Programmatically read from STDIN or input file in Perl

while (<>) { print; }. will read either from a file specified on the command line or from stdin if no file is given. If you are required this loop ... Home Public Questions Tags Users Companies Collectives ExploreCollectives Teams StackOverflowforTeams –Startcollaboratingandsharingorganizationalknowledge. CreateafreeTeam WhyTeams? Teams CreatefreeTeam StackOverflowforTeamsismovingtoitsowndomain!Whenthemigrationiscomplete,youwillaccessyourTeamsatstackoverflowteams.com,andtheywillnolongerappearintheleftsidebaronstackoverflow.com. Checkyouremailforupdates. Collectives™onStackOverflow Findcentralized,trustedcontentandcollaboratearoundthetechnologiesyouusemost. LearnmoreaboutCollectives Teams Q&Aforwork Connectandshareknowledgewithinasinglelocationthatisstructuredandeasytosearch. LearnmoreaboutTeams ProgrammaticallyreadfromSTDINorinputfileinPerl AskQuestion Asked 12years,3monthsago Modified 2monthsago Viewed 160ktimes 80 New!Savequestionsoranswersandorganizeyourfavoritecontent.Learnmore. Whatistheslickestwaytoprogramaticallyreadfromstdinoraninputfile(ifprovided)inPerl? perlstdin Share Improvethisquestion Follow askedJun29,2010at7:23 sykersyker 10.6k1616goldbadges5454silverbadges6868bronzebadges Addacomment  |  8Answers 8 Sortedby: Resettodefault Highestscore(default) Trending(recentvotescountmore) Datemodified(newestfirst) Datecreated(oldestfirst) 98 while(<>){ print; } willreadeitherfromafilespecifiedonthecommandlineorfromstdinifnofileisgiven Ifyouarerequiredthisloopconstructionincommandline,thenyoumayuse-noption: $perl-ne'print;' Hereyoujustputcodebetween{}fromfirstexampleinto''insecond Share Improvethisanswer Follow editedJul8,2017at13:11 EugenKonkov 19.7k1212goldbadges9494silverbadges138138bronzebadges answeredJun29,2010at7:28 ennuikillerennuikiller 45.6k1414goldbadges110110silverbadges137137bronzebadges 5 24 +1+nitpick:"willreadfromoneormorefilesconsecutivelyspecifiedonthecommandline" – msw Jun29,2010at7:57 5 ...andallyouneedtodoiswrite@ARGV="/path/to/some/file.ext";anditreadsthefile--soyoucanevenprogramadefaultfileoncertainconditions. – Axeman Jun29,2010at13:54 3 Andifyourscriptisveryshort,youcanusethe-nor-poptionstoperl,andspecifyyourprocessingonthecommandline:perl-n-e'$_=uc($_);print;'yourfile.With-pinsteadof-n,perlautomaticallyprints$_attheend. – mivk Jan9,2012at10:46 3 Andofcourseyoucan"slurp"everythinginonego:my@slurp=<>;foreachmy$line(@slurp){...} – DavidTonhofer Dec19,2013at13:45 Isthereareasonyoudon'tnamethereadlinewithsomethinglikewhile(my$line=<>){...? – DavidMertens Jan20,2018at23:16 Addacomment  |  50 Thisprovidesanamedvariabletoworkwith: foreachmy$line(){ chomp($line); print"$line\n"; } Toreadafile,pipeitinlikethis: program.pl).Thennoredirectionisnecessary. – DavidMertens Jul7,2014at16:12 3 Thefirstlineshouldreadforeachmy$line(){[email protected]'snotPerl'sfaultifPerlscriptsareunreadable.Programmersaretoblamehere! – tiktak Dec13,2014at13:01 3 Rereadingthequestionthisresponseisincorrectbecauseitonlyreadsfromstdinanddoesn'treadafilespecifiedonthecommandline.ennuikiller'sansweriscorrectalthoughIwouldwriteitaswhile(my$line=<>){print$line;}. – MikeKulls Dec14,2014at23:35 3 @MikeKullsShouldn'tthatbewhile(my$line=<>,defined$line){...}orwhile(<>){my$line=$_;}toavoidstoppingonablankline? – GregNisbet Dec14,2016at21:14  |  Show2morecomments 17 The"slickest"wayincertainsituationsistotakeadvantageofthe-nswitch.Itimplicitlywrapsyourcodewithawhile(<>)loopandhandlestheinputflexibly. InslickestWay.pl: #!/usr/bin/perl-n BEGIN:{ #dosomethingoncehere } #implementlogicforasinglelineofinput print$result; Atthecommandline: chmod+xslickestWay.pl Now,dependingonyourinputdooneofthefollowing: Waitforuserinput ./slickestWay.pl Readfromfile(s)namedinarguments(noredirectionrequired) ./slickestWay.plinput.txt ./slickestWay.plinput.txtmoreInput.txt Useapipe someOtherScript|./slickestWay.pl TheBEGINblockisnecessaryifyouneedtoinitializesomekindofobject-orientedinterface,suchasText::CSVorsomesuch,whichyoucanaddtotheshebangwith-M. -land-parealsoyourfriends. Share Improvethisanswer Follow answeredFeb10,2014at17:25 NeilBestNeilBest 79988silverbadges1616bronzebadges Addacomment  |  15 Youneedtouse<>operator: while(<>){ print$_;#orsimply"print;" } Whichcanbecompactedto: printwhile(<>); Arbitraryfile: openmy$F,"){ print$_; } close$F; Share Improvethisanswer Follow editedAug22at13:41 MUYBelgium 2,20244goldbadges3030silverbadges4343bronzebadges answeredJun29,2010at7:25 el.pescado-нетвойнеel.pescado-нетвойне 18.5k44goldbadges4545silverbadges8686bronzebadges Addacomment  |  10 Ifthereisareasonyoucan'tusethesimplesolutionprovidedbyennuikillerabove,thenyouwillhavetouseTypeglobstomanipulatefilehandles.Thisiswaymorework.Thisexamplecopiesfromthefilein$ARGV[0]tothatin$ARGV[1].ItdefaultstoSTDINandSTDOUTrespectivelyiffilesarenotspecified. useEnglish; my$in; my$out; if($#ARGV>=0){ unless(open($in,"=1){ unless(open($out,">",$ARGV[1])){ die"couldnotopen$ARGV[1]forwriting."; } } else{ $out=*STDOUT; } while($_=){ $out->print($_); } Share Improvethisanswer Follow answeredDec7,2014at18:52 Sigusr2Sigusr2 10911silverbadge22bronzebadges 2 1 +1forawaythatwillworkiffilenametoreadfromisnotprovidedoncommandlinebutsomewhereelse(insomevariable,readfromconfigfileetc-youjustreplace$ARGV[0]etcwithothervariable)whereallotheranswersfail... – MatijaNalis Oct30,2016at16:29 Or,forreading,justunshiftthefilenameonto@ARGVandusethediamondoperator,<>. – DavidMertens Jan20,2018at23:04 Addacomment  |  6 Do $userinput=;#readstdinandputitin$userinput chomp($userinput);#cutthereturn/linefeedcharacter ifyouwanttoreadjustoneline Share Improvethisanswer Follow answeredJan24,2013at13:59 ThorstenNiehuesThorstenNiehues 13.2k2020goldbadges7575silverbadges108108bronzebadges 1 OnlyreadsfromSTDIN,notfromspecifiedfile.ThediamondoperatorisexactlywhattheOPislookingfor. – DavidMertens Jan20,2018at23:14 Addacomment  |  -1 HereishowImadeascriptthatcouldtakeeithercommandlineinputsorhaveatextfileredirected. if($#ARGV<1){ @ARGV=(); @ARGV=<>; chomp(@ARGV); } Thiswillreassignthecontentsofthefileto@ARGV,fromthereyoujustprocess@ARGVasifsomeonewasincludingcommandlineoptions. WARNING Ifnofileisredirected,theprogramwillsittheiridlebecauseitiswaitingforinputfromSTDIN. IhavenotfiguredoutawaytodetectifafileisbeingredirectedinyettoeliminatetheSTDINissue. Share Improvethisanswer Follow answeredSep20,2015at18:01 WestrockWestrock 16944silverbadges1414bronzebadges 1 Thisisacoolapproach,butnotwhattheOPwasaskingfor.Thismakesitpossibletopassasinglefilenameasanargument,thecontentsofwhichareusedascommand-linearguments.OPwaslookingforsomethingdifferent.Also,whythecryptic$#ARGV<1insteadof(whatIthinkofas)moreclear@ARGV==1? – DavidMertens Jan20,2018at23:12 Addacomment  |  -3 if(my$file=shift){#iffileisspecified,readfromthat open(my$fh,'){ print$line; } } else{#otherwise,readfromSTDIN printwhile(<>); } Share Improvethisanswer Follow answeredJun29,2010at7:44 trapd00rtrapd00r 722bronzebadges 2 8 Theplain<>operatorwillautomaticallyfindandreadfromanyfile(s)givenonthecommandline.There'snoneedfortheif. – DaveSherohman Jun29,2010at8:27 Youalsodonotdescribewhatshiftisdoinghere – EugenKonkov Jul8,2017at13:14 Addacomment  |  YourAnswer ThanksforcontributingananswertoStackOverflow!Pleasebesuretoanswerthequestion.Providedetailsandshareyourresearch!Butavoid…Askingforhelp,clarification,orrespondingtootheranswers.Makingstatementsbasedonopinion;backthemupwithreferencesorpersonalexperience.Tolearnmore,seeourtipsonwritinggreatanswers. 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