pcresyntax(3) - Linux man page
Name
PCRE - Perl-compatible regular expressions
Pcre Regular Expression Syntax Summary
The full syntax and semantics of the regular expressions that are supported by PCRE are described in the pcrepattern documentation. This document contains just a quick-reference summary of the syntax.
Quoting
\x where x is non-alphanumeric is a literal x \Q...\E treat enclosed characters as literal
Characters
\a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is any character \e escape (hex 1B) \f form feed (hex 0C) \n newline (hex 0A) \r carriage return (hex 0D) \t tab (hex 09) \ddd character with octal code ddd, or backreference \xhh character with hex code hh \x{hhh..} character with hex code hhh..
Character Types
. any character except newline; in dotall mode, any character whatsoever \C one byte, even in UTF-8 mode (best avoided) \d a decimal digit \D a character that is not a decimal digit \h a horizontal white space character \H a character that is not a horizontal white space character \p{xx} a character with the xx property \P{xx} a character without the xx property \R a newline sequence \s a white space character \S a character that is not a white space character \v a vertical white space character \V a character that is not a vertical white space character \w a "word" character \W a "non-word" character \X an extended Unicode sequence
In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.
GENERAL CATEGORY PROPERTY CODES FOR \p and \P
C Other Cc Control Cf Format Cn Unassigned Co Private use Cs Surrogate
L Letter Ll Lower case letter Lm Modifier letter Lo Other letter Lt Title case letter Lu Upper case letter L& Ll, Lu, or Lt
M Mark Mc Spacing mark Me Enclosing mark Mn Non-spacing mark
N Number Nd Decimal number Nl Letter number No Other number
P Punctuation Pc Connector punctuation Pd Dash punctuation Pe Close punctuation Pf Final punctuation Pi Initial punctuation Po Other punctuation Ps Open punctuation
S Symbol Sc Currency symbol Sk Modifier symbol Sm Mathematical symbol So Other symbol
Z Separator Zl Line separator Zp Paragraph separator Zs Space separator
SCRIPT NAMES FOR \p AND \P
Arabic, Armenian, Balinese, Bengali, Bopomofo, Braille, Buginese, Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin, Limbu, Linear_B, Malayalam, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician, Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
Character Classes
[...] positive character class [^...] negative character class [x-y] range (can be used for hex characters) [[:xxx:]] positive POSIX named set [[:^xxx:]] negative POSIX named set
alnum alphanumeric alpha alphabetic ascii 0-127 blank space or tab cntrl control character digit decimal digit graph printing, excluding space lower lower case letter print printing, including space punct printing, excluding alphanumeric space white space upper upper case letter word same as \w xdigit hexadecimal digit
In PCRE, POSIX character set names recognize only ASCII characters. You can use \Q...\E inside a character class.
Quantifiers
? 0 or 1, greedy ?+ 0 or 1, possessive ?? 0 or 1, lazy * 0 or more, greedy *+ 0 or more, possessive *? 0 or more, lazy + 1 or more, greedy ++ 1 or more, possessive +? 1 or more, lazy {n} exactly n {n,m} at least n, no more than m, greedy {n,m}+ at least n, no more than m, possessive {n,m}? at least n, no more than m, lazy {n,} n or more, greedy {n,}+ n or more, possessive {n,}? n or more, lazy
Anchors And Simple Assertions
\b word boundary \B not a word boundary ^ start of subject also after internal newline in multiline mode \A start of subject $ end of subject also before newline at end of subject also before internal newline in multiline mode \Z end of subject also before newline at end of subject \z end of subject \G first matching position in subject
Match Point Reset
\K reset start of match
Alternation
expr|expr|expr...
Capturing
(...) capturing group (?<name>...) named capturing group (Perl) (?'name'...) named capturing group (Perl) (?P<name>...) named capturing group (Python) (?:...) non-capturing group (?|...) non-capturing group; reset group numbers for capturing groups in each alternative
Atomic Groups
(?>...) atomic, non-capturing group
Comment
(?#....) comment (not nestable)
Option Setting
(?i) caseless (?J) allow duplicate names (?m) multiline (?s) single line (dotall) (?U) default ungreedy (lazy) (?x) extended (ignore white space) (?-...) unset option(s)
Lookahead And Lookbehind Assertions
(?=...) positive look ahead (?!...) negative look ahead (?<=...) positive look behind (?<!...) negative look behind
Each top-level branch of a look behind must be of a fixed length.
Backreferences
\n reference by number (can be ambiguous) \gn reference by number \g{n} reference by number \g{-n} relative reference by number \k<name> reference by name (Perl) \k'name' reference by name (Perl) \g{name} reference by name (Perl) \k{name} reference by name (.NET) (?P=name) reference by name (Python)
SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
(?R) recurse whole pattern (?n) call subpattern by absolute number (?+n) call subpattern by relative number (?-n) call subpattern by relative number (?&name) call subpattern by name (Perl) (?P>name) call subpattern by name (Python) \g<name> call subpattern by name (Oniguruma) \g'name' call subpattern by name (Oniguruma) \g<n> call subpattern by absolute number (Oniguruma) \g'n' call subpattern by absolute number (Oniguruma) \g<+n> call subpattern by relative number (PCRE extension) \g'+n' call subpattern by relative number (PCRE extension) \g<-n> call subpattern by relative number (PCRE extension) \g'-n' call subpattern by relative number (PCRE extension)
Conditional Patterns
(?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern)
(?(n)... absolute reference condition (?(+n)... relative reference condition (?(-n)... relative reference condition (?(<name>)... named reference condition (Perl) (?('name')... named reference condition (Perl) (?(name)... named reference condition (PCRE) (?(R)... overall recursion condition (?(Rn)... specific group recursion condition (?(R&name)... specific recursion condition (?(DEFINE)... define subpattern for reference (?(assert)... assertion condition
Backtracking Control
The following act immediately they are reached:
(*ACCEPT) force successful match (*FAIL) force backtrack; synonym (*F)
The following act only when a subsequent match failure causes a backtrack to reach them. They all force a match failure, but they differ in what happens afterwards. Those that advance the start-of-match point do so only if the pattern is not anchored.
(*COMMIT) overall failure, no advance of starting point (*PRUNE) advance to next starting character (*SKIP) advance start to current matching position (*THEN) local failure, backtrack to next alternation
Newline Conventions
These are recognized only at the very start of the pattern or after a (*BSR_...) option.
(*CR) (*LF) (*CRLF) (*ANYCRLF) (*ANY)
WHAT \R MATCHES
These are recognized only at the very start of the pattern or after a (*...) option that sets the newline convention.
(*BSR_ANYCRLF) (*BSR_UNICODE)
Callouts
(?C) callout (?Cn) callout with data n
See Also
pcrepattern(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).
Author
Philip Hazel University Computing Service Cambridge CB2 3QH, England.
Revision
Last updated: 09 April 2008 Copyright © 1997-2008 University of Cambridge.