外文翻译--高级Bash脚本编程指南一个对脚本编程技术的深入讨论.doc

附录外文资料翻译原文部分AdvancedBash-ScriptingGuideAnin-depthexplorationoftheartofshellscripting1.IntroductionTheshellisacommandinterpreter.Morethanjusttheinsulatinglayerbetweentheoperatingsystemkernelandtheuser,itsalsoafairlypowerfulprogramminglanguage.Ashellprogram,calledascript,isaneasy-to-usetoolforbuildingapplicationsbygluingtogethersystemcalls,tools,utilities,andcompiledbinaries.VirtuallytheentirerepertoireofUNIXcommands,utilities,andtoolsisavailableforinvocationbyashellscript.Ifthatwerenotenough,internalshellcommands,suchastestingandloopconstructs,giveadditionalpowerandflexibilitytoscripts.Shellscriptslendthemselvesexceptionallywelltoadministrativesystemtasksandotherroutinerepetitivejobsnotrequiringthebellsandwhistlesofafull-blowntightlystructuredprogramminglanguage.2.WhyShellProgramming?Aworkingknowledgeofshellscriptingisessentialtoanyonewishingtobecomereasonablyproficientatsystemadministration,eveniftheydonotanticipateeverhavingtoactuallywriteascript.ConsiderthatasaLinuxmachinebootsup,itexecutestheshellscriptsin/etc/rc.dtorestorethesystemconfigurationandsetupservices.Adetailedunderstandingofthesestartupscriptsisimportantforanalyzingthebehaviorofasystem,andpossiblymodifyingit.Writingshellscriptsisnothardtolearn,sincethescriptscanbebuiltinbite-sizedsectionsandthereisonlyafairlysmallsetofshell-specificoperatorsandoptionstolearn.Thesyntaxissimpleandstraightforward,similartothatofinvokingandchainingtogetherutilitiesatthecommandline,andthereareonlyafewrulestolearn.Mostshortscriptsworkrightthefirsttime,anddebuggingeventhelongeronesisstraightforward.Ashellscriptisaquickanddirtymethodofprototypingacomplexapplication.Gettingevenalimitedsubsetofthefunctionalitytoworkinashellscriptisoftenausefulfirststageinprojectdevelopment.Thisway,thestructureoftheapplicationcanbetestedandplayedwith,andthemajorpitfallsfoundbeforeproceedingtothefinalcodinginC,C+,Java,orPerl.ShellscriptinghearkensbacktotheclassicUNIXphilosophyofbreakingcomplexprojectsintosimplersubtasks,ofchainingtogethercomponentsandutilities.Manyconsiderthisabetter,oratleastmoreestheticallypleasingapproachtoproblemsolvingthanusingoneofthenewgenerationofhighpoweredall-in-onelanguages,suchasPerl,whichattempttobeallthingstoallpeople,butatthecostofforcingyoutoalteryourthinkingprocessestofitthetool.WhennottouseshellscriptsResource-intensivetasks,especiallywherespeedisafactor(sorting,hashing,etc.)Proceduresinvolvingheavy-dutymathoperations,especiallyfloatingpointarithmetic,arbitraryprecisioncalculations,orcomplexnumbers(useC+orFORTRANinstead)Cross-platformportabilityrequired(useCorJavainstead)Complexapplications,wherestructuredprogrammingisanecessity(needtype-checkingofvariables,functionprototypes,etc.)Mission-criticalapplicationsuponwhichyouarebettingtheranch,orthefutureofthecompanySituationswheresecurityisimportant,whereyouneedtoguaranteetheintegrityofyoursystemandprotectagainstintrusion,cracking,andvandalismProjectconsistsofsubcomponentswithinterlockingdependenciesExtensivefileoperationsrequired(Bashislimitedtoserialfileaccess,andthatonlyinaparticularlyclumsyandinefficientline-by-linefashion)Neednativesupportformulti-dimensionalarraysNeeddatastructures,suchaslinkedlistsortreesNeedtogenerateormanipulategraphicsorGUIsNeeddirectaccesstosystemhardwareNeedportorsocketI/ONeedtouselibrariesorinterfacewithlegacycodeProprietary,closed-sourceapplications(shellscriptsputthesourcecoderightoutintheopenforalltheworldtosee)Ifanyoftheaboveapplies,consideramorepowerfulscriptinglanguage-perhapsPerl,Tcl,Python,Ruby-orpossiblyahigh-levelcompiledlanguagesuchasC,C+,orJava.Eventhen,prototypingtheapplicationasashellscriptmightstillbeausefuldevelopmentstep.WewillbeusingBash,anacronymforBourne-AgainshellandapunonStephenBournesnowclassicBourneshell.BashhasbecomeadefactostandardforshellscriptingonallflavorsofUNIX.Mostoftheprinciplesthisbookcoversapplyequallywelltoscriptingwithothershells,suchastheKornShell,fromwhichBashderivessomeofitsfeatures,andtheCShellanditsvariants.(NotethatCShellprogrammingisnotrecommendedduetocertaininherentproblems,aspointedoutinanOctober,1993UsenetpostbyTomChristiansen.)Whatfollowsisatutorialonshellscripting.Itreliesheavilyonexamplestoillustratevariousfeaturesoftheshell.Theexamplescriptswork-theyvebeentested,insofaraswaspossible-andsomeofthemareevenusefulinreallife.Thereadercanplaywiththeactualworkingcodeoftheexamplesinthesourcearchive(scriptname.shorscriptname.bash),givethemexecutepermission(chmodu+rxscriptname),thenrunthemtoseewhathappens.Shouldthesourcearchivenotbeavailable,thencut-and-pastefromtheHTML,pdf,ortextrenderedversions.Beawarethatsomeofthescriptspresentedhereintroducefeaturesbeforetheyareexplained,andthismayrequirethereadertotemporarilyskipaheadforenlightenment.外文资料翻译译文部分高级Bash脚本编程指南一个对脚本编程技术的深入讨论1：简介Shell是一个命令解释器。它是操作系统内核和用户之间的绝缘层，也是一种功能强大的编程语言。一个Shell程序，通常被称作为脚本，它是由系统调用，命令工具，软件包和已编译的二进制包结合起来的容易使用的工具。事实上，shell脚本可以调用整个UNIX系统命令，软件包和工具。如果这还不太够的话，Shell的内部命令，如测试和循环结构，都使得Shell脚本更强大和更有弹性。Shell脚本在管理系统任务中表现得非常出色，在对日常反复性的处理工作中避免使用那些结构复杂的程序语言。2：为什么要用Shell编程?脚本应用知识对希望精通系统管理的任何个人说是必需的，他实际上不想写一个脚本程序。一般说一个Linux机器启动后，它会执行在/etc/rc.d目录下的Shell脚本重建系统环境并且启动各种服务。理解这些启动脚本的细节对分析系统运作并修改它是有很大意义的。编写shell脚本并不难学，因为脚本内建的功能集（check?）和他们只要学相当少的shell的操作符和选项。语法简单易懂，像在命令行上调用和连接软件包那样容易，它只有少量的规则需要掌握。大多数短小的脚本第一次就工作的很好，较长的脚本