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The Linux Command Line

Third Internet Edition

William Shotts

A LinuxCommand.org Book

A LinuxCommand.org Book

Copyright ©2008-2016, William E. Shotts, Jr.

This work is licensed under the Creative Commons Attribution-Noncommercial-No De- rivative Works 3.0 United States License. To view a copy of this license, visit the link above or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042.

A version of this book is also available in printed form, published by No Starch Press. Copies may be purchased wherever fine books are sold. No Starch Press also offers elec- tronic formats for popular e-readers. They can be reached at: https://www.nostarch.com.

Linux® is the registered trademark of Linus Torvalds. All other trademarks belong to their respective owners.

This book is part of the LinuxCommand.org project, a site for Linux education and advo- cacy devoted to helping users of legacy operating systems migrate into the future. You may contact the LinuxCommand.org project at http://linuxcommand.org.

Release History

Version	Date	Description
16.07	July 28, 2016	Third Internet Edition.
13.07	July 6, 2013	Second Internet Edition.
09.12	December 14, 2009	First Internet Edition.

Introduction Why Use The Command Line?What This Book Is About Who Should Read This Book What's In This Book How To Read This Book Prerequisites Acknowledgments First Internet Edition Second Internet Edition Third Internet Edition Your Feedback Is Needed!What's New In The Third Internet Edition Further Reading Colophon Part 1 – Learning The Shell 1 – What Is The Shell?Terminal Emulators Your First Keystrokes Try Some Simple Commands Ending A Terminal Session Summing Up Further Reading 2 – Navigation Understanding The File System Tree The Current Working Directory Listing The Contents Of A Directory Changing The Current Working Directory Summing Up 3 – Exploring The System More Fun With ls Determining A File's Type With file Viewing File Contents With less A Guided Tour Symbolic Links Hard Links Summing Up Further Reading 4 – Manipulating Files And Directories Wildcards mkdir – Create Directories cp – Copy Files And Directories mv – Move And Rename Files rm – Remove Files And Directories ln – Create Links Let's Build A Playground Summing Up Further Reading 5 – Working With Commands What Exactly Are Commands?Identifying Commands Getting A Command's Documentation Creating Your Own Commands With alias Summing Up Further Reading 6 – Redirection Standard Input, Output, And Error Redirecting Standard Output Redirecting Standard Error Redirecting Standard Input Pipelines Summing Up 7 – Seeing The World As The Shell Sees It Expansion Quoting Summing Up Further Reading 8 – Advanced Keyboard Tricks Command Line Editing Completion Using History Summing Up Further Reading 9 – Permissions Owners, Group Members, And Everybody Else Reading, Writing, And Executing Changing Identities Exercising Our Privileges Changing Your Password Summing Up Further Reading 10 – Processes How A Process Works Viewing Processes Controlling Processes Signals Shutting Down The System More Process Related Commands Summing Up Part 2 – Configuration And The Environment 11 – The Environment What Is Stored In The Environment?How Is The Environment Established?Modifying The Environment Summing Up Further Reading 12 – A Gentle Introduction To vi Why We Should Learn vi A Little Background Starting And Stopping vi Editing Modes Moving The Cursor Around Basic Editing Search-And-Replace Editing Multiple Files Saving Our Work Summing Up Further Reading 13 – Customizing The Prompt Anatomy Of A Prompt Trying Some Alternative Prompt Designs Adding Color Moving The Cursor Saving The Prompt Summing Up Further Reading Part 3 – Common Tasks And Essential Tools 14 – Package Management Packaging Systems How A Package System Works Common Package Management Tasks Summing Up Further Reading 15 – Storage Media Mounting And Unmounting Storage Devices Creating New File Systems Testing And Repairing File Systems Formatting Floppy Disks Moving Data Directly To/From Devices Creating CD-ROM Images Writing CD-ROM Images Summing Up Further Reading Extra Credit 16 – Networking Examining And Monitoring A Network Transporting Files Over A Network Secure Communication With Remote Hosts Summing Up Further Reading 17 – Searching For Files locate – Find Files The Easy Way find – Find Files The Hard Way Summing Up Further Reading 18 – Archiving And Backup Compressing Files Archiving Files Synchronizing Files And Directories Summing Up Further Reading 19 – Regular Expressions What Are Regular Expressions?grep Metacharacters And Literals The Any Character Anchors Bracket Expressions And Character Classes POSIX Basic Vs. Extended Regular Expressions Alternation Quantifiers Putting Regular Expressions To Work Summing Up Further Reading 20 – Text Processing Applications Of Text Revisiting Some Old Friends Slicing And Dicing Comparing Text Editing On The Fly Summing Up Further Reading Extra Credit 21 – Formatting Output Simple Formatting Tools Document Formatting Systems Summing Up Further Reading 22 – Printing A Brief History Of Printing Printing With Linux Preparing Files For Printing Sending A Print Job To A Printer Monitoring And Controlling Print Jobs Summing Up Further Reading 23 – Compiling Programs What Is Compiling?Compiling A C Program Summing Up Further Reading Part 4 – Writing Shell Scripts 24 – Writing Your First Script What Are Shell Scripts?How To Write A Shell Script Script File Format Executable Permissions Script File Location More Formatting Tricks Summing Up Further Reading 25 – Starting A Project First Stage: Minimal Document Second Stage: Adding A Little Data Variables And Constants Here Documents Summing Up Further Reading 26 – Top-Down Design Shell Functions Local Variables Keep Scripts Running Summing Up Further Reading 27 – Flow Control: Branching With if if Exit Status test A More Modern Version Of test (( )) - Designed For Integers Combining Expressions Control Operators: Another Way To Branch Summing Up Further Reading 28 – Reading Keyboard Input read – Read Values From Standard Input Validating Input Menus Summing Up Further Reading 29 – Flow Control: Looping With while / until Looping Breaking Out Of A Loop Reading Files With Loops Summing Up Further Reading 30 – Troubleshooting Syntactic Errors Logical Errors Testing Debugging Summing Up Further Reading 31 – Flow Control: Branching With case case Summing Up Further Reading 32 – Positional Parameters Accessing The Command Line Handling Positional Parameters En Masse A More Complete Application Summing Up Further Reading 33 – Flow Control: Looping With for for: Traditional Shell Form for: C Language Form Summing Up Further Reading 34 – Strings And Numbers Parameter Expansion Arithmetic Evaluation And Expansion bc – An Arbitrary Precision Calculator Language Summing Up Extra Credit Further Reading 35 – Arrays What Are Arrays?Creating An Array Assigning Values To An Array Accessing Array Elements Array Operations Associative Arrays Summing Up Further Reading 36 – Exotica Group Commands And Subshells Traps Asynchronous Execution Named Pipes Summing Up Further Reading Index

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