book

Pro Bash Programming: Scripting the GNU/Linux Shell

by Chris F.A. Johnson

October 2009

Beginner to intermediate

242 pages

5h 4m

English

Apress

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Why the Shell?Just the Shell, Ma'am, Just the ShellA Brief History of shWhich Version of Bash?Who Will Benefit from This Book?What's in the Book?Downloading the CodeContacting the Author
The CodeThe FileChoosing and Using a Text EditorBuilding a Better "Hello, World!"SummaryExercises
Parameter and VariablesArguments and Optionsecho, and Why You Should Avoid Itprintf: Formatting and Printing DataLine ContinuationStandard Input/Output Streams and RedirectionReading InputPipelinesCommand SubstitutionExercises

Exit StatusTesting an ExpressionListsConditional executionLoopingwhileSummaryExercises
QuotingBrace ExpansionTilde ExpansionParameter and Variable ExpansionArithmetic ExpansionCommand SubstitutionWord SplittingPathname ExpansionProcess SubstitutionParsing OptionsSummaryCommandsExercises
The Scope of a Variable: Can You See It from Here?Shell VariablesThe Naming of VariablesParameter ExpansionPositional ParametersArraysSummaryExercises
Definition SyntaxCompound CommandsGetting ResultsFunction LibrariesSample ScriptSummaryExercises
ConcatenationProcessing Character by CharacterCase ConversionComparing Contents Without Regard to CaseCheck for Valid Variable NameInsert One String into AnotherOverlayTrim Unwanted CharactersIndexSummaryExercises
Reading a FileExternal CommandsRegular ExpressionsFile Name Expansion OptionsSummaryShell OptionsExternal CommandsExercises
help, Display Information About Builtin Commandstime, Print Time Taken for Execution of a Commandread, Read a Line from an Input StreamSetting Multiple Variables from One Commandtype, Display Information About Commandsbuiltin, Execute a Builtin Commandcommand, Execute a Command or Display Information About Commandspwd, Print the Current Working DirectoryDeprecated BuiltinsDynamically Loadable BuiltinsSummaryCommands and Reserved WordsExercises
Prevention Is Better Than CureDebugging a ScriptSummaryExercises
Manipulating the Directory StackFilesystem FunctionsMiscellaneous FunctionsManaging Man PagesGamesSummaryExercises
Defining VariablesCommand-Line Options and ArgumentsMenusQ&A DialogueConfiguration FilesScripts with Several NamesEnvironment VariablesAll Together NowSummaryExercises
ArraysData File FormatsSummaryExercises
Teletypewriter vs. CanvasStretching the CanvasPriming the CanvasMoving the CursorChanging Rendition Modes and ColorsPlacing a Block of Text on the ScreenScrolling TextRolling DiceSummaryExercises
Single-Key EntryHistory in ScriptsSanity CheckingForm EntryReading the MouseSummaryExercises
BASHBASHPIDBASH_ALIASESBASH_ARGCBASH_ARGVBASH_CMDSBASH_COMMANDBASH_EXECUTION_STRINGBASH_LINENOBASH_REMATCHBASH_SOURCEBASH_SUBSHELLBASH_VERSINFOBASH_VERSIONCOMP_CWORDCOMP_KEYCOMP_LINECOMP_POINTCOMP_TYPECOMP_WORDBREAKSCOMP_WORDSDIRSTACKEUIDFUNCNAMEGROUPSHISTCMDHOSTNAMEHOSTTYPELINENOMACHTYPEOLDPWDOPTARGOPTINDOSTYPEPIPESTATUSPPIDPWDRANDOMREPLYSECONDSSHELLOPTSSHLVLUIDBASH_ENVCDPATHCOLUMNSCOMPREPLYEMACSFCEDITFIGNOREGLOBIGNOREHISTCONTROLHISTFILEHISTFILESIZEHISTIGNOREHISTSIZEHISTTIMEFORMATHOMEHOSTFILEIFSIGNOREEOFINPUTRCLANGLC_ALLLC_COLLATELC_CTYPELC_MESSAGESLC_NUMERICLINESMAILMAILCHECKMAILPATHOPTERRPATHPOSIXLY_CORRECTPROMPT_COMMANDPROMPT_DIRTRIMPS1PS2PS3PS4SHELLTIMEFORMATTMOUTTMPDIRauto_resumehistchars

Content preview from Pro Bash Programming: Scripting the GNU/Linux Shell

CHAPTER 9Reserved Words and Builtin Commands

There are almost 60 builtin commands and more than 20 reserved words in bash. Some of them are indispensable, and some are rarely used in scripts. Some are used primarily at the command line, and some are seldom seen anywhere. Some have been discussed already, and others will be used extensively in future chapters.

The reserved words (also called keywords) are !, case, coproc, do, done, elif, else, esac, fi, for, function, if, in, select, then, until, while, {, }, time, [[, and ]]. All except coproc, select, and time have been covered earlier in the book.

In addition to the standard commands, new builtin commands can be dynamically loaded into the shell at runtime. The bash source code package has ...