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 (c) 1997-2008 University of Cambridge.