Perl | Regex Cheat Sheet - GeeksforGeeks

Regex or Regular Expressions are an important part of Perl Programming. It is used for searching the specified text pattern. 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31Jul,2019RegexorRegularExpressionsareanimportantpartofPerlProgramming.Itisusedforsearchingthespecifiedtextpattern.Inthis,setofcharacterstogetherformthesearchpattern.Itisalsoknownasregexp.Whenuserlearnsregularexpressionthentheremightbeaneedforquicklookofthoseconceptswhichhedidn’tuseoften.Sotoprovidethatfacility,aregexcheatsheetiscreatedwhichcontainsthedifferentclasses,Characters,modifiersetc.whichareusedinregularexpression.CharacterClassesCharacterclassesareusedtomatchthestringofcharacters.Theseclasseslettheusermatchanyrangeofcharacters,whichuserdon’tknowinadvance.ClassesExplanation[abc.]Itincludesonlyoneofspecifiedcharactersi.e.‘a’,‘b’,‘c’,or‘.’[a-j]Itincludesallthecharactersfromatoj.[a-z]Itincludesalllowercasecharactersfromatoz.[^az]Itincludesallcharactersexceptaandz.\wItincludesallcharacterslike[a-z,A-Z,0-9]\dItmatchesforthedigitslike[0-9][ab][^cde]Itmatchesthatthecharactersaandbshouldnotbefollowedbyc,dande.\sItmatchesfor[\f\t\n\r]i.eformfeed,tab,newlineandcarriagereturn.\WComplementof\w\DComplementof\d\SComplementof\sExample:#Perlprogramtodemonstrate#characterclass    #ActualString$str="45char";    #Printsmatchfoundif #itsfoundin$str#byusing\wif($str=~/[\w]/){    print"MatchFound\n";}    #Printsmatchnotfound #ifitisnotfoundin$strelse{    print"MatchNotFound\n";}Output:MatchFoundAnchorsAnchorsdonotmatchanycharacteratall.Instead,theymatchaparticularpositionasbefore,after,orbetweenthecharacters.AnchorsExplanation^Itmatchesatthebeginningofthestring.$Itmatchesattheendofthestring.\bItmatchesatthewordboundaryofthestringfrom\wto\W.\AItmatchesatthebeginningofthestring.\ZItmatchesattheendingofthestringorbeforethenewline.\zItmatchesonlyattheendofthestring.\GItmatchesatthespecifiedpositionpos().\p{….}UnicodecharacterclasslikeIsLower,IsAlphaetc.\P{….}ComplementofUnicodecharacterclass[:class:]POSIXCharacterClasseslikedigit,lower,asciietc.Example:#Perlprogramtodemonstrate#useofanchorsinregex    #ActualString$str="55";    #Printsmatchfoundif #itsfoundin$str#usingAnchors/ if($str=~/[[:alpha:]]/){    print"MatchFound\n";}    #Printsmatchnotfound #ifitisnotfoundin$strelse{    print"MatchNotFound\n";}Output:MatchNotFoundMetaCharactersMetacharactersareusedtomatchpatternsinPerlregularexpressions.Allthemetacharactersmustbeescaped.CharactersExplanation^Tocheckthebeginningofthestring.$Tochecktheendingofthestring..Anycharacterexceptnewline.*Matches0ormoretimes.+Matches1ormoretimes.?Matches0ormoretimes.()Usedforgrouping.\Useforquoteorspecialcharacters.[]Usedforsetofcharacters.{}Usedasrepetitionmodifier.QuantifiersTheseareusedtocheckforthespecialcharacters.Therearethreetypesofquantifiers‘?’Itmatchesfor0or1occurrenceofcharacter.‘+’Itmatchesfor1ormoreoccurrenceofcharacter.‘*’Itmatchesfor0ormoreoccurrenceofcharacter.UsingQuantifiersExplanationa?Itchecksif‘a’occurs0or1time.a+Itchecksif‘a’occurs1ormoretimea*Itchecksif‘a’occurs0ormoretimea{2,6}Itchecksif‘a’occurs2to6timesa{2,}Itchecksif‘a’occurs2toinfinitetimesa{2}Itchecksif‘a’occurs2time.Example:#Perlprogramtodemonstrate#useofquantifiersinregex    #ActualString$str="color";    #Printsmatchfoundif #itsfoundin$str#usingquantifier?if($str=~/colou?r/){    print"MatchFound\n";}    #Printsmatchnotfound #ifitisnotfoundin$strelse{    print"MatchNotFound\n";}Output:MatchFoundModifiersModifiersExplanation\gItisusedtoreplacealltheoccurrenceofstring.\gcItallowscontinuedsearchafter\gmatchfails.\sIttreatsstringasasingleline.iItturnsoffthecasesensitivity.\xItdisregardallthewhitespaces.(?#text)Itisusedtoaddcommentinthecode.(?:pattern)Itisusedtomatchpatternofthenoncapturinggroup.(?|pattern)Itisusedtomatchpatternofthebranchtest.(?=pattern)Itisusedforpositivelookaheadassertion.(?!pattern)Itisusedfornegativelookaheadassertion.(<=pattern)Itisusedforpositivelookbehindassertion.(