUI Too..........................................................................33
mkdir – Create Directories.............................................................................................34
cp – Copy Files And Directories....................................................................................34
Useful Options And Examples..................................................................................35
mv – Move And Rename Files......................................................................................36
Useful Options And Examples..................................................................................36
rm – Remove Files And Directories...............................................................................37
Useful Options And Examples..................................................................................37
Be Careful With rm!.............................................................................................38
ln – Create Links............................................................................................................39
Hard Links................................................................................................................39
Symbolic Links..........................................................................................................40
Let's Build A Playground................................................................................................40
Creating Directories..................................................................................................40
Copying Files............................................................................................................41
Moving And Renaming Files.....................................................................................42
Creating Hard Links..................................................................................................43
Creating Symbolic Links...........................................................................................44
Removing Files And Directories...............................................................................45
Creating Symlinks With The GUI.........................................................................47
Summing Up.............................................................................................................47
6 – Working With Commands........................................................................48
What Exactly Are Commands?......................................................................................48
Identifying Commands...................................................................................................49
type – Display A Command's Type...........................................................................49
which – Display An Executable's Location...............................................................49
Getting A Command's Documentation..........................................................................50
help – Get Help For Shell Builtins............................................................................50
--help – Display Usage Information..........................................................................51
man – Display A Program's Manual Page................................................................51
apropos – Display Appropriate Commands..............................................................53
whatis – Display A Very Brief Description Of A Command.......................................53
The Most Brutal Man Page Of Them All..............................................................53
info – Display A Program's Info Entry.......................................................................54
README And Other Program Documentation Files................................................55
Creating Your Own Commands With alias....................................................................56
Revisiting Old Friends...................................................................................................58
Further Reading.............................................................................................................58
7 – Redirection................................................................................................59
Standard Input, Output, And Error.................................................................................59
Redirecting Standard Output.........................................................................................60
Redirecting Standard Error............................................................................................61
Redirecting Standard Output And Standard Error To One File................................62
Disposing Of Unwanted Output................................................................................63
/dev/null In Unix Culture......................................................................................63
Redirecting Standard Input............................................................................................63
cat – Concatenate Files............................................................................................63
Pipelines........................................................................................................................65
Filters........................................................................................................................66
uniq - Report Or Omit Repeated Lines....................................................................66
wc – Print Line, Word, And Byte Counts..................................................................67
grep – Print Lines Matching A Pattern......................................................................67
head / tail – Print First / Last Part Of Files................................................................68
tee – Read From Stdin And Output To Stdout And Files..........................................69
Summing Up..................................................................................................................70
Linux Is About Imagination..................................................................................70
8 – Seeing The World As The Shell Sees It..................................................72
Expansion......................................................................................................................72
Pathname Expansion...............................................................................................73
Pathname Expansion Of Hidden Files.................................................................74
Tilde Expansion........................................................................................................74
Arithmetic Expansion................................................................................................75
Brace Expansion......................................................................................................76
Parameter Expansion...............................................................................................77
Command Substitution.............................................................................................78
Quoting..........................................................................................................................79
Double Quotes..........................................................................................................79
Single Quotes...........................................................................................................81
Escaping Characters................................................................................................82
Backslash Escape Sequences............................................................................82
Summing Up..................................................................................................................83
Further Reading.............................................................................................................83
9 – Advanced Keyboard Tricks.....................................................................84
Command Line Editing..................................................................................................84
Cursor Movement.....................................................................................................84
Modifying Text...........................................................................................................85
Cutting And Pasting (Killing And Yanking) Text........................................................85
The Meta Key......................................................................................................86
Completion....................................................................................................................86
Programmable Completion..................................................................................88
Using History.................................................................................................................88
Searching History.....................................................................................................89
History Expansion.....................................................................................................91
script....................................................................................................................91
Summing Up..................................................................................................................92
Further Reading.............................................................................................................92
10 – Permissions............................................................................................93
Owners, Group Members, And Everybody Else............................................................94
Reading, Writing, And Executing...................................................................................95
chmod – Change file mode.......................................................................................97
What The Heck Is Octal?.....................................................................................98
Setting File Mode With The GUI.............................................................................100
umask – Set Default Permissions..........................................................................101
Some Special Permissions................................................................................103
Changing Identities......................................................................................................104
su – Run A Shell With Substitute User And Group IDs..........................................105
sudo – Execute A Command As Another User.......................................................106
Ubuntu And sudo...............................................................................................107
chown – Change File Owner And Group................................................................107
chgrp – Change Group Ownership.........................................................................109
Exercising Our Privileges............................................................................................109
Changing Your Password.............................................................................................111
Further Reading...........................................................................................................112
11 – Processes..............................................................................................113
How A Process Works.................................................................................................113
Viewing Processes......................................................................................................114
Viewing Processes Dynamically With top...............................................................116
Controlling Processes..................................................................................................118
Interrupting A Process.............................................................................................119
Putting A Process In The Background....................................................................119
Returning A Process To The Foreground...............................................................120
Stopping (Pausing) A Process................................................................................121
Signals.........................................................................................................................122
Sending Signals To Processes With kill.................................................................122
Sending Signals To Multiple Processes With killall................................................125
More Process Related Commands.............................................................................125
Part 3 – Configuration And The Environment.............................127
12 – The Environment..................................................................................128
What Is Stored In The Environment?..........................................................................128
Examining The Environment..................................................................................128
Some Interesting Variables.....................................................................................130
How Is The Environment Established?.......................................................................131
What's In A Startup File?........................................................................................132
Modifying The Environment.........................................................................................134
Which Files Should We Modify?.............................................................................134
Text Editors.............................................................................................................134
Using A Text Editor.................................................................................................135
Why Comments Are Important..........................................................................138
Activating Our Changes..........................................................................................139
Summing Up................................................................................................................139
Further Reading..........................................................................................................139
13 – A Gentle Introduction To vi.................................................................140
Why We Should Learn vi.............................................................................................140
A Little Background ....................................................................................................141
Starting And Stopping vi..............................................................................................141
Compatibility Mode............................................................................................142
Editing Modes..............................................................................................................143
Entering Insert Mode..............................................................................................144
Saving Our Work....................................................................................................144
Moving The Cursor Around.........................................................................................145
Basic Editing................................................................................................................146
Appending Text.......................................................................................................146
Opening A Line.......................................................................................................147
Deleting Text...........................................................................................................148
Cutting, Copying And Pasting Text.........................................................................149
Joining Lines...........................................................................................................151
Search And Replace....................................................................................................151
Searching Within A Line..........................................................................................151
Searching The Entire File.......................................................................................151
Global Search And Replace...................................................................................152
Editing Multiple Files...................................................................................................154
Switching Between Files.........................................................................................155
Opening Additional Files For Editing......................................................................155
Copying Content From One File Into Another........................................................156
Inserting An Entire File Into Another.......................................................................157
Saving Our Work.........................................................................................................158
Further Reading..........................................................................................................159
14 – Customizing The Prompt.....................................................................160
Anatomy Of A Prompt..................................................................................................160
Trying Some Alternate Prompt Designs......................................................................162
Adding Color................................................................................................................163
Terminal Confusion............................................................................................163
Moving The Cursor......................................................................................................166
Saving The Prompt......................................................................................................167
Summing Up................................................................................................................167
Further Reading..........................................................................................................168
Part 4 – Common Tasks And Essential Tools.............................169
15 – Package Management..........................................................................170
Packaging Systems.....................................................................................................170
How A Package System Works...................................................................................171
Package Files.........................................................................................................171
Repositories............................................................................................................171
Dependencies.........................................................................................................172
High And Low-level Package Tools........................................................................172
Common Package Management Tasks.......................................................................173
Finding A Package In A Repository........................................................................173
Installing A Package From A Repository.................................................................173
Installing A Package From A Package File.............................................................174
Removing A Package.............................................................................................174
Updating Packages From A Repository..................................................................175
Upgrading A Package From A Package File...........................................................175
Listing Installed Packages......................................................................................176
Determining If A Package Is Installed.....................................................................176
Displaying Info About An Installed Package...........................................................177
Finding Which Package Installed A File.................................................................177
Summing Up................................................................................................................177
The Linux Software Installation Myth.................................................................178
Further Reading..........................................................................................................179
16 – Storage Media.......................................................................................180
Mounting And Unmounting Storage Devices..............................................................180
Viewing A List Of Mounted File Systems................................................................182
Why Unmounting Is Important...........................................................................185
Determining Device Names....................................................................................186
Creating New File Systems.........................................................................................189
Manipulating Partitions With fdisk..........................................................................189
Creating A New File System With mkfs..................................................................192
Testing And Repairing File Systems............................................................................193
What The fsck?..................................................................................................193
Formatting Floppy Disks..............................................................................................193
Moving Data Directly To/From Devices.......................................................................194
Creating CD-ROM Images..........................................................................................195
Creating An Image Copy Of A CD-ROM.................................................................195
Creating An Image From A Collection Of Files.......................................................195
A Program By Any Other Name.........................................................................196
Writing CD-ROM Images.............................................................................................196
Mounting An ISO Image Directly............................................................................196
Blanking A Re-Writable CD-ROM...........................................................................197
Writing An Image....................................................................................................197
Further Reading..........................................................................................................197
Extra Credit..................................................................................................................197
17 – Networking............................................................................................199
Examining And Monitoring A Network.........................................................................200
ping.........................................................................................................................200
traceroute...............................................................................................................201
netstat.....................................................................................................................202
Transporting Files Over A Network..............................................................................203
ftp............................................................................................................................204
lftp – A Better ftp.....................................................................................................206
wget........................................................................................................................206
Secure Communication With Remote Hosts...............................................................206
ssh..........................................................................................................................207
Tunneling With SSH..........................................................................................210
scp And sftp............................................................................................................211
An SSH Client For Windows?............................................................................212
Further Reading..........................................................................................................212
18 – Searching For Files..............................................................................213
locate – Find Files The Easy Way...............................................................................213
Where Does The locate Database Come From?..............................................215
find – Find Files The Hard Way...................................................................................215
Tests.......................................................................................................................216
Operators................................................................................................................218
Predefined Actions..................................................................................................221
User Defined Actions..............................................................................................223
Improving Efficiency...............................................................................................224
xargs.......................................................................................................................224
Dealing With Funny Filenames..........................................................................225
A Return To The Playground..................................................................................226
Options...................................................................................................................228
Further Reading..........................................................................................................229
19 – Archiving And Backup.........................................................................230
Compressing Files.......................................................................................................230
gzip.........................................................................................................................231
bzip2.......................................................................................................................233
Don’t Be Compressive Compulsive...................................................................234
Archiving Files.............................................................................................................234
tar............................................................................................................................234
zip...........................................................................................................................240
Synchronizing Files And Directories............................................................................242
Using rsync Over A Network...................................................................................245
Further Reading..........................................................................................................246
20 – Regular Expressions...........................................................................247
What Are Regular Expressions?............................................................................247
grep.............................................................................................................................247
Metacharacters And Literals........................................................................................249
The Any Character......................................................................................................250
Anchors.......................................................................................................................251
A Crossword Puzzle Helper...............................................................................251
Bracket Expressions And Character Classes..............................................................252
Negation.................................................................................................................252
Traditional Character Ranges.................................................................................253
POSIX Character Classes......................................................................................254
Reverting To Traditional Collation Order............................................................257
POSIX Basic Vs. Extended Regular Expressions.......................................................258
POSIX................................................................................................................258
Alternation...................................................................................................................259
Quantifiers...................................................................................................................260
? - Match An Element Zero Or One Time...............................................................260
* - Match An Element Zero Or More Times............................................................261
+ - Match An Element One Or More Times............................................................262
{ } - Match An Element A Specific Number Of Times..............................................262
Putting Regular Expressions To Work.........................................................................263
Validating A Phone List With grep...........................................................................263
Finding Ugly Filenames With find...........................................................................264
Searching For Files With locate.............................................................................265
Searching For Text In less And vim........................................................................265
Summing Up................................................................................................................267
Further Reading..........................................................................................................267
21 – Text Processing....................................................................................268
Applications Of Text.....................................................................................................268
Documents.............................................................................................................269
Web Pages.............................................................................................................269
Email.......................................................................................................................269
Printer Output.........................................................................................................269
Program Source Code............................................................................................269
Revisiting Some Old Friends.......................................................................................269
cat...........................................................................................................................270
MS-DOS Text Vs. Unix Text...............................................................................271
sort..........................................................................................................................271
uniq.........................................................................................................................279
Slicing And Dicing........................................................................................................280
cut...........................................................................................................................280
Expanding Tabs.................................................................................................283
paste.......................................................................................................................284
join..........................................................................................................................285
Comparing Text...........................................................................................................287
comm......................................................................................................................288
diff...........................................................................................................................288
patch.......................................................................................................................291
Editing On The Fly.......................................................................................................292
tr..............................................................................................................................292
ROT13: The Not-So-Secret Decoder Ring........................................................294
sed..........................................................................................................................295
People Who Like sed Also Like.........................................................................303
aspell......................................................................................................................303
Summing Up................................................................................................................307
Further Reading..........................................................................................................307
Extra Credit..................................................................................................................308
22 – Formatting Output................................................................................309
Simple Formatting Tools..............................................................................................309
nl – Number Lines..................................................................................................309
fold – Wrap Each Line To A Specified Length........................................................313
fmt – A Simple Text Formatter................................................................................313
pr – Format Text For Printing..................................................................................317
printf – Format And Print Data................................................................................318
Document Formatting Systems...................................................................................321
groff.........................................................................................................................322
Summing Up................................................................................................................328
Further Reading..........................................................................................................328
23 – Printing..................................................................................................330
A Brief History Of Printing............................................................................................330
Printing In The Dim Times......................................................................................330
Character-based Printers.......................................................................................331
Graphical Printers...................................................................................................332
Printing With Linux......................................................................................................333
Preparing Files For Printing.........................................................................................333
pr – Convert Text Files For Printing........................................................................333
Sending A Print Job To A Printer..................................................................................335
lpr – Print Files (Berkeley Style).............................................................................335
lp – Print Files (System V Style).............................................................................336
Another Option: a2ps..............................................................................................337
Monitoring And Controlling Print Jobs.........................................................................340
lpstat – Display Print System Status......................................................................340
lpq – Display Printer Queue Status........................................................................341
lprm / cancel – Cancel Print Jobs..........................................................................342
Summing Up................................................................................................................342
Further Reading..........................................................................................................342
24 – Compiling Programs............................................................................344
What Is Compiling?.....................................................................................................344
Are All Programs Compiled?..................................................................................345
Compiling A C Program...............................................................................................346
Obtaining The Source Code...................................................................................346
Examining The Source Tree...................................................................................348
Building The Program.............................................................................................350
Installing The Program...........................................................................................354
Summing Up................................................................................................................354
Further Reading..........................................................................................................355
Part 5 – Writing Shell Scripts.......................................................357
25 – Writing Your First Script......................................................................358
What Are Shell Scripts?...............................................................................................358
How To Write A Shell Script.........................................................................................358
Script File Format........................................................................................................359
Executable Permissions..............................................................................................360
Script File Location......................................................................................................360
Good Locations For Scripts....................................................................................362
More Formatting Tricks................................................................................................362
Long Option Names................................................................................................362
Indentation And Line Continuation.........................................................................362
Configuring vim For Script Writing.....................................................................363
Summing Up................................................................................................................364
Further Reading..........................................................................................................364
26 – Starting A Project.................................................................................365
First Stage: Minimal Document...................................................................................365
Second Stage: Adding A Little Data............................................................................367
Variables And Constants.............................................................................................368
Assigning Values To Variables And Constants.......................................................371
Here Documents.........................................................................................................372
Summing Up................................................................................................................375
Further Reading..........................................................................................................375
27 – Top-Down Design.................................................................................376
Shell Functions............................................................................................................377
Local Variables............................................................................................................380
Keep Scripts Running..................................................................................................381
Shell Functions In Your .bashrc File..................................................................384
Summing Up................................................................................................................384
Further Reading..........................................................................................................384
28 – Flow Control: Branching With if.........................................................385
if...................................................................................................................................385
Exit Status...................................................................................................................386
test...............................................................................................................................388
File Expressions.....................................................................................................388
String Expressions..................................................................................................391
Integer Expressions................................................................................................392
A More Modern Version Of test...................................................................................393
(( )) - Designed For Integers........................................................................................395
Combining Expressions...............................................................................................396
Portability Is The Hobgoblin Of Little Minds.......................................................398
Control Operators: Another Way To Branch................................................................399
Summing Up................................................................................................................399
Further Reading..........................................................................................................400
29 – Reading Keyboard Input......................................................................401
read – Read Values From Standard Input...................................................................402
Options...................................................................................................................404
IFS..........................................................................................................................406
You Can’t Pipe read...........................................................................................407
Validating Input............................................................................................................408
Menus..........................................................................................................................409
Summing Up................................................................................................................411
Extra Credit.............................................................................................................411
Further Reading...........................................................................................................411
30 – Flow Control: Looping With while / until...........................................412
Looping........................................................................................................................412
while........................................................................................................................412
Breaking Out Of A Loop...............................................................................................415
until.........................................................................................................................416
Reading Files With Loops...........................................................................................417
Summing Up................................................................................................................418
Further Reading..........................................................................................................418
31 – Troubleshooting...................................................................................419
Syntactic Errors...........................................................................................................419
Missing Quotes.......................................................................................................420
Missing Or Unexpected Tokens..............................................................................420
Unanticipated Expansions......................................................................................421
Logical Errors .............................................................................................................423
Defensive Programming.........................................................................................423
Verifying Input.........................................................................................................425
Design Is A Function Of Time............................................................................425
Testing.........................................................................................................................425
Test Cases..............................................................................................................426
Debugging...................................................................................................................427
Finding The Problem Area......................................................................................427
Tracing....................................................................................................................427
Examining Values During Execution......................................................................430
Summing Up................................................................................................................430
Further Reading..........................................................................................................431
32 – Flow Control: Branching With case...................................................432
case.............................................................................................................................432
Patterns..................................................................................................................434
Summing Up................................................................................................................436
Further Reading..........................................................................................................436
33 – Positional Parameters.........................................................................437
Accessing The Command Line...................................................................................437
Determining The Number of Arguments.................................................................438
shift – Getting Access To Many Arguments............................................................439
Simple Applications................................................................................................440
Using Positional Parameters With Shell Functions................................................441
Handling Positional Parameters En Masse.................................................................442
A More Complete Application......................................................................................444
Summing Up................................................................................................................447
Further Reading..........................................................................................................450
34 – Flow Control: Looping With for..........................................................451
for: Traditional Shell Form...........................................................................................451
Why i?................................................................................................................453
for: C Language Form.................................................................................................454
Summing Up................................................................................................................455
Further Reading..........................................................................................................456
35 – Strings And Numbers..........................................................................457
Parameter Expansion..................................................................................................457
Basic Parameters...................................................................................................457
Expansions To Manage Empty Variables...............................................................458
Expansions That Return Variable Names..............................................................460
String Operations....................................................................................................460
Arithmetic Evaluation And Expansion.........................................................................463
Number Bases........................................................................................................464
Unary Operators.....................................................................................................464
Simple Arithmetic....................................................................................................464
Assignment.............................................................................................................466
Bit Operations.........................................................................................................468
Logic.......................................................................................................................469
bc – An Arbitrary Precision Calculator Language........................................................472
Using bc..................................................................................................................473
An Example Script..................................................................................................473
Summing Up................................................................................................................475
Extra Credit..................................................................................................................475
Further Reading..........................................................................................................475
36 – Arrays....................................................................................................476
What Are Arrays?........................................................................................................476
Creating An Array........................................................................................................476
Assigning Values To An Array......................................................................................477
Accessing Array Elements...........................................................................................478
Array Operations.........................................................................................................480
Outputting The Entire Contents Of An Array..........................................................480
Determining The Number Of Array Elements.........................................................480
Finding The Subscripts Used By An Array.............................................................481
Adding Elements To The End Of An Array.............................................................481
Sorting An Array......................................................................................................482
Deleting An Array....................................................................................................482
Summing Up................................................................................................................483
Further Reading..........................................................................................................484
37 – Exotica...................................................................................................485
Group Commands And Subshells...............................................................................485
Process Substitution...............................................................................................486
Traps............................................................................................................................488
Temporary Files.................................................................................................491
Asynchronous Execution.............................................................................................492
wait.........................................................................................................................492
Named Pipes...............................................................................................................493
Setting Up A Named Pipe.......................................................................................494
Using Named Pipes................................................................................................494
Summing Up................................................................................................................495
Further Reading..........................................................................................................495
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