book

A Practical Guide to Linux® Commands, Editors, and Shell Programming

Name: A Practical Guide to Linux® Commands, Editors, and Shell Programming
Author: Mark G. Sobell
ISBN: 0131478230

by Mark G. Sobell

July 2005

Intermediate to advanced

1008 pages

22h 14m

English

Pearson

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Copyright
Dedication
Praise for Mark Sobell's Books
Preface
Command line interface (CLI)Linux distributionsOverlapAudienceBenefitsFeatures Of This BookContentsPart I: The Linux Operating SystemPart II: The EditorsPart III: The ShellsPart IV: Programming ToolsPart V: Command ReferencePart VI: AppendixesSupplementsThanks
1. Welcome to Linux
Free beerThe Gnu–Linux ConnectionThe History of Gnu–LinuxFade to 1983Next Scene, 1991The Code is FreeMINIXGPLHave fun!The Heritage of Linux: UnixWhat is so good about linux?ApplicationsPeripheralsSoftwarePlatformsEmulatorsWhy Linux Is Popular With Hardware Companies And DevelopersProprietary operating systemsGeneric operating systemsLinux Is PortableStandardsThe C Programming LanguageOverview of LinuxLinux Has a Kernel Programming InterfaceLinux Can Support Many UsersLinux Can Run Many TasksLinux Provides a Secure Hierarchical FilesystemStandardsLinksSecurityThe Shell: Command Interpreter And Programming LanguageFilename GenerationDevice-Independent Input And OutputRedirectionShell FunctionsJob ControlA Large Collection Of Useful UtilitiesInterprocess CommunicationPipes and filtersSystem AdministrationAdditional Features of LinuxGuis: Graphical User InterfacesDesktop managerWindow manager(Inter)Networking UtilitiesSoftware DevelopmentChapter SummaryExercises
I. The Linux Operating System
2. Getting Started
Conventions Used in This BookText and examplesItems you enterUtility namesFilenamesCharacter stringsKeys and charactersPrompts and RETURNsDefinitionsURLs (Web addresses)Tip, Caution, and Security boxesLogging InLogging In From a TerminalLogging In Remotely: Terminal Emulation, ssh, and telnetWorking with the ShellWhich Shell Are You Running?Correcting MistakesErasing a CharacterDeleting a WordDeleting a LineAborting ExecutionRepeating/Editing Command LinesCurbing Your Power: Superuser AccessGetting the Facts: Where to Find DocumentationThe ––help Optionman: Displays the System Manualless (pager)Manual sectionsinfo: Displays Information About UtilitiesHOWTOs: Finding Out How Things WorkUsing the Internet to Get HelpGNUThe Linux Documentation ProjectMore About Logging InWhat to Do If You Cannot Log InLogging OutUsing Virtual ConsolesChanging Your PasswordChapter SummaryExercisesAdvanced Exercises
3. Command Line Utilities
Special CharactersWhitespaceBackslashSingle quotation marksBasic Utilitiesls: Lists the Names of Filescat: Displays a Text Filerm: Deletes a Fileless Is more: Displaying a Text File One Screen at a TimePagershostname: Displays the System NameWorking with Filescp: Copies a Filemv: Changes the Name of a Filelpr: Prints a Filegrep: Finds a Stringhead: Displays the Beginning of a Filetail: Displays the End of a Filesort: Displays a File in Orderuniq: Removes Duplicate Lines from a Filediff: Compares Two Filesfile: Tests the Contents of a File| (Pipe): Communicates Between ProcessesFour More Utilitiesecho: Displays Textdate: Displays the Time and Datescript: Records a Linux Sessionunix2dos: Converts Linux Files to Windows Formatdos2unixCompressing and Archiving Filesbzip2: Compresses a File.bz2 filename extensionbunzip2 and bzcat: Decompress a Filebzip2recovergzip: Compresses a Filegunzip and zcatcompresstar: Packs and Unpacks FilesLocating Commandswhich and whereis: Locate a Utilitywhichwhereisapropos: Searches for a Keywordwhatisslocate: Searches for a FileObtaining User and System Informationwho: Lists Users on the Systemfinger: Lists Users on the System.plan and .projectw: Lists Users on the SystemCommunicating with Other Userswrite: Sends a Messagemesg: Denies or Accepts MessagesEmailNetwork addressesChapter SummaryExercisesAdvanced Exercises
4. The Linux Filesystem
The Hierarchical FilesystemFamily treeDirectory treeSubdirectoriesDirectory and Ordinary FilesFilenames/ or rootFilename lengthFilename ExtensionsInvisible Filenamesmkdir:Creates a DirectoryThe working directorypwdSignificance of the Working DirectoryHome Directorycd: Changes to Another Working DirectoryStartup filesAbsolute PathnamesRelative PathnamesThe . and .. Directory entriesImportant Standard Directories and FilesWorking with Directoriesrmdir: Deletes a directoryPathnamestouch~ (Tilde) in pathnamesmv, cp: Moves or Copies a Filemv: Moves a DirectoryAccess Permissionsls –l: Displays Permissionschmod: Changes Access PermissionsSetuid and setgid permissionsDirectory access permissionsLinksSYMBOLIC LINKSLimitations of hard linksln: Creates a Symbolic Linkrm: Removes a LinkChapter summaryExercisesADVANCED EXERCISES
5. The Shell
The Command LineSyntaxCommand NameUsage messageArgumentsOptionsCombining optionsOption argumentsArguments that start with a hyphenProcessing the Command LineParsing the command lineAbsolute versus relative pathnamesExecuting the Command LineProcessThe shell does not process argumentsStandard Input and Standard OutputThe Screen as a FileThe Keyboard and Screen as Standard Input and Standard OutputcatCONTROL-D signals EOFRedirectionRedirecting Standard OutputRedirecting Standard InputUtilities that take input from a file or standard inputnoclobber: Avoids Overwriting FilesAppending Standard Output to a File/dev/null: Making Data DisappearPipestrlprFilterstee: Sends Output in Two DirectionsRunning a Program in the BackgroundForegroundJobsJob number, PID numberMoving a Job from the Foreground to the BackgroundCONTROL-Zkill: Aborting A Background JobDetermining a PID number with psFilename Generation/Pathname ExpansionWildcards, globbingThe ? Special CharacterThe * Special CharacterThe [ ] Special CharactersBuiltinsListing bash builtinsListing tcsh builtinsChapter SummaryUtilities and Builtins Introduced in This ChapterExercisesAdvanced Exercises
II. The Editors

6. The vim Editor
Historyvi clonesWhat vim is notReading this chapterTutorial: Creating and Editing a File with vimvimtutorSpecifying a terminalStarting vimCommand and Input ModesLast Line modevim is case sensitiveEntering TextInput mode (i/a)Getting HelpCorrecting Text as You Insert ItMoving the CursorDeleting TextDelete character (x) Delete word (dw) Delete line (dd)Undoing MistakesUndo (u)Redo (:redo)Entering Additional TextInsert (i) Append (a)Open (o and O)Correcting TextEnding the Editing SessionThe compatible ParameterIntroduction to vim FeaturesOnline HelpModes of OperationThe DisplayStatus LineRedrawing the ScreenTilde (~) SymbolCorrecting Text as You Insert ItWork BufferLine Length and File SizeWindowsFile LocksAbnormal Termination of an Editing SessionRecovering Text After a CrashCommand Mode: Moving the CursorLong linesMoving the Cursor by Charactersl/hMoving the Cursor to a Specific Characterf/FMoving the Cursor by Wordsw/Wb/BMoving the Cursor by Linesj/kMoving the Cursor by Sentences and Paragraphs)/( }/{Moving the Cursor Within the ScreenH/M/LViewing Different Parts of the Work BufferCONTROL-D CONTROL-UCONTROL-F CONTROL-BLine numbers (G)Input ModeInserting TextInsert (i/I)Appending TextAppend (a/A)Opening a Line for TextOpen (o/O)Replacing TextReplace (r/R)Quoting Special Characters in Input ModeCONTROL-VCommand Mode: Deleting and Changing TextUndoing ChangesUndo (u/U)Deleting CharactersDelete character (x/X)Deleting TextDelete (d/D)Changing TextChange (c/C)Replacing TextSubstitute (s/S)Changing CaseSearching and SubstitutingSearching for a CharacterFind (f/F)t/TSearching for a StringNormal Versus Incremental SearchesSpecial Characters in Search Strings^ Beginning-of-Line Indicator$ End-of-Line Indicator. Any-Character Indicator\ > End-of-Word Indicator\ < Beginning-of-Word Indicator* Zero or More Occurrences[ ] Character-Class DefinitionSubstituting One String for AnotherThe Substitute AddressSearching for and Replacing StringsMiscellaneous CommandsJoinJoin (J)StatusStatus (CONTROL-G). (Period).Yank, Put, and Delete CommandsThe General-Purpose BufferCopying Text to the BufferYank (y/Y)Copying Text From the BufferPut (p/P)Deleting Text Copies It into the BufferReading and Writing FilesExit (ZZ)Reading FilesRead (:r)Writing FilesWrite (:w)w!Identifying the Current FileSetting ParametersSetting Parameters from Within vimSetting Parameters in a Startup FileVIMINITThe .vimrc Startup FileParametersAdvanced Editing TechniquesExecuting Shell Commands from Within vimUnits of MeasureCharacterWordBlank-Delimited WordLineSentenceParagraphWindowRepeat FactorChapter SummaryExercisesAdvanced Exercises
7. The emacs Editor
HistoryEvolutionemacs Versus vimTutorial: Getting Started with emacsStarting emacsStopping emacsInserting TextDeleting CharactersMoving the CursorMoving the Cursor by CharactersCONTROL-FCONTROL-BMoving the Cursor by WordsMETA-fMETA-bMoving the Cursor by LinesCONTROL-A CONTROL-E CONTROL-P CONTROL-NMoving the Cursor by Sentences, Paragraphs, and Window PositionMETA-a, META-e META-{, META-}META-rEditing at the Cursor PositionDeleting textSaving and Retrieving the BufferBackupsSaving the bufferVisiting another fileBasic Editing CommandsKeys: Notation and UseKey Sequences and CommandsMETA-x: Running a Command Without a Key BindingSmart completionNumeric ArgumentsCONTROL-UPoint and the CursorScrolling Through a BufferCONTROL-V META-v CONTROL-LMETA-<META->Erasing TextDelete versus killSearchingIncremental SearchesCONTROL-S CONTROL-RNonincremental SearchesCONTROL-S RETURN CONTROL-R RETURNRegular Expression SearchesOnline HelpAdvanced EditingUndoing ChangesMark and RegionMoving Mark and Establishing a RegionCONTROL-@ CONTROL-SPACE CONTROL-X CONTROL-XOperating on a RegionThe Mark RingCONTROL-U CONTROL-@Setting Mark AutomaticallyCut and Paste: Yanking Killed TextInserting Special CharactersGlobal Buffer CommandsLine-Oriented OperationsUnconditional and Interactive ReplacementFilesMETA-x pwd META-x cdVisiting FilesSaving FilesBuffersWindowsSplitting a WindowManipulating WindowsCONTROL-X o META-CONTROL-VOther-Window DisplayCONTROL-X 4b CONTROL-X 4fAdjusting and Deleting WindowsCONTROL-X 0 CONTROL-X 1META-x shrink-window CONTROL-X ^ CONTROL-X } CONTROL-X {Foreground Shell CommandsBackground Shell CommandsMETA-x compileLanguage-Sensitive EditingSelecting a Major ModeMETA-x modenameHuman-Language ModesWordsSentencesParagraphsFillCase ConversionText ModeC ModeExpressionsFunction DefinitionsIndentionCustomizing IndentionCommentsSpecial-Purpose ModesShell ModeMore InformationAccess to emacsChapter SummaryExercisesAdvanced Exercises
III. THE SHELLS
8. The Bourne Again Shell
Backgroundsh ShellKorn ShellPOSIX standardsShell BasicsStartup FilesLogin Shells/etc/profile.bash_profile .bash_login .profile.bash_logoutInteractive Nonlogin Shells/etc/bashrc.bashrcNoninteractive ShellsBASH_ENVSetting Up Startup Files. (Dot) OR source: Runs a Startup File in the Current ShellCommands That Are SymbolsRedirecting Standard ErrorFile descriptorsDuplicating a file descriptorSending errors to standard errorWriting a Simple Shell Scriptchmod: Makes a File Executable#! Specifies a Shell# Begins A CommentRunning A Shell Scriptfork and exec system callsSeparating and Grouping Commands; AND NEWLINE Separate CommandsWhitespace\ Continues a Command| AND & Separate Commands and Do Something ElseJob Controljobs: Lists Jobsfg: Brings a Job to the Foregroundbg: Sends a Job to the BackgroundManipulating the Directory Stackdirs: Displays the Stackpushd: Pushes a Directory on the Stackpopd: Pops a Directory Off the StackParameters and VariablesVariablesUser-created variablesKeyword variablesPositional parameters Special parametersUser-Created VariablesQuoting the $SPACEsPathname expansion in assignmentsunset: Removes a VariableVariable Attributesreadonly: Makes the Value of a Variable Permanentdeclare AND typeset: Assign Attributes to VariablesListing variable attributesIntegerKeyword VariablesHOME: Your Home DirectoryTilde (~)PATH: Where the Shell Looks for ProgramsWorking directoryMAIL: Where Your Mail Is KeptPS1: User Prompt (Primary)PS2: User Prompt (Secondary)PS3: Menu PromptPS4: Debugging PromptIFS: Separates Input Fields (Word Splitting)CDPATH: Broadens the Scope of cdKeyword Variables: A SummarySpecial CharactersProcessesProcess Structurefork system callProcess IdentificationPID numberExecuting A Commandfork and sleepBackground processBuiltinsVariablesHistoryVariables That Control HistoryEvent numberReexecuting and Editing Commandsfc: Displays, Edits, and Reexecutes CommandsViewing the History ListEditing and Reexecuting Previous CommandsReexecuting Commands Without Calling the EditorUsing an Exclamation Point (!) to Reference EventsEvent Designators!! reexecutes the previous event!n event number!string event textThe Readline Libraryvi modeemacs modevi Editing Modeemacs Editing ModeReadline Completion CommandsCommand CompletionPathname CompletionVariable Completion.inputrc: Configuring ReadlineVariablesKey BindingsbindConditional ConstructsAliasesSingle Versus Double Quotation Marks in AliasesExamples of AliasesFunctionsFunctions in startup filesControlling bash Features and OptionsCommand Line OptionsShell Featuresset ±o: Turns Shell Features On and Offshopt: Turns Shell Features On and OffProcessing The Command LineHistory ExpansionAlias SubstitutionParsing and Scanning the Command LineCommand Line ExpansionQuote removalOrder of ExpansionBrace ExpansionTilde ExpansionParameter and Variable ExpansionArithmetic Expansionlet builtinCommand SubstitutionWord SplittingPathname ExpansionQuotation marksLevels of expansionProcess SubstitutionChapter SummaryRunning a shell scriptJob controlVariablesProcessHistoryCommand line editorsAliasesFunctionsShell featuresCommand line expansionExercisesAdvanced Exercises
9. The Tc Shell
Assignment statementShell ScriptsEntering and Leaving the TC ShellchshStartup Files/etc/csh.cshrc and /etc/csh.login.tcshrc and .cshrc.history.login/etc/csh.logout and .logoutFeatures Common to the Bourne Again and TC ShellsCommand Line Expansion (Substitution)Historyhistory BuiltinHistory ExpansionVariableshistory and savehisthistlitAliasesSpecial AliasesHistory Substitution In AliasesJob ControlFilename SubstitutionManipulating the Directory StackCommand SubstitutionRedirecting Standard ErrorWorking with the Command LineWord CompletionFilename CompletionTilde CompletionCommand and Variable CompletionEditing the Command LinebindkeyCorrecting Spellingbefore you press returnAfter You Press ReturnVariablesVariable nameVariable SubstitutionString VariablesArrays of String VariablesNumeric VariablesExpressionsPostincrement and postdecrement operatorsArrays of Numeric VariablesBracesSpecial Variable FormsReading User InputShell VariablesShell Variables That Take On ValuesShell Variables That Act as SwitchesControl StructuresifgotoInterrupt Handlingif...then...elseforeachwhilebreak and continueswitchBuiltinsChapter SummarysetenvAliasesGlobbingExercisesAdvanced Exercises
IV. Programming Tools
10. Programming Tools
Programming In CChecking Your CompilerA C Programming ExampleSymbolic constantsMacrosHeaders (include files)Function prototypeFunctionsCompiling and Linking a C ProgramELF formatUsing Shared LibrariesArchived librarieslddFixing Broken BinariesWrappersCreating Shared LibrariesC+ +make: Keeps a Set of Programs CurrentDependency lines: target files and prerequisite filesImplied Dependenciestouch–n–t–jDebugging C Programsgcc: Compiler Warning OptionsSymbolic DebuggerCore dumpsgdb: Symbolic DebuggerGraphical Symbolic DebuggersThreadsSystem Callsstrace: Traces System CallsControlling ProcessesAccessing The FilesystemSource Code ManagementCVS: Concurrent Versions SystemBuilt-In CVS HelpHow CVS Stores Revision FilesBasic Cvs CommandsChecking Out Files from the Source RepositoryMaking Your Changes Available to OthersUpdating Your Copies with Changes by OthersAdding New Files to the RepositoryRemoving Files from the RepositoryOther CVS CommandsTagging a ReleaseExtracting a ReleaseRemoving Working FilesAdding a Module to the RepositoryCVS AdministrationUsing TkCVSChapter SummarygccgdbmakeExercisesAdvanced Exercises
11. Programming The Bourne Again Shell
Control Structuresif...thentest builtinBuiltinsChecking arguments[] is a synonym for testUsage messageif...then...elseif...then...elifDebugging Shell Scriptsfor...inforwhiletest builtinuntiltrap builtinbreak AND continuecaseselectPS3Here DocumentFile DescriptorsOpening a file descriptorDuplicating a file descriptorParameters And VariablesArray VariablesLocality of VariablesFunctionsFunction local variablesSpecial Parameters$$: PID Number$!$?: Exit StatusPositional Parameters$#: Number of Command Line Arguments$0: Name of the Calling Program$1 – $n: Command Line Arguments$*"$*" versus "$@"shift: Promotes Command Line Argumentsset: Initializes Command Line ArgumentsExpanding Null and Unset Variables: – Uses a Default Value:= Assigns a Default Value: builtin:? Displays An Error MessageBuiltin Commandstype: Displays Information About a Commandread: Accepts User InputREPLYexec: Executes a Commandexec versus . (dot)exec runs a commandexec does not return controlexec redirects input and output/dev/ttytrap: Catches a Signal: (null) builtinkill: Aborts a Processgetopts: Parses OptionsA Partial List of BuiltinsExpressionsArithmetic EvaluationLogical expressionsLogical Evaluation (Conditional Expressions)String comparisonsString Pattern MatchingOperatorsPipeIncrement and decrement operatorsRemainderBooleanTernaryAssignmentOther basesShell ProgramsA Recursive Shell ScriptmakepathThe quiz Shell ScriptquizChapter SummaryControl structuresFile descriptorsVariablesBuiltinsUtilities in scriptsExpressionsExercisesAdvanced Exercises
12. The gawk Pattern Processing Language
SyntaxArgumentsOptions– –field-separator fs– –file program-file– –assign var =valueNotesLanguage BasicsPatternsBEGIN and END, (comma)ActionsCommentsVariablesFunctionsArithmetic OperatorsAssociative ArraysprintfControl Structuresif...elsewhileforbreakcontinueExamplescars data fileMissing patternMissing actionSingle quotation marksFields~ (matches operator)Dollar signsTextual comparisons, (range operator)– –file optionBEGINlength functionNR (record number)ENDStand-alone scriptOFS variableprintfRedirecting outputAssociative arraysError MessagesChapter SummaryExercisesAdvanced Exercises
13. The sed Editor
SyntaxArgumentsOptionsEditor BasicsAddressesInstructionsControl StructuresBranch instructionsThe Pattern Space and the Hold SpaceExamplesprogram-fileAppendInsertChangeSubstituteStand-alone scriptHold spaceChapter SummaryExercises
V. Command Reference
Command Reference
Utilities That Display and Manipulate FilesNetwork UtilitiesUtilities That Display and Alter StatusUtilities That Are Programming ToolsMiscellaneous UtilitiesStandard Multiplicative SuffixesCommon OptionsThe sample Utilitysample: Very brief description of what the utility doesArgumentsOptions––delimiter=dcharDiscussionNotesExamplesaspell: Checks a file for spelling errorsActionArgumentsOptionsDiscussionNotesSpelling from emacsSpelling from vimExamplesat: Executes commands at a specified timeArgumentsOptionsNotes/etc/at.allow and /etc/at.denyExamplesbzip2: Compresses or decompresses filesArgumentsOptionsDiscussionNotesbzcat file-listbzip2recoverExamplescal: Displays a calendarArgumentsOptionsNotesExamplescat: Joins and displays filesArgumentsOptions––number-nonblank––show-nonprintingNotesExamplescd: Changes to another working directoryArgumentsNotesExampleschgrp: Changes the group associated with a fileArgumentsOptions––no-dereference––reference=rfileNotesExampleschmod: Changes the access mode (permissions) of a fileArgumentsSymbolicAbsoluteOptions––reference=rfileNotesExampleschown: Changes the owner of a file and/or the group the file is associated withArgumentsOptions––no-dereference––reference=rfileNotesExamplescmp: Compares two filesArgumentsOptionsNotesExamplescomm: Compares sorted filesArgumentsOptionsNotesExamplesconfigure: Configures source code automaticallyOptions––disable-feature––enable-feature––prefix=directoryDiscussionNotesExamplescp: Copies filesArgumentsOptions––no-dereference––preserve=linksNotesExamplescpio: Creates an archive or restores files from an archiveArgumentsOptionsMajor OptionsOther Options––reset–access–time––make–directories––pattern–file=filename––preserve–modification–time––no-absolute-filenamesDiscussionExamplescrontab: Maintains crontab filesArgumentsOptionsNotes/etc/cron.allow /etc/cron.denyExamplescut: Selects characters or fields from input linesArgumentsOptionsNotesExamplesdate: Displays or sets the system time and dateArgumentsSetting the dateOptionsNotesExamplesdd: Converts and copies a fileArgumentsNotesExamplesWiping a fileCopying a diskettedf: Displays disk space usageArgumentsOptionsExamplesdiff: Displays the differences between two filesArgumentsOptionsNotesDiscussionExamplesContext diffdu: Displays information on disk usage by fileArgumentsOptionsExamplesecho: Displays a messageArgumentsOptionsNotesExamplesexpr: Evaluates an expressionArgumentsNotesExamplesfile: Displays the classification of a fileArgumentsOptionsNotesExamplesfind: Finds files based on criteriaArgumentsCriteriaDiscussionAction criteriaNotesExamplesfinger: Displays information about usersArgumentsOptionsDiscussionNotesExamplesfmt: Formats text very simplyArgumentsOptionsNotesExamplesfsck: Checks and repairs a filesystemArgumentsOptionsGlobal OptionsFilesystem Type-Specific OptionsNotesInteractive modeOrder of checkingfsck is a front endBoot timelost+foundMessagesCleanupftp: Transfers files over a networkArgumentsOptionsDiscussionNotesAnonymous FTPPassive versus active connectionsAutomatic loginExamplesConnect and log inls and cdget and putTimeout and openlcd (local cd)mget and promptgcc: Compiles C and C++ programsArgumentsOptionsNotesExamplesgrep: Searches for a pattern in filesArgumentsOptionsMajor OptionsOther OptionsNotesegrep and fgrepExamplesgzip: Compresses or decompresses filesArgumentsOptionsDiscussionNotesExampleshead: Displays the beginning of a fileArgumentsOptionsNotesExampleskill: Terminates a process by PIDArgumentsOptionsNotesExampleskillall: Terminates a process by nameArgumentsOptionsNotesExamplesless: Displays text files, one screen at a timeArgumentsOptionsNotesCommandsExamplesln: Makes a link to a fileArgumentsOptionsNotesHard linksSymbolic linksExampleslpr: Sends files to printersArgumentsOptionsDiscussionlpqlprmNotesLPD and LPRCUPSExamplesls: Displays information about one or more filesArgumentsOptionsDiscussionNotesExamplesmake: Keeps a set of programs currentArgumentsOptionsDiscussionDocumentationNotesExamplesman: Displays documentation for commandsArgumentsOptionsDiscussionPagerMANPATHNotesExamplesmkdir: Creates a directoryArgumentsOptionsNotesExamplesmkfs: Creates a filesystem on a deviceArgumentsOptionsGlobal OptionsFilesystem Type-Specific OptionsDiscussionNotesmkfs is a front endExamplesMtools: Uses DOS-style commands on files and directoriesUtilitiesArgumentsOptionsmcopymdirmformatmtypeDiscussionNotesExamplesmv: Renames or moves a fileArgumentsOptionsNotesExamplesnice: Changes the priority of a commandArgumentsOptions––adjustment=valueNotesExamplesnohup: Runs a command that keeps running after you log outArgumentsNotesExamplesod: Dumps the contents of a fileArgumentsOptions––address–radix=baseNotesExamplespaste: Joins corresponding lines from filesArgumentsOptions––delimiter=dlistNotesExamplespr: Paginates files for printingArgumentsOptions––show-control-chars––number-lines=[c[num]]––firstpage[:lastpage]NotesExamplesps: Displays process statusArgumentsOptions––User=usernameDiscussionNotesExamplesps and killrcp: Copies one or more files to or from a remote systemArgumentsOptionsNotesExamplesrlogin: Logs in on a remote systemArgumentsOptionsNotesExamples~/.rhosts filerm: Removes a file (deletes a link)ArgumentsOptionsNotesExamplesrmdir: Removes a directoryArgumentsOptions–– ignore-fail-on-non-emptyNotesExamplesrsh: Executes commands on a remote systemArgumentsOptionsNotesExamplesscp: Securely copies one or more files to or from a remote systemArgumentsOptionsNotesExamplessleep: Creates a process that sleeps for a specified intervalArgumentsExamplessort: Sorts and/or merges filesArgumentsOptions–– ignore-leading-blanks–– dictionary-order––ignore-nonprinting––key=start[,stop]––output=filename––field-separator=xDiscussionSort fieldLeading blanksOptionsMultiple sort fieldsExamplessplit: Divides a file into sectionsArgumentsOptions––suffix-length=len––numeric-suffixesDiscussionExamplesssh: Securely executes commands on a remote systemArgumentsOptionsNotesOpenSSHMessage on initial connection to a serverExamplesstrings: Displays strings of printable charactersArgumentsOptions––print-file-nameDiscussionExamplesstty: Displays or sets terminal parametersOptions––file=/dev/deviceArgumentsSpecial Keys and CharacteristicsModes of Data TransmissionTreatment of CharactersJob Control ParametersNotesExamplestail: Displays the last part (tail) of a fileArgumentsOptions––bytes=[+]n[u]––sleep-interval=nNotesExamplestar: Stores or retrieves files to/from an archive fileArgumentsOptionsModifiers––blocking-factor=n––ignore-failed-read––one-file-system––tape–length=n––absolute-paths––exclude-from=filenameNotesExamplestee: Copies standard input to standard output and one or more filesArgumentsOptions––ignore-interruptsExamplestelnet: Connects to a remote system over a networkArgumentsOptionsDiscussionopen remote-computerNotesExamplestest: Evaluates an expressionArgumentsNotesExamplestop: Dynamically displays process statusOptionsDiscussionNotesExamplestouch: Changes a file's access and/or modification timeArgumentsOptions––date=datestring––time=mtime or ––time=modifyExamplestr: Replaces specified charactersArgumentsRangesCharacter ClassesOptions––squeeze-repeatsNotesExamplestty: Displays the terminal pathnameArgumentsOptionsNotesExamplestune2fs: Changes parameters on an ext2 or ext3 filesystemArgumentsOptionsDiscussionExamplesumask: Establishes the file-creation permissions maskArgumentsNotesExamplesuniq: Displays unique linesArgumentsOptionsExamplesw: Displays information about system usersArgumentsOptionsDiscussionExampleswc: Displays the number of lines, words, and bytesArgumentsOptions––max-line-lengthNotesExampleswhich: Shows where in PATH a command is locatedArgumentsOptions––read-functionsNotesExampleswho: Displays information about logged-in usersArgumentsOptionsDiscussionNotesExamplesxargs: Converts standard input into command linesArgumentsOptions––replace[=marker]––max–lines[=num]––max–args=num––max–procs=num––no–run–if–emptyDiscussionNotesExamples
VI. Appendixes
A. Regular Expressions
CharactersDelimitersSimple StringsSpecial CharactersPeriodsBracketsAsterisksCarets and Dollar SignsQuoting Special CharactersRulesLongest Match PossibleEmpty Regular ExpressionsBracketing ExpressionsThe Replacement StringAmpersandQuoted DigitExtended Regular ExpressionsAppendix Summary
B. Help
Solving A ProblemFinding Linux-Related InformationDocumentationUseful Linux SitesLinux NewsgroupsMailing ListsWordsSoftwareOffice Suites and Word ProcessorsSpecifying a TerminalTERMLANG
C. Keeping The System Up-To-Date
yum: Updates And Installs PackagesConfiguring yumUsing yumAPT: An Alternative To yumUsing AptINSTALLING AND SETTING UP APTUpdate the local package listCheck the dependency treeUpdate the systemAdding And Removing Individual Packagesapt.conf: Configuring AptAPT sectionRPM sectionBitTorrentPrerequisitesHow Bittorrent WorksUsing Bittorrent
Glossary

Content preview from A Practical Guide to Linux® Commands, Editors, and Shell Programming

Chapter 12. The `gawk` Pattern Processing Language

IN THIS CHAPTER

Associative Arrays 534

Control Structures 535

Examples 537

getline: Controlling Input 554

Coprocess: Two-Way I/O 557

Getting Input from a Network 558

Error Messages 559

The gawk (GNU awk) utility is a pattern-scanning and processing language that searches one or more files to see whether they contain records (usually lines) that match specified patterns. It processes lines by performing actions, such as writing the record to standard output or incrementing a counter, each time it finds a match. As opposed to procedural languages, the gawk language is data driven: You describe the data you want to work with ...

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A Practical Guide to Linux Commands, Editors, and Shell Programming, Fourth Edition

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A Practical Guide to Linux® Commands, Editors, and Shell Programming

by Mark G. Sobell

Chapter 12. The `gawk` Pattern Processing Language

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