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Perl编程,与UNIX无关.pdf

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ThePERLProgrammingLanguage LarryWall <lwall@netlabs.com> ABSTRACT ThePracticalExtractionandReportLanguage(perl)isaninterpretedlanguage optimizedforscanningarbitrarytextfiles,extractinginformationfromthosetextfiles, andprintingreportsbasedonthatinformation.Itisalsoagoodlanguageformanysys- temmanagementtasks.Thelanguageisintendedtobepractical(easytouse,efficient, complete)ratherthanbeautiful(tiny,elegant,minimal).Itcombines(intheauthor’s opinion,anyway)someofthebestfeaturesofC,sed,awk,andsh,sopeoplefamiliarwith thoselanguagesshouldhavelittledifficultywithit.(Languagehistorianswillalsonote somevestigesofcsh,Pascal,andevenBASIC-PLUS.)Expressionsyntaxcorresponds quitecloselytoCexpressionsyntax.UnlikemostUnixutilities,perldoesnotarbitrarily limitthesizeofyourdata—ifyou’vegotthememory,perlcanslurpinyourwholefile asasinglestring.Recursionisofunlimiteddepth.Andthehashtablesusedbyassocia- tivearraysgrowasnecessarytopreventdegradedperformance.Perlusessophisticated patternmatchingtechniquestoscanlargeamountsofdataveryquickly.Althoughopti- mizedforscanningtext,perlcanalsodealwithbinarydata,andcanmakedbmfileslook likeassociativearrays(wheredbmisavailable).SetuidperlscriptsaresaferthanCpro- gramsthroughadataflowtracingmechanismwhichpreventsmanystupidsecurityholes. Ifyouhaveaproblemthatwouldordinarilyusesedorawkorsh,butitexceedstheir capabilitiesormustrunalittlefaster,andyoudon’twanttowritethesillythinginC, thenperlmaybeforyou.Therearealsotranslatorstoturnyoursedandawkscripts intoperlscripts. 1.DataTypesandObjects Perlhasthreedatatypes:scalars,arraysofscalars,andassociativearraysofscalars.Normalarrays areindexedbynumber,andassociativearraysbystring. Theinterpretationofoperationsandvaluesinperlsometimesdependsontherequirementsofthe contextaroundtheoperationorvalue.Therearethreemajorcontexts:string,numericandarray.Certain operationsreturnarrayvaluesincontextswantinganarray,andscalarvaluesotherwise.(Ifthisistrueof anoperationitwillbementionedinthedocumentationforthatoperation.)Operations