Using 'Shift' in subroutine argument - PerlMonks

Dear monks, I am going through a Perl script where I found. mysub shift, shift;. [download]. where mysub is subroutine name. Clearquestionsandrunnablecodegetthebestandfastestanswer   PerlMonks   Using'Shift'insubroutineargument byAnonymousMonk Log inCreate a new user The Monastery Gates Seekers of Perl Wisdom Meditations Cool Uses For Perl Obfuscation Tutorials Poetry Reviews Perl News Donate Recent Threads Newest Nodes Super Search PerlMonks Discussion What's New onNov02,2007at10:29 UTC (#648616=perlquestion:printw/replies,xml) NeedHelp?? AnonymousMonkhasaskedforthewisdomofthePerlMonksconcerningthefollowingquestion: Dearmonks, IamgoingthroughaPerlscriptwhere Ifound mysubshift,shift; [download] wheremysubissubroutinename. Pleaseexplainwhathowargumentsarebeingpassed throughshiftitself.AsfarasIknowshiftisusedto gettheveryfirstelementofanarray.ButhereIcantsee anyarray.Arethese'shift's'takingvaluefromcommandlines?? Plhelp.CommentonUsing'Shift'insubroutineargumentDownloadCode Repliesarelisted'BestFirst'. Re:Using'Shift'insubroutineargument bymerlyn(Sage)onNov02,2007at10:49 UTC perldoc-fshifttellsus: shiftARRAY shiftShiftsthefirstvalueofthearrayoffandreturnsit, shorteningthearrayby1andmovingeverythingdown.Ift +here arenoelementsinthearray,returnstheundefinedvalue. +If ARRAYisomitted,shiftsthe@_arraywithinthelexicals +cope ofsubroutinesandformats,andthe@ARGVarrayatfilesc +opes orwithinthelexicalscopesestablishedbythe"eval''", "BEGIN{}","INIT{}","CHECK{}",and"END{}"constructs +. [download] Inthiscase,it'slikelythatit'sbeingusedwithinanothersubroutine,soit'sshiftingthe@_array. --RandalL.Schwartz,Perlhacker [reply][d/l] Re^2:Using'Shift'insubroutineargument bynarainhere(Monk)onNov02,2007at11:31 UTC Ifyouexecutethis usestrict; usewarnings; one(1,2,3,4); subone{ &two(shift,shift); } subtwo { print"Elements:\n@_\n"; } [download] youwouldget Elements: 12 [download] Whichmeansthatit'ssameaspassingthefirsttwoelementsofthelistthesub-routineonehasreceived.ThoughIwasnotabletocompilethecode subone{ &twoshift,shift; } [download] whichisyourcase.Providethesomecontextofyoursnippetthatwouldhelpeveryonetolearn. Theworldissobigforanyindividualtoconquer [reply][d/l][select] Re^3:Using'Shift'insubroutineargument byshmem(Chancellor)onNov02,2007at13:20 UTC ThoughIwasnotabletocompilethecode subone{ &twoshift,shift; } [download] That'sasyntaxerror.Subroutineinvocationswith&requireparens. Droptheampersandandmovethesubtwodefinitionup: usestrict; usewarnings; one(1,2,3,4); subtwo{ print"Elements:\n@_\n"; } subone{ twoshift,shift; } [download] Toresolvethebarewordtwoasasubroutinecall(intwoshift,shift),thecompilerneedstohaveseenthesubdeclarationalready.Alternative: usestrict; usewarnings; subtwo;#forwarddeclaration one(1,2,3,4); subone{ twoshift,shift; } subtwo{ print"Elements:\n@_\n"; } [download] --shmem _($_=""x(1<<5)."?\n".q·/)Oo.G°\/ /\_¯/(q/ ----------------------------\__(m.====·.(_("alwaysoffthecrowd"))."· ");sub_{s./.($e="'Itrs`mnsgdqGdbjO`qkdq")=~y/"-y/#-z/;$e.e&&print} [reply][d/l][select] Re:Using'Shift'insubroutineargument bysen(Hermit)onNov02,2007at10:54 UTC Hi, Asubroutine'sargumentscomeinviathespecial@_array.Theshiftwithoutanargumentdefaultsto@_. forexample, subemp{ $name=shift; $id=shift; print"name,$name,id$id"; } &emp('abc',10); [reply] Re^2:Using'Shift'insubroutineargument byGrandFather(Saint)onNov02,2007at18:43 UTC Theshiftwithoutanargumentdefaultsto@_. exceptinmainscope(outsideasub)[email protected]: perl-e"printshift"wibble [download] Prints: wibble [download] Perlisenvironmentallyfriendly-itsavestrees [reply][d/l][select] Re:Using'Shift'insubroutineargument byFunkyMonk(Chancellor)onNov03,2007at01:38 UTC I'vealwaysbelieveditwasano-notochangeavariable(@_or@ARGVinthiscase)morethanonceinasinglestatement.AsfarasIknow,Perl[1]doesn'tdefinewhichshiftwillbedonefirst. 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