Default page

Edit File: pcre2syntax.html

<html>
<head>
<title>pcre2syntax specification</title>
</head>
<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
<h1>pcre2syntax man page</h1>

Return to the <a href="index.html">PCRE2 index page</a>.


This page is part of the PCRE2 HTML documentation. It was generated
automatically from the original man page. If there is any nonsense in it,
please consult the man page, in case the conversion went wrong.
 
<ul>
<li><a name="TOC1" href="#SEC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a>
<li><a name="TOC2" href="#SEC2">QUOTING</a>
<li><a name="TOC3" href="#SEC3">ESCAPED CHARACTERS</a>
<li><a name="TOC4" href="#SEC4">CHARACTER TYPES</a>
<li><a name="TOC5" href="#SEC5">GENERAL CATEGORY PROPERTIES FOR \p and \P</a>
<li><a name="TOC6" href="#SEC6">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a>
<li><a name="TOC7" href="#SEC7">SCRIPT NAMES FOR \p AND \P</a>
<li><a name="TOC8" href="#SEC8">CHARACTER CLASSES</a>
<li><a name="TOC9" href="#SEC9">QUANTIFIERS</a>
<li><a name="TOC10" href="#SEC10">ANCHORS AND SIMPLE ASSERTIONS</a>
<li><a name="TOC11" href="#SEC11">REPORTED MATCH POINT SETTING</a>
<li><a name="TOC12" href="#SEC12">ALTERNATION</a>
<li><a name="TOC13" href="#SEC13">CAPTURING</a>
<li><a name="TOC14" href="#SEC14">ATOMIC GROUPS</a>
<li><a name="TOC15" href="#SEC15">COMMENT</a>
<li><a name="TOC16" href="#SEC16">OPTION SETTING</a>
<li><a name="TOC17" href="#SEC17">NEWLINE CONVENTION</a>
<li><a name="TOC18" href="#SEC18">WHAT \R MATCHES</a>
<li><a name="TOC19" href="#SEC19">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a>
<li><a name="TOC20" href="#SEC20">BACKREFERENCES</a>
<li><a name="TOC21" href="#SEC21">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a>
<li><a name="TOC22" href="#SEC22">CONDITIONAL PATTERNS</a>
<li><a name="TOC23" href="#SEC23">BACKTRACKING CONTROL</a>
<li><a name="TOC24" href="#SEC24">CALLOUTS</a>
<li><a name="TOC25" href="#SEC25">SEE ALSO</a>
<li><a name="TOC26" href="#SEC26">AUTHOR</a>
<li><a name="TOC27" href="#SEC27">REVISION</a>
</ul>
 <a name="SEC1" href="#TOC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a> 

The full syntax and semantics of the regular expressions that are supported by
PCRE2 are described in the
<a href="pcre2pattern.html">pcre2pattern</a>
documentation. This document contains a quick-reference summary of the syntax.

 <a name="SEC2" href="#TOC1">QUOTING</a> 

<pre>
 \x where x is non-alphanumeric is a literal x
 \Q...\E treat enclosed characters as literal
</PRE>

 <a name="SEC3" href="#TOC1">ESCAPED CHARACTERS</a> 

This table applies to ASCII and Unicode environments.
<pre>
 \a alarm, that is, the BEL character (hex 07)
 \cx "control-x", where x is any ASCII printing 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..
 \U "U" if PCRE2_ALT_BSUX is set (otherwise is an error)
 \N{U+hh..} character with Unicode code point hh.. (Unicode mode only)
 \uhhhh character with hex code hhhh (if PCRE2_ALT_BSUX is set)
 \xhh character with hex code hh
 \x{hh..} character with hex code hh..
</pre>
Note that \0dd is always an octal code. The treatment of backslash followed by
a non-zero digit is complicated; for details see the section
<a href="pcre2pattern.html#digitsafterbackslash">"Non-printing characters"</a>
in the
<a href="pcre2pattern.html">pcre2pattern</a>
documentation, where details of escape processing in EBCDIC environments are
also given. \N{U+hh..} is synonymous with \x{hh..} in PCRE2 but is not
supported in EBCDIC environments. Note that \N not followed by an opening
curly bracket has a different meaning (see below).


When \x is not followed by {, from zero to two hexadecimal digits are read,
but if PCRE2_ALT_BSUX is set, \x must be followed by two hexadecimal digits to
be recognized as a hexadecimal escape; otherwise it matches a literal "x".
Likewise, if \u (in ALT_BSUX mode) is not followed by four hexadecimal digits,
it matches a literal "u".

 <a name="SEC4" href="#TOC1">CHARACTER TYPES</a> 

<pre>
 . any character except newline;
 in dotall mode, any character whatsoever
 \C one code 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
 \w a "word" character
 \W a "non-word" character
 \X a Unicode extended grapheme cluster
</pre>
\C is dangerous because it may leave the current matching point in the middle
of a UTF-8 or UTF-16 character. The application can lock out the use of \C by
setting the PCRE2_NEVER_BACKSLASH_C option. It is also possible to build PCRE2
with the use of \C permanently disabled.


By default, \d, \s, and \w match only ASCII characters, even in UTF-8 mode
or in the 16-bit and 32-bit libraries. However, if locale-specific matching is
happening, \s and \w may also match characters with code points in the range
128-255. If the PCRE2_UCP option is set, the behaviour of these escape
sequences is changed to use Unicode properties and they match many more
characters.

 <a name="SEC5" href="#TOC1">GENERAL CATEGORY PROPERTIES FOR \p and \P</a> 

<pre>
 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
</PRE>

 <a name="SEC6" href="#TOC1">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a> 

<pre>
 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
</pre>
Perl and POSIX space are now the same. Perl added VT to its space character set
at release 5.18.

 <a name="SEC7" href="#TOC1">SCRIPT NAMES FOR \p AND \P</a> 

Adlam,
Ahom,
Anatolian_Hieroglyphs,
Arabic,
Armenian,
Avestan,
Balinese,
Bamum,
Bassa_Vah,
Batak,
Bengali,
Bhaiksuki,
Bopomofo,
Brahmi,
Braille,
Buginese,
Buhid,
Canadian_Aboriginal,
Carian,
Caucasian_Albanian,
Chakma,
Cham,
Cherokee,
Common,
Coptic,
Cuneiform,
Cypriot,
Cyrillic,
Deseret,
Devanagari,
Dogra,
Duployan,
Egyptian_Hieroglyphs,
Elbasan,
Ethiopic,
Georgian,
Glagolitic,
Gothic,
Grantha,
Greek,
Gujarati,
Gunjala_Gondi,
Gurmukhi,
Han,
Hangul,
Hanifi_Rohingya,
Hanunoo,
Hatran,
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,
Makasar,
Malayalam,
Mandaic,
Manichaean,
Marchen,
Masaram_Gondi,
Medefaidrin,
Meetei_Mayek,
Mende_Kikakui,
Meroitic_Cursive,
Meroitic_Hieroglyphs,
Miao,
Modi,
Mongolian,
Mro,
Multani,
Myanmar,
Nabataean,
New_Tai_Lue,
Newa,
Nko,
Nushu,
Ogham,
Ol_Chiki,
Old_Hungarian,
Old_Italic,
Old_North_Arabian,
Old_Permic,
Old_Persian,
Old_Sogdian,
Old_South_Arabian,
Old_Turkic,
Oriya,
Osage,
Osmanya,
Pahawh_Hmong,
Palmyrene,
Pau_Cin_Hau,
Phags_Pa,
Phoenician,
Psalter_Pahlavi,
Rejang,
Runic,
Samaritan,
Saurashtra,
Sharada,
Shavian,
Siddham,
SignWriting,
Sinhala,
Sogdian,
Sora_Sompeng,
Soyombo,
Sundanese,
Syloti_Nagri,
Syriac,
Tagalog,
Tagbanwa,
Tai_Le,
Tai_Tham,
Tai_Viet,
Takri,
Tamil,
Tangut,
Telugu,
Thaana,
Thai,
Tibetan,
Tifinagh,
Tirhuta,
Ugaritic,
Vai,
Warang_Citi,
Yi,
Zanabazar_Square.

 <a name="SEC8" href="#TOC1">CHARACTER CLASSES</a> 

<pre>
 [...] 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
</pre>
In PCRE2, POSIX character set names recognize only ASCII characters by default,
but some of them use Unicode properties if PCRE2_UCP is set. You can use
\Q...\E inside a character class.

 <a name="SEC9" href="#TOC1">QUANTIFIERS</a> 

<pre>
 ? 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
</PRE>

 <a name="SEC10" href="#TOC1">ANCHORS AND SIMPLE ASSERTIONS</a> 

<pre>
 \b word boundary
 \B not a word boundary
 ^ start of subject
 also after an internal newline in multiline mode
 (after any newline if PCRE2_ALT_CIRCUMFLEX is set)
 \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
</PRE>

 <a name="SEC11" href="#TOC1">REPORTED MATCH POINT SETTING</a> 

<pre>
 \K set reported start of match
</pre>
\K is honoured in positive assertions, but ignored in negative ones.

 <a name="SEC12" href="#TOC1">ALTERNATION</a> 

<pre>
 expr|expr|expr...
</PRE>

 <a name="SEC13" href="#TOC1">CAPTURING</a> 

<pre>
 (...) 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
</PRE>

 <a name="SEC14" href="#TOC1">ATOMIC GROUPS</a> 

<pre>
 (?>...) atomic, non-capturing group
</PRE>

 <a name="SEC15" href="#TOC1">COMMENT</a> 

<pre>
 (?#....) comment (not nestable)
</PRE>

 <a name="SEC16" href="#TOC1">OPTION SETTING</a> 

Changes of these options within a group are automatically cancelled at the end
of the group.
<pre>
 (?i) caseless
 (?J) allow duplicate names
 (?m) multiline
 (?n) no auto capture
 (?s) single line (dotall)
 (?U) default ungreedy (lazy)
 (?x) extended: ignore white space except in classes
 (?xx) as (?x) but also ignore space and tab in classes
 (?-...) unset option(s)
 (?^) unset imnsx options
</pre>
Unsetting x or xx unsets both. Several options may be set at once, and a
mixture of setting and unsetting such as (?i-x) is allowed, but there may be
only one hyphen. Setting (but no unsetting) is allowed after (?^ for example
(?^in). An option setting may appear at the start of a non-capturing group, for
example (?i:...).


The following are recognized only at the very start of a pattern or after one
of the newline or \R options with similar syntax. More than one of them may
appear. For the first three, d is a decimal number.
<pre>
 (*LIMIT_DEPTH=d) set the backtracking limit to d
 (*LIMIT_HEAP=d) set the heap size limit to d * 1024 bytes
 (*LIMIT_MATCH=d) set the match limit to d
 (*NOTEMPTY) set PCRE2_NOTEMPTY when matching
 (*NOTEMPTY_ATSTART) set PCRE2_NOTEMPTY_ATSTART when matching
 (*NO_AUTO_POSSESS) no auto-possessification (PCRE2_NO_AUTO_POSSESS)
 (*NO_DOTSTAR_ANCHOR) no .* anchoring (PCRE2_NO_DOTSTAR_ANCHOR)
 (*NO_JIT) disable JIT optimization
 (*NO_START_OPT) no start-match optimization (PCRE2_NO_START_OPTIMIZE)
 (*UTF) set appropriate UTF mode for the library in use
 (*UCP) set PCRE2_UCP (use Unicode properties for \d etc)
</pre>
Note that LIMIT_DEPTH, LIMIT_HEAP, and LIMIT_MATCH can only reduce the value of
the limits set by the caller of pcre2_match() or pcre2_dfa_match(),
not increase them. LIMIT_RECURSION is an obsolete synonym for LIMIT_DEPTH. The
application can lock out the use of (*UTF) and (*UCP) by setting the
PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile time.

 <a name="SEC17" href="#TOC1">NEWLINE CONVENTION</a> 

These are recognized only at the very start of the pattern or after option
settings with a similar syntax.
<pre>
 (*CR) carriage return only
 (*LF) linefeed only
 (*CRLF) carriage return followed by linefeed
 (*ANYCRLF) all three of the above
 (*ANY) any Unicode newline sequence
 (*NUL) the NUL character (binary zero)
</PRE>

 <a name="SEC18" href="#TOC1">WHAT \R MATCHES</a> 

These are recognized only at the very start of the pattern or after option
setting with a similar syntax.
<pre>
 (*BSR_ANYCRLF) CR, LF, or CRLF
 (*BSR_UNICODE) any Unicode newline sequence
</PRE>

 <a name="SEC19" href="#TOC1">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a> 

<pre>
 (?=...) positive look ahead
 (?!...) negative look ahead
 (?<=...) positive look behind
 (?<!...) negative look behind
</pre>
Each top-level branch of a look behind must be of a fixed length.

 <a name="SEC20" href="#TOC1">BACKREFERENCES</a> 

<pre>
 \n reference by number (can be ambiguous)
 \gn reference by number
 \g{n} reference by number
 \g+n relative reference by number (PCRE2 extension)
 \g-n relative reference by number
 \g{+n} relative reference by number (PCRE2 extension)
 \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)
</PRE>

 <a name="SEC21" href="#TOC1">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a> 

<pre>
 (?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 (PCRE2 extension)
 \g'+n' call subpattern by relative number (PCRE2 extension)
 \g<-n> call subpattern by relative number (PCRE2 extension)
 \g'-n' call subpattern by relative number (PCRE2 extension)
</PRE>

 <a name="SEC22" href="#TOC1">CONDITIONAL PATTERNS</a> 

<pre>
 (?(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 (PCRE2, deprecated)
 (?(R) overall recursion condition
 (?(Rn) specific numbered group recursion condition
 (?(R&name) specific named group recursion condition
 (?(DEFINE) define subpattern for reference
 (?(VERSION[>]=n.m) test PCRE2 version
 (?(assert) assertion condition
</pre>
Note the ambiguity of (?(R) and (?(Rn) which might be named reference
conditions or recursion tests. Such a condition is interpreted as a reference
condition if the relevant named group exists.

 <a name="SEC23" href="#TOC1">BACKTRACKING CONTROL</a> 

All backtracking control verbs may be in the form (*VERB:NAME). For (*MARK) the
name is mandatory, for the others it is optional. (*SKIP) changes its behaviour
if :NAME is present. The others just set a name for passing back to the caller,
but this is not a name that (*SKIP) can see. The following act immediately they
are reached:
<pre>
 (*ACCEPT) force successful match
 (*FAIL) force backtrack; synonym (*F)
 (*MARK:NAME) set name to be passed back; synonym (*:NAME)
</pre>
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.
<pre>
 (*COMMIT) overall failure, no advance of starting point
 (*PRUNE) advance to next starting character
 (*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 alternation
</pre>
The effect of one of these verbs in a group called as a subroutine is confined
to the subroutine call.

 <a name="SEC24" href="#TOC1">CALLOUTS</a> 

<pre>
 (?C) callout (assumed number 0)
 (?Cn) callout with numerical data n
 (?C"text") callout with string data
</pre>
The allowed string delimiters are ` ' " ^ % # $ (which are the same for the
start and the end), and the starting delimiter { matched with the ending
delimiter }. To encode the ending delimiter within the string, double it.

 <a name="SEC25" href="#TOC1">SEE ALSO</a> 

pcre2pattern(3), pcre2api(3), pcre2callout(3),
pcre2matching(3), pcre2(3).

 <a name="SEC26" href="#TOC1">AUTHOR</a> 

Philip Hazel
 
University Computing Service
 
Cambridge, England.
 

 <a name="SEC27" href="#TOC1">REVISION</a> 

Last updated: 02 September 2018
 
Copyright © 1997-2018 University of Cambridge.
 

Return to the <a href="index.html">PCRE2 index page</a>.