book

The Linux Command Line

by William E. Shotts Jr.

January 2012

Beginner

480 pages

17h 46m

English

No Starch Press

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Why Use the Command Line?What This Book Is AboutWho Should Read This BookWhat’s in This BookHow to Read This BookPrerequisites
Terminal EmulatorsYour First KeystrokesCommand HistoryCursor MovementTry Some Simple CommandsEnding a Terminal Session
Understanding the Filesystem TreeThe Current Working DirectoryListing the Contents of a DirectoryChanging the Current Working DirectoryAbsolute PathnamesRelative PathnamesSome Helpful Shortcuts
More Fun with lsOptions and ArgumentsA Longer Look at Long FormatDetermining a File’s Type with fileViewing File Contents with lessA Guided TourSymbolic Links
Wildcardsmkdir—Create Directoriescp—Copy Files and Directoriesmv—Move and Rename Filesrm—Remove Files and Directoriesln—Create LinksHard LinksSymbolic LinksLet’s Build a PlaygroundCreating DirectoriesCopying FilesMoving and Renaming FilesCreating Hard LinksCreating Symbolic LinksRemoving Files and DirectoriesFinal Note
What Exactly Are Commands?Identifying Commandstype—Display a Command’s Typewhich—Display an Executable’s LocationGetting a Command’s Documentationhelp—Get Help for Shell Builtins--help—Display Usage Informationman—Display a Program’s Manual Pageapropos—Display Appropriate Commandswhatis—Display a Very Brief Description of a Commandinfo—Display a Program’s Info EntryREADME and Other Program Documentation FilesCreating Your Own Commands with aliasRevisiting Old Friends

Standard Input, Output, and ErrorRedirecting Standard OutputRedirecting Standard ErrorRedirecting Standard Output and Standard Error to One FileDisposing of Unwanted OutputRedirecting Standard Inputcat—Concatenate FilesPipelinesFiltersuniq—Report or Omit Repeated Lineswc—Print Line, Word, and Byte Countsgrep—Print Lines Matching a Patternhead/tail—Print First/Last Part of Filestee—Read from Stdin and Output to Stdout and FilesFinal Note
ExpansionPathname ExpansionTilde ExpansionArithmetic ExpansionBrace ExpansionParameter ExpansionCommand SubstitutionQuotingDouble QuotesSingle QuotesEscaping CharactersFinal Note
Command Line EditingCursor MovementModifying TextCutting and Pasting (Killing and Yanking) TextCompletionUsing HistorySearching HistoryHistory ExpansionFinal Note
Owners, Group Members, and Everybody ElseReading, Writing, and Executingchmod—Change File ModeOctal RepresentationSymbolic RepresentationSetting File Mode with the GUIumask—Set Default PermissionsChanging Identitiessu—Run a Shell with Substitute User and Group IDssudo—Execute a Command as Another Userchown—Change File Owner and Groupchgrp—Change Group OwnershipExercising Your PrivilegesChanging Your Password
How a Process WorksViewing Processes with psViewing Processes Dynamically with topControlling ProcessesInterrupting a ProcessPutting a Process in the BackgroundReturning a Process to the ForegroundStopping (Pausing) a ProcessSignalsSending Signals to Processes with killSending Signals to Multiple Processes with killallMore Process-Related Commands
What Is Stored in the Environment?Examining the EnvironmentSome Interesting VariablesHow Is the Environment Established?Login and Non-login ShellsWhat’s in a Startup File?Modifying the EnvironmentWhich Files Should We Modify?Text EditorsUsing a Text EditorActivating Our ChangesFinal Note
Why We Should Learn viA Little BackgroundStarting and Stopping viEditing ModesEntering Insert ModeSaving Our WorkMoving the Cursor AroundBasic EditingAppending TextOpening a LineDeleting TextCutting, Copying, and Pasting TextJoining LinesSearch and ReplaceSearching Within a LineSearching the Entire FileGlobal Search and ReplaceEditing Multiple FilesSwitching Between FilesOpening Additional Files for EditingCopying Content from One File into AnotherInserting an Entire File into AnotherSaving Our Work
Anatomy of a PromptTrying Some Alternative Prompt DesignsAdding ColorMoving the CursorSaving the PromptFinal Note
Packaging SystemsHow a Package System WorksPackage FilesRepositoriesDependenciesHigh- and Low-Level Package ToolsCommon Package Management TasksFinding a Package in a RepositoryInstalling a Package from a RepositoryInstalling a Package from a Package FileRemoving a PackageUpdating Packages from a RepositoryUpgrading a Package from a Package FileListing Installed PackagesDetermining Whether a Package Is InstalledDisplaying Information About an Installed PackageFinding Which Package Installed a FileFinal Note
Mounting and Unmounting Storage DevicesViewing a List of Mounted FilesystemsDetermining Device NamesCreating New FilesystemsManipulating Partitions with fdiskCreating a New Filesystem with mkfsTesting and Repairing FilesystemsFormatting Floppy DisksMoving Data Directly to and from DevicesCreating CD-ROM ImagesCreating an Image Copy of a CD-ROMCreating an Image from a Collection of FilesWriting CD-ROM ImagesMounting an ISO Image DirectlyBlanking a Rewritable CD-ROMWriting an ImageExtra Credit
Examining and Monitoring a Networkping—Send a Special Packet to a Network Hosttraceroute—Trace the Path of a Network Packetnetstat—Examine Network Settings and StatisticsTransporting Files over a Networkftp—Transfer Files with the File Transfer Protocollftp—A Better ftpwget—Non-interactive Network DownloaderSecure Communication with Remote Hostsssh—Securely Log in to Remote Computersscp and sftp—Securely Transfer Files
locate—Find Files the Easy Wayfind—Find Files the Hard WayTestsOperatorsActionsPredefined ActionsUser-Defined ActionsImproving EfficiencyA Return to the PlaygroundOptions
Compressing Filesgzip—Compress or Expand Filesbzip2—Higher Compression at the Cost of SpeedArchiving Filestar—Tape Archiving Utilityzip—Package and Compress FilesSynchronizing Files and Directoriesrsync—Remote File and Directory SynchronizationUsing rsync over a Network
What Are Regular Expressions?grep—Search Through TextMetacharacters and LiteralsThe Any CharacterAnchorsBracket Expressions and Character ClassesNegationTraditional Character RangesPOSIX Character ClassesPOSIX Basic vs. Extended Regular ExpressionsAlternationQuantifiers?—Match an Element Zero Times or One Time*—Match an Element Zero or More Times+—Match an Element One or More Times{ }—Match an Element a Specific Number of TimesPutting Regular Expressions to WorkValidating a Phone List with grepFinding Ugly Filenames with findSearching for Files with locateSearching for Text with less and vimFinal Note
Applications of TextDocumentsWeb PagesEmailPrinter OutputProgram Source CodeRevisiting Some Old Friendscat—Concatenate Files and Print on Standard Outputsort—Sort Lines of Text Filesuniq—Report or Omit Repeated LinesSlicing and Dicingcut—Remove Sections from Each Line of Filespaste—Merge Lines of Filesjoin—Join Lines of Two Files on a Common FieldComparing Textcomm—Compare Two Sorted Files Line by Linediff—Compare Files Line by Linepatch—Apply a diff to an OriginalEditing on the Flytr—Transliterate or Delete Characterssed—Stream Editor for Filtering and Transforming Textaspell—Interactive Spell CheckerFinal NoteExtra Credit
Simple Formatting Toolsnl—Number Linesfold—Wrap Each Line to a Specified Lengthfmt—A Simple Text Formatterpr—Format Text for Printingprintf—Format and Print DataDocument Formatting SystemsThe roff Family and TEXgroff—A Document Formatting SystemFinal Note
A Brief History of PrintingPrinting in the Dim TimesCharacter-Based PrintersGraphical PrintersPrinting with LinuxPreparing Files for Printingpr—Convert Text Files for PrintingSending a Print Job to a Printerlpr—Print Files (Berkeley Style)lp—Print Files (System V Style)Another Option: a2psMonitoring and Controlling Print Jobslpstat—Display Print System Statuslpq—Display Printer Queue Statuslprm and cancel—Cancel Print Jobs
What Is Compiling?Are All Programs Compiled?Compiling a C ProgramObtaining the Source CodeExamining the Source TreeBuilding the ProgramInstalling the ProgramFinal Note
What Are Shell Scripts?How to Write a Shell ScriptScript File FormatExecutable PermissionsScript File LocationGood Locations for ScriptsMore Formatting TricksLong Option NamesIndentation and Line ContinuationFinal Note
First Stage: Minimal DocumentSecond Stage: Adding a Little DataVariables and ConstantsCreating Variables and ConstantsAssigning Values to Variables and ConstantsHere DocumentsFinal Note
Shell FunctionsLocal VariablesKeep Scripts RunningFinal Note
Using ifExit StatusUsing testFile ExpressionsString ExpressionsInteger ExpressionsA More Modern Version of test(( ))—Designed for IntegersCombining ExpressionsControl Operators: Another Way to BranchFinal Note
read—Read Values from Standard InputOptionsSeparating Input Fields with IFSValidating InputMenusFinal NoteExtra Credit
LoopingwhileBreaking out of a LoopuntilReading Files with LoopsFinal Note
Syntactic ErrorsMissing QuotesMissing or Unexpected TokensUnanticipated ExpansionsLogical ErrorsDefensive ProgrammingVerifying InputTestingStubsTest CasesDebuggingFinding the Problem AreaTracingExamining Values During ExecutionFinal Note
casePatternsCombining Multiple PatternsFinal Note
Accessing the Command LineDetermining the Number of Argumentsshift—Getting Access to Many ArgumentsSimple ApplicationsUsing Positional Parameters with Shell FunctionsHandling Positional Parameters En MasseA More Complete ApplicationFinal Note
for: Traditional Shell Formfor: C Language FormFinal Note
Parameter ExpansionBasic ParametersExpansions to Manage Empty VariablesExpansions That Return Variable NamesString OperationsArithmetic Evaluation and ExpansionNumber BasesUnary OperatorsSimple ArithmeticAssignmentBit OperationsLogicbc—An Arbitrary-Precision Calculator LanguageUsing bcAn Example ScriptFinal NoteExtra Credit
What Are Arrays?Creating an ArrayAssigning Values to an ArrayAccessing Array ElementsArray OperationsOutputting the Entire Contents of an ArrayDetermining the Number of Array ElementsFinding the Subscripts Used by an ArrayAdding Elements to the End of an ArraySorting an ArrayDeleting an ArrayFinal Note
Group Commands and SubshellsPerforming RedirectionsProcess SubstitutionTrapsAsynchronous ExecutionwaitNamed PipesSetting Up a Named PipeUsing Named PipesFinal Note

Content preview from The Linux Command Line

Chapter 27. Flow Control: Branching with if

In the last chapter, we were presented with a problem. How can we make our report-generator script adapt to the privileges of the user running the script? The solution to this problem will require us to find a way to “change directions” within our script, based on the results of a test. In programming terms, we need the program to branch.

Let’s consider a simple example of logic expressed in pseudocode, a simulation of a computer language intended for human consumption:

X = 5
If X = 5, then:
Say “X equals 5.”
Otherwise:
Say “X is not equal to 5.”

This is an example of a branch. Based on the condition “Does X = 5?” do one thing: “Say ’X equals 5.’” Otherwise do another thing: “Say ’X is not equal to 5.’”