perlreref - Perl Regular Expressions Reference
This is a quick reference to Perl's regular expressions. For full information seeperlre andperlop, as well as the"SEE ALSO" section in this document.
=~ determines to which variable the regex is applied. In its absence, $_ is used.
$var =~ /foo/;!~ determines to which variable the regex is applied, and negates the result of the match; it returns false if the match succeeds, and true if it fails.
$var !~ /foo/;m/pattern/msixpogcdualn searches a string for a pattern match, applying the given options.
m Multiline mode - ^ and $ match internal liness match as a Single line - . matches \ni case-Insensitivex eXtended legibility - free whitespace and commentsp Preserve a copy of the matched string - ${^PREMATCH}, ${^MATCH}, ${^POSTMATCH} will be defined.o compile pattern Onceg Global - all occurrencesc don't reset pos on failed matches when using /ga restrict \d, \s, \w and [:posix:] to match ASCII onlyaa (two a's) also /i matches exclude ASCII/non-ASCIIl match according to current localeu match according to Unicode rulesd match according to native rules unless something indicates Unicoden Non-capture mode. Don't let () fill in $1, $2, etc...If 'pattern' is an empty string, the lastsuccessfully matched regex is used. Delimiters other than '/' may be used for both this operator and the following ones. The leadingm can be omitted if the delimiter is '/'.
qr/pattern/msixpodualn lets you store a regex in a variable, or pass one around. Modifiers as form//, and are stored within the regex.
s/pattern/replacement/msixpogcedual substitutes matches of 'pattern' with 'replacement'. Modifiers as form//, with two additions:
e Evaluate 'replacement' as an expressionr Return substitution and leave the original string untouched.'e' may be specified multiple times. 'replacement' is interpreted as a double quoted string unless a single-quote (') is the delimiter.
m?pattern? is likem/pattern/ but matches only once. No alternate delimiters can be used. Must be reset with reset().
\ Escapes the character immediately following it. Matches any single character except a newline (unless /s is used)^ Matches at the beginning of the string (or line, if /m is used)$ Matches at the end of the string (or line, if /m is used)* Matches the preceding element 0 or more times+ Matches the preceding element 1 or more times? Matches the preceding element 0 or 1 times{...} Specifies a range of occurrences for the element preceding it[...] Matches any one of the characters contained within the brackets(...) Groups subexpressions for capturing to $1, $2...(?:...) Groups subexpressions without capturing (cluster)| Matches either the subexpression preceding or following it\g1 or \g{1}, \g2 ... Matches the text from the Nth group\1, \2, \3 ... Matches the text from the Nth group\g-1 or \g{-1}, \g-2 ... Matches the text from the Nth previous group\g{name} Named backreference\k<name> Named backreference\k'name' Named backreference(?P=name) Named backreference (python syntax)These work as in normal strings.
\a Alarm (beep)\e Escape\f Formfeed\n Newline\r Carriage return\t Tab\037 Char whose ordinal is the 3 octal digits, max \777\o{2307} Char whose ordinal is the octal number, unrestricted\x7f Char whose ordinal is the 2 hex digits, max \xFF\x{263a} Char whose ordinal is the hex number, unrestricted\cx Control-x\N{name} A named Unicode character or character sequence\N{U+263D} A Unicode character by hex ordinal\l Lowercase next character\u Titlecase next character\L Lowercase until \E\U Uppercase until \E\F Foldcase until \E\Q Disable pattern metacharacters until \E\E End modificationFor Titlecase, see"Titlecase".
This one works differently from normal strings:
\b An assertion, not backspace, except in a character class[amy] Match 'a', 'm' or 'y'[f-j] Dash specifies "range"[f-j-] Dash escaped or at start or end means 'dash'[^f-j] Caret indicates "match any character _except_ these"The following sequences (except\N) work within or without a character class. The first six are locale aware, all are Unicode aware. Seeperllocale andperlunicode for details.
\d A digit\D A nondigit\w A word character\W A non-word character\s A whitespace character\S A non-whitespace character\h A horizontal whitespace\H A non horizontal whitespace\N A non newline (when not followed by '{NAME}';; not valid in a character class; equivalent to [^\n]; it's like '.' without /s modifier)\v A vertical whitespace\V A non vertical whitespace\R A generic newline (?>\v|\x0D\x0A)\pP Match P-named (Unicode) property\p{...} Match Unicode property with name longer than 1 character\PP Match non-P\P{...} Match lack of Unicode property with name longer than 1 char\X Match Unicode extended grapheme clusterPOSIX character classes and their Unicode and Perl equivalents:
ASCII- Full- POSIX range range backslash[[:...:]] \p{...} \p{...} sequence Description-----------------------------------------------------------------------alnum PosixAlnum XPosixAlnum 'alpha' plus 'digit'alpha PosixAlpha XPosixAlpha Alphabetic charactersascii ASCII Any ASCII characterblank PosixBlank XPosixBlank \h Horizontal whitespace; full-range also written as \p{HorizSpace}cntrl PosixCntrl XPosixCntrl Control charactersdigit PosixDigit XPosixDigit \d Decimal digitsgraph PosixGraph XPosixGraph 'alnum' plus 'punct'lower PosixLower XPosixLower Lowercase charactersprint PosixPrint XPosixPrint 'graph' plus 'space', but not any Controlspunct PosixPunct XPosixPunct Punctuation and Symbols in ASCII-range; just punct outside itspace PosixSpace XPosixSpace \s Whitespaceupper PosixUpper XPosixUpper Uppercase charactersword PosixWord XPosixWord \w 'alnum' + Unicode marks + connectors, like '_' (Perl extension)xdigit ASCII_Hex_Digit XPosixDigit Hexadecimal digit, ASCII-range is [0-9A-Fa-f]Also, various synonyms like\p{Alpha} for\p{XPosixAlpha}; all listed in"Properties accessible through \p{} and \P{}" in perluniprops
Within a character class:
POSIX traditional Unicode[:digit:] \d \p{Digit}[:^digit:] \D \P{Digit}All are zero-width assertions.
^ Match string start (or line, if /m is used)$ Match string end (or line, if /m is used) or before newline\b{} Match boundary of type specified within the braces\B{} Match wherever \b{} doesn't match\b Match word boundary (between \w and \W)\B Match except at word boundary (between \w and \w or \W and \W)\A Match string start (regardless of /m)\Z Match string end (before optional newline)\z Match absolute string end\G Match where previous m//g left off\K Keep the stuff left of the \K, don't include it in $&Quantifiers are greedy by default and match thelongest leftmost.
Maximal Minimal Possessive Allowed range------- ------- ---------- -------------{n,m} {n,m}? {n,m}+ Must occur at least n times but no more than m times{n,} {n,}? {n,}+ Must occur at least n times{,n} {,n}? {,n}+ Must occur at most n times{n} {n}? {n}+ Must occur exactly n times* *? *+ 0 or more times (same as {0,})+ +? ++ 1 or more times (same as {1,})? ?? ?+ 0 or 1 time (same as {0,1})The possessive forms (new in Perl 5.10) prevent backtracking: what gets matched by a pattern with a possessive quantifier will not be backtracked into, even if that causes the whole match to fail.
(?#text) A comment(?:...) Groups subexpressions without capturing (cluster)(?pimsx-imsx:...) Enable/disable option (as per m// modifiers)(?=...) Zero-width positive lookahead assertion(*pla:...) Same, starting in 5.32; experimentally in 5.28(*positive_lookahead:...) Same, same versions as *pla(?!...) Zero-width negative lookahead assertion(*nla:...) Same, starting in 5.32; experimentally in 5.28(*negative_lookahead:...) Same, same versions as *nla(?<=...) Zero-width positive lookbehind assertion(*plb:...) Same, starting in 5.32; experimentally in 5.28(*positive_lookbehind:...) Same, same versions as *plb(?<!...) Zero-width negative lookbehind assertion(*nlb:...) Same, starting in 5.32; experimentally in 5.28(*negative_lookbehind:...) Same, same versions as *plb(?>...) Grab what we can, prohibit backtracking(*atomic:...) Same, starting in 5.32; experimentally in 5.28(?|...) Branch reset(?<name>...) Named capture(?'name'...) Named capture(?P<name>...) Named capture (python syntax)(?[...]) Extended bracketed character class(?{ code }) Embedded code, return value becomes $^R(??{ code }) Dynamic regex, return value used as regex(?N) Recurse into subpattern number N(?-N), (?+N) Recurse into Nth previous/next subpattern(?R), (?0) Recurse at the beginning of the whole pattern(?&name) Recurse into a named subpattern(?P>name) Recurse into a named subpattern (python syntax)(?(cond)yes|no)(?(cond)yes) Conditional expression, where "(cond)" can be: (?=pat) lookahead; also (*pla:pat) (*positive_lookahead:pat) (?!pat) negative lookahead; also (*nla:pat) (*negative_lookahead:pat) (?<=pat) lookbehind; also (*plb:pat) (*lookbehind:pat) (?<!pat) negative lookbehind; also (*nlb:pat) (*negative_lookbehind:pat) (N) subpattern N has matched something (<name>) named subpattern has matched something ('name') named subpattern has matched something (?{code}) code condition (R) true if recursing (RN) true if recursing into Nth subpattern (R&name) true if recursing into named subpattern (DEFINE) always false, no no-pattern allowed$_ Default variable for operators to use$` Everything prior to matched string$& Entire matched string$' Everything after to matched string${^PREMATCH} Everything prior to matched string${^MATCH} Entire matched string${^POSTMATCH} Everything after to matched stringNote to those still using Perl 5.18 or earlier: The use of$`,$& or$' will slow downall regex use within your program. Consultperlvar for@- to see equivalent expressions that won't cause slow down. See alsoDevel::SawAmpersand. Starting with Perl 5.10, you can also use the equivalent variables${^PREMATCH},${^MATCH} and${^POSTMATCH}, but for them to be defined, you have to specify the/p (preserve) modifier on your regular expression. In Perl 5.20, the use of$`,$& and$' makes no speed difference.
$1, $2 ... hold the Xth captured expr$+ Last parenthesized pattern match$^N Holds the most recently closed capture$^R Holds the result of the last (?{...}) expr@- Offsets of starts of groups. $-[0] holds start of whole match@+ Offsets of ends of groups. $+[0] holds end of whole match%+ Named capture groups%- Named capture groups, as array refsCaptured groups are numbered according to theiropening paren.
lc Lowercase a stringlcfirst Lowercase first char of a stringuc Uppercase a stringucfirst Titlecase first char of a stringfc Foldcase a stringpos Return or set current match positionquotemeta Quote metacharactersreset Reset m?pattern? statusstudy Analyze string for optimizing matchingsplit Use a regex to split a string into partsThe first five of these are like the escape sequences\L,\l,\U,\u, and\F. For Titlecase, see"Titlecase"; For Foldcase, see"Foldcase".
Unicode concept which most often is equal to uppercase, but for certain characters like the German "sharp s" there is a difference.
Unicode form that is useful when comparing strings regardless of case, as certain characters have complex one-to-many case mappings. Primarily a variant of lowercase.
Iain Truskett. Updated by the Perl 5 Porters.
This document may be distributed under the same terms as Perl itself.
perlretut for a tutorial on regular expressions.
perlrequick for a rapid tutorial.
perlre for more details.
perlvar for details on the variables.
perlop for details on the operators.
perlfunc for details on the functions.
perlfaq6 for FAQs on regular expressions.
perlrebackslash for a reference on backslash sequences.
perlrecharclass for a reference on character classes.
There module to alter behaviour and aid debugging.
perluniintro,perlunicode,charnames andperllocale for details on regexes and internationalisation.
Mastering Regular Expressions by Jeffrey Friedl (https://www.oreilly.com/library/view/-/0596528124/) for a thorough grounding and reference on the topic.
David P.C. Wollmann, Richard Soderberg, Sean M. Burke, Tom Christiansen, Jim Cromie, and Jeffrey Goff for useful advice.
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The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. Please contact them via thePerl issue tracker, themailing list, orIRC to report any issues with the contents or format of the documentation.