pcresyntax(3)
PCRESYNTAX(3) C LIBRARY FUNCTIONS PCRESYNTAX(3)
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 a quick-reference sum-
mary 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 ASCII character
\e escape (hex 1B)
\f form feed (hex 0C)
\n newline (hex 0A)
\r carriage return (hex 0D)
\t tab (hex 09)
\0dd character with octal code 0dd
\ddd character with octal code ddd, or backreference
\o{ddd..} character with octal code ddd..
\xhh character with hex code hh
\x{hhh..} character with hex code hhh..
Note that \0dd is always an octal code, and that \8 and \9
are the literal characters "8" and "9".
CHARACTER TYPES
. any character except newline;
in dotall mode, any character whatsoever
\C one data unit, even in UTF 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
\N a character that is not a newline
\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
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\w a "word" character
\W a "non-word" character
\X a Unicode extended grapheme cluster
By default, \d, \s, and \w match only ASCII characters, even
in UTF-8 mode or in the 16- bit and 32-bit libraries. How-
ever, if locale-specific matching is happening, \s and \w
may also match characters with code points in the range
128-255. If the PCRE_UCP option is set, the behaviour of
these escape sequences is changed to use Unicode properties
and they match many more characters.
GENERAL CATEGORY PROPERTIES 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
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So Other symbol
Z Separator
Zl Line separator
Zp Paragraph separator
Zs Space separator
PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P
Xan Alphanumeric: union of properties L and N
Xps POSIX space: property Z or tab, NL, VT, FF, CR
Xsp Perl space: property Z or tab, NL, VT, FF, CR
Xuc Univerally-named character: one that can be
represented by a Universal Character Name
Xwd Perl word: property Xan or underscore
Perl and POSIX space are now the same. Perl added VT to its
space character set at release 5.18 and PCRE changed at
release 8.34.
SCRIPT NAMES FOR \p AND \P
Arabic, Armenian, Avestan, Balinese, Bamum, Bassa_Vah,
Batak, Bengali, Bopomofo, Brahmi, Braille, Buginese, Buhid,
Canadian_Aboriginal, Carian, Caucasian_Albanian, Chakma,
Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyril-
lic, Deseret, Devanagari, Duployan, Egyptian_Hieroglyphs,
Elbasan, Ethiopic, Georgian, Glagolitic, Gothic, Grantha,
Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew,
Hiragana, Imperial_Aramaic, Inherited,
Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese,
Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer,
Khojki, Khudawadi, Lao, Latin, Lepcha, Limbu, Linear_A,
Linear_B, Lisu, Lycian, Lydian, Mahajani, Malayalam, Man-
daic, Manichaean, Meetei_Mayek, Mende_Kikakui,
Meroitic_Cursive, Meroitic_Hieroglyphs, Miao, Modi, Mongo-
lian, Mro, Myanmar, Nabataean, New_Tai_Lue, Nko, Ogham,
Ol_Chiki, Old_Italic, Old_North_Arabian, Old_Permic,
Old_Persian, Old_South_Arabian, Old_Turkic, Oriya, Osmanya,
Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa, Phoenician,
Psalter_Pahlavi, Rejang, Runic, Samaritan, Saurashtra,
Sharada, Shavian, Siddham, Sinhala, Sora_Sompeng, Sundanese,
Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham,
Tai_Viet, Takri, Tamil, Telugu, Thaana, Thai, Tibetan, Tifi-
nagh, Tirhuta, Ugaritic, Vai, Warang_Citi, Yi.
CHARACTER CLASSES
[...] positive character class
[^...] negative character class
[x-y] range (can be used for hex characters)
[[:xxx:]] positive POSIX named set
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[[:^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 by default, but some of them use Unicode proper-
ties if PCRE_UCP is set. You can use \Q...\E inside a char-
acter 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
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\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
\K is honoured in positive assertions, but ignored in nega-
tive ones.
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)
The following are recognized only at the very start of a
pattern or after one of the newline or \R options with simi-
lar syntax. More than one of them may appear.
(*LIMIT_MATCH=d) set the match limit to d (decimal number)
(*LIMIT_RECURSION=d) set the recursion limit to d (decimal
number)
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(*NO_AUTO_POSSESS) no auto-possessification
(PCRE_NO_AUTO_POSSESS)
(*NO_START_OPT) no start-match optimization
(PCRE_NO_START_OPTIMIZE)
(*UTF8) set UTF-8 mode: 8-bit library (PCRE_UTF8)
(*UTF16) set UTF-16 mode: 16-bit library
(PCRE_UTF16)
(*UTF32) set UTF-32 mode: 32-bit library
(PCRE_UTF32)
(*UTF) set appropriate UTF mode for the library
in use
(*UCP) set PCRE_UCP (use Unicode properties for
\d etc)
Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce
the value of the limits set by the caller of pcre_exec(),
not increase them.
NEWLINE CONVENTION
These are recognized only at the very start of the pattern
or after option settings with a similar syntax.
(*CR) carriage return only
(*LF) linefeed only
(*CRLF) carriage return followed by linefeed
(*ANYCRLF) all three of the above
(*ANY) any Unicode newline sequence
WHAT \R MATCHES
These are recognized only at the very start of the pattern
or after option setting with a similar syntax.
(*BSR_ANYCRLF) CR, LF, or CRLF
(*BSR_UNICODE) any Unicode newline sequence
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
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\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 (Oni-
guruma)
\g'n' call subpattern by absolute number (Oni-
guruma)
\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
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(*FAIL) force backtrack; synonym (*F)
(*MARK:NAME) set name to be passed back; synonym
(*:NAME)
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 pat-
tern is not anchored.
(*COMMIT) overall failure, no advance of starting
point
(*PRUNE) advance to next starting character
(*PRUNE:NAME) equivalent to (*MARK:NAME)(*PRUNE)
(*SKIP) advance to current matching position
(*SKIP:NAME) advance to position corresponding to an
earlier
(*MARK:NAME); if not found, the (*SKIP) is
ignored
(*THEN) local failure, backtrack to next alterna-
tion
(*THEN:NAME) equivalent to (*MARK:NAME)(*THEN)
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: 08 January 2014
Copyright (c) 1997-2014 University of Cambridge.
PCRE 8.35 Last change: 08 January 2014 8
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