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ThePERLProgrammingLanguageLarryWall<lwall@netlabs.com>ABSTRACTThePracticalExtractionandReportLanguage(perl)isaninterpretedlanguageoptimizedforscanningarbitrarytextfiles,extractinginformationfromthosetextfiles,andprintingreportsbasedonthatinformation.Itisalsoagoodlanguageformanysys-temmanagementtasks.Thelanguageisintendedtobepractical(easytouse,efficient,complete)ratherthanbeautiful(tiny,elegant,minimal).Itcombines(intheauthor’sopinion,anyway)someofthebestfeaturesofC,sed,awk,andsh,sopeoplefamiliarwiththoselanguagesshouldhavelittledifficultywithit.(Languagehistorianswillalsonotesomevestigesofcsh,Pascal,andevenBASIC-PLUS.)ExpressionsyntaxcorrespondsquitecloselytoCexpressionsyntax.UnlikemostUnixutilities,perldoesnotarbitrarilylimitthesizeofyourdata—ifyou’vegotthememory,perlcanslurpinyourwholefileasasinglestring.Recursionisofunlimiteddepth.Andthehashtablesusedbyassocia-tivearraysgrowasnecessarytopreventdegradedperformance.Perlusessophisticatedpatternmatchingtechniquestoscanlargeamountsofdataveryquickly.Althoughopti-mizedforscanningtext,perlcanalsodealwithbinarydata,andcanmakedbmfileslooklikeassociativearrays(wheredbmisavailable).SetuidperlscriptsaresaferthanCpro-gramsthroughadataflowtracingmechanismwhichpreventsmanystupidsecurityholes.Ifyouhaveaproblemthatwouldordinarilyusesedorawkorsh,butitexceedstheircapabilitiesormustrunalittlefaster,andyoudon’twanttowritethesillythinginC,thenperlmaybeforyou.Therearealsotranslatorstoturnyoursedandawkscriptsintoperlscripts.1.DataTypesandObjectsPerlhasthreedatatypes:scalars,arraysofscalars,andassociativearraysofscalars.Normalarraysareindexedbynumber,andassociativearraysbystring.Theinterpretationofoperationsandvaluesinperlsometimesdependsontherequirementsofthecontextaroundtheoperationorvalue.Therearethreemajorcontexts:string,numericandarray.Certainoperationsreturnarrayvaluesincontextswantinganarray,andscalarvaluesotherwise.(Ifthisistrueofanoperationitwillbementionedinthedocumentationforthatoperation.)Operations