The Linux Command Line

Part 1 – Introduction.........................................................................1 更多>>

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