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<html><head><title>pcre2syntax specification</title></head><body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"><h1>pcre2syntax man page</h1><p>Return to the <a href="index.html">PCRE2 index page</a>.</p><p>This page is part of the PCRE2 HTML documentation. It was generatedautomatically from the original man page. If there is any nonsense in it,please consult the man page, in case the conversion went wrong.<br><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">BRACED ITEMS</a><li><a name="TOC4" href="#SEC4">ESCAPED CHARACTERS</a><li><a name="TOC5" href="#SEC5">CHARACTER TYPES</a><li><a name="TOC6" href="#SEC6">GENERAL CATEGORY PROPERTIES FOR \p and \P</a><li><a name="TOC7" href="#SEC7">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a><li><a name="TOC8" href="#SEC8">BINARY PROPERTIES FOR \p AND \P</a><li><a name="TOC9" href="#SEC9">SCRIPT MATCHING WITH \p AND \P</a><li><a name="TOC10" href="#SEC10">THE BIDI_CLASS PROPERTY FOR \p AND \P</a><li><a name="TOC11" href="#SEC11">CHARACTER CLASSES</a><li><a name="TOC12" href="#SEC12">QUANTIFIERS</a><li><a name="TOC13" href="#SEC13">ANCHORS AND SIMPLE ASSERTIONS</a><li><a name="TOC14" href="#SEC14">REPORTED MATCH POINT SETTING</a><li><a name="TOC15" href="#SEC15">ALTERNATION</a><li><a name="TOC16" href="#SEC16">CAPTURING</a><li><a name="TOC17" href="#SEC17">ATOMIC GROUPS</a><li><a name="TOC18" href="#SEC18">COMMENT</a><li><a name="TOC19" href="#SEC19">OPTION SETTING</a><li><a name="TOC20" href="#SEC20">NEWLINE CONVENTION</a><li><a name="TOC21" href="#SEC21">WHAT \R MATCHES</a><li><a name="TOC22" href="#SEC22">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a><li><a name="TOC23" href="#SEC23">NON-ATOMIC LOOKAROUND ASSERTIONS</a><li><a name="TOC24" href="#SEC24">SCRIPT RUNS</a><li><a name="TOC25" href="#SEC25">BACKREFERENCES</a><li><a name="TOC26" href="#SEC26">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a><li><a name="TOC27" href="#SEC27">CONDITIONAL PATTERNS</a><li><a name="TOC28" href="#SEC28">BACKTRACKING CONTROL</a><li><a name="TOC29" href="#SEC29">CALLOUTS</a><li><a name="TOC30" href="#SEC30">SEE ALSO</a><li><a name="TOC31" href="#SEC31">AUTHOR</a><li><a name="TOC32" href="#SEC32">REVISION</a></ul><br><a name="SEC1" href="#TOC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a><br><P>The full syntax and semantics of the regular expressions that are supported byPCRE2 are described in the<a href="pcre2pattern.html"><b>pcre2pattern</b></a>documentation. This document contains a quick-reference summary of the syntax.</P><br><a name="SEC2" href="#TOC1">QUOTING</a><br><P><pre> \x where x is non-alphanumeric is a literal x \Q...\E treat enclosed characters as literal</pre>Note that white space inside \Q...\E is always treated as literal, even ifPCRE2_EXTENDED is set, causing most other white space to be ignored.</P><br><a name="SEC3" href="#TOC1">BRACED ITEMS</a><br><P>With one exception, wherever brace characters { and } are required to enclosedata for constructions such as \g{2} or \k{name}, space and/or horizontal tabcharacters that follow { or precede } are allowed and are ignored. In the caseof quantifiers, they may also appear before or after the comma. The exceptionis \u{...} which is not Perl-compatible and is recognized only whenPCRE2_EXTRA_ALT_BSUX is set. This is an ECMAScript compatibility feature, andfollows ECMAScript's behaviour.</P><br><a name="SEC4" href="#TOC1">ESCAPED CHARACTERS</a><br><P>This table applies to ASCII and Unicode environments. An unrecognized escapesequence causes an error.<pre> \a alarm, that is, the BEL character (hex 07) \cx "control-x", where x is a non-control 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.. \N{U+hh..} character with Unicode code point hh.. (Unicode mode only) \xhh character with hex code hh \x{hh..} character with hex code hh..</pre>If PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX is set ("ALT_BSUX mode"), thefollowing are also recognized:<pre> \U the character "U" \uhhhh character with hex code hhhh \u{hh..} character with hex code hh.. but only for EXTRA_ALT_BSUX</pre>When \x is not followed by {, from zero to two hexadecimal digits are read,but in ALT_BSUX mode \x must be followed by two hexadecimal digits to berecognized as a hexadecimal escape; otherwise it matches a literal "x".Likewise, if \u (in ALT_BSUX mode) is not followed by four hexadecimal digitsor (in EXTRA_ALT_BSUX mode) a sequence of hex digits in curly brackets, itmatches a literal "u".</P><P>Note that \0dd is always an octal code. The treatment of backslash followed bya 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"><b>pcre2pattern</b></a>documentation, where details of escape processing in EBCDIC environments arealso given. \N{U+hh..} is synonymous with \x{hh..} in PCRE2 but is notsupported in EBCDIC environments. Note that \N not followed by an openingcurly bracket has a different meaning (see below).</P><br><a name="SEC5" href="#TOC1">CHARACTER TYPES</a><br><P><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{<i>xx</i>} a character with the <i>xx</i> property \P{<i>xx</i>} a character without the <i>xx</i> 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 middleof a UTF-8 or UTF-16 character. The application can lock out the use of \C bysetting the PCRE2_NEVER_BACKSLASH_C option. It is also possible to build PCRE2with the use of \C permanently disabled.</P><P>By default, \d, \s, and \w match only ASCII characters, even in UTF-8 modeor in the 16-bit and 32-bit libraries. However, if locale-specific matching ishappening, \s and \w may also match characters with code points in the range128-255. If the PCRE2_UCP option is set, the behaviour of these escapesequences is changed to use Unicode properties and they match many morecharacters, but there are some option settings that can restrict individualsequences to matching only ASCII characters.</P><P>Property descriptions in \p and \P are matched caselessly; hyphens,underscores, and white space are ignored, in accordance with Unicode's "loosematching" rules.</P><br><a name="SEC6" href="#TOC1">GENERAL CATEGORY PROPERTIES FOR \p and \P</a><br><P><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 Lc Ll, Lu, or Lt 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></P><br><a name="SEC7" href="#TOC1">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a><br><P><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 Universally-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 setat release 5.18.</P><br><a name="SEC8" href="#TOC1">BINARY PROPERTIES FOR \p AND \P</a><br><P>Unicode defines a number of binary properties, that is, properties whose onlyvalues are true or false. You can obtain a list of those that are recognized by\p and \P, along with their abbreviations, by running this command:<pre> pcre2test -LP</PRE></P><br><a name="SEC9" href="#TOC1">SCRIPT MATCHING WITH \p AND \P</a><br><P>Many script names and their 4-letter abbreviations are recognized in\p{sc:...} or \p{scx:...} items, or on their own with \p (and also \P ofcourse). You can obtain a list of these scripts by running this command:<pre> pcre2test -LS</PRE></P><br><a name="SEC10" href="#TOC1">THE BIDI_CLASS PROPERTY FOR \p AND \P</a><br><P><pre> \p{Bidi_Class:<class>} matches a character with the given class \p{BC:<class>} matches a character with the given class</pre>The recognized classes are:<pre> AL Arabic letter AN Arabic number B paragraph separator BN boundary neutral CS common separator EN European number ES European separator ET European terminator FSI first strong isolate L left-to-right LRE left-to-right embedding LRI left-to-right isolate LRO left-to-right override NSM non-spacing mark ON other neutral PDF pop directional format PDI pop directional isolate R right-to-left RLE right-to-left embedding RLI right-to-left isolate RLO right-to-left override S segment separator WS which space</PRE></P><br><a name="SEC11" href="#TOC1">CHARACTER CLASSES</a><br><P><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.</P><br><a name="SEC12" href="#TOC1">QUANTIFIERS</a><br><P><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 {,m} zero up to m, greedy {,m}+ zero up to m, possessive {,m}? zero up to m, lazy</PRE></P><br><a name="SEC13" href="#TOC1">ANCHORS AND SIMPLE ASSERTIONS</a><br><P><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></P><br><a name="SEC14" href="#TOC1">REPORTED MATCH POINT SETTING</a><br><P><pre> \K set reported start of match</pre>From release 10.38 \K is not permitted by default in lookaround assertions,for compatibility with Perl. However, if the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSKoption is set, the previous behaviour is re-enabled. When this option is set,\K is honoured in positive assertions, but ignored in negative ones.</P><br><a name="SEC15" href="#TOC1">ALTERNATION</a><br><P><pre> expr|expr|expr...</PRE></P><br><a name="SEC16" href="#TOC1">CAPTURING</a><br><P><pre> (...) capture group (?<name>...) named capture group (Perl) (?'name'...) named capture group (Perl) (?P<name>...) named capture group (Python) (?:...) non-capture group (?|...) non-capture group; reset group numbers for capture groups in each alternative</pre>In non-UTF modes, names may contain underscores and ASCII letters and digits;in UTF modes, any Unicode letters and Unicode decimal digits are permitted. Inboth cases, a name must not start with a digit.</P><br><a name="SEC17" href="#TOC1">ATOMIC GROUPS</a><br><P><pre> (?>...) atomic non-capture group (*atomic:...) atomic non-capture group</PRE></P><br><a name="SEC18" href="#TOC1">COMMENT</a><br><P><pre> (?#....) comment (not nestable)</PRE></P><br><a name="SEC19" href="#TOC1">OPTION SETTING</a><br><P>Changes of these options within a group are automatically cancelled at the endof the group.<pre> (?a) all ASCII options (?aD) restrict \d to ASCII in UCP mode (?aS) restrict \s to ASCII in UCP mode (?aW) restrict \w to ASCII in UCP mode (?aP) restrict all POSIX classes to ASCII in UCP mode (?aT) restrict POSIX digit classes to ASCII in UCP mode (?i) caseless (?J) allow duplicate named groups (?m) multiline (?n) no auto capture (?r) restrict caseless to either ASCII or non-ASCII (?s) single line (dotall) (?U) default ungreedy (lazy) (?x) ignore white space except in classes or \Q...\E (?xx) as (?x) but also ignore space and tab in classes (?-...) unset the given option(s) (?^) unset imnrsx options</pre>(?aP) implies (?aT) as well, though this has no additional effect. However, itmeans that (?-aP) is really (?-PT) which disables all ASCII restrictions forPOSIX classes.</P><P>Unsetting x or xx unsets both. Several options may be set at once, and amixture of setting and unsetting such as (?i-x) is allowed, but there may beonly one hyphen. Setting (but no unsetting) is allowed after (?^ for example(?^in). An option setting may appear at the start of a non-capture group, forexample (?i:...).</P><P>The following are recognized only at the very start of a pattern or after oneof the newline or \R options with similar syntax. More than one of them mayappear. 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 ofthe limits set by the caller of <b>pcre2_match()</b> or <b>pcre2_dfa_match()</b>,not increase them. LIMIT_RECURSION is an obsolete synonym for LIMIT_DEPTH. Theapplication can lock out the use of (*UTF) and (*UCP) by setting thePCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile time.</P><br><a name="SEC20" href="#TOC1">NEWLINE CONVENTION</a><br><P>These are recognized only at the very start of the pattern or after optionsettings 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></P><br><a name="SEC21" href="#TOC1">WHAT \R MATCHES</a><br><P>These are recognized only at the very start of the pattern or after optionsetting with a similar syntax.<pre> (*BSR_ANYCRLF) CR, LF, or CRLF (*BSR_UNICODE) any Unicode newline sequence</PRE></P><br><a name="SEC22" href="#TOC1">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a><br><P><pre> (?=...) ) (*pla:...) ) positive lookahead (*positive_lookahead:...) )
(?!...) ) (*nla:...) ) negative lookahead (*negative_lookahead:...) )
(?<=...) ) (*plb:...) ) positive lookbehind (*positive_lookbehind:...) )
(?<!...) ) (*nlb:...) ) negative lookbehind (*negative_lookbehind:...) )</pre>Each top-level branch of a lookbehind must have a limit for the number ofcharacters it matches. If any branch can match a variable number of characters,the maximum for each branch is limited to a value set by the caller of<b>pcre2_compile()</b> or defaulted. The default is set when PCRE2 is built(ultimate default 255). If every branch matches a fixed number of characters,the limit for each branch is 65535 characters.</P><br><a name="SEC23" href="#TOC1">NON-ATOMIC LOOKAROUND ASSERTIONS</a><br><P>These assertions are specific to PCRE2 and are not Perl-compatible.<pre> (?*...) ) (*napla:...) ) synonyms (*non_atomic_positive_lookahead:...) )
(?<*...) ) (*naplb:...) ) synonyms (*non_atomic_positive_lookbehind:...) )</PRE></P><br><a name="SEC24" href="#TOC1">SCRIPT RUNS</a><br><P><pre> (*script_run:...) ) script run, can be backtracked into (*sr:...) )
(*atomic_script_run:...) ) atomic script run (*asr:...) )</PRE></P><br><a name="SEC25" href="#TOC1">BACKREFERENCES</a><br><P><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></P><br><a name="SEC26" href="#TOC1">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a><br><P><pre> (?R) recurse whole pattern (?n) call subroutine by absolute number (?+n) call subroutine by relative number (?-n) call subroutine by relative number (?&name) call subroutine by name (Perl) (?P>name) call subroutine by name (Python) \g<name> call subroutine by name (Oniguruma) \g'name' call subroutine by name (Oniguruma) \g<n> call subroutine by absolute number (Oniguruma) \g'n' call subroutine by absolute number (Oniguruma) \g<+n> call subroutine by relative number (PCRE2 extension) \g'+n' call subroutine by relative number (PCRE2 extension) \g<-n> call subroutine by relative number (PCRE2 extension) \g'-n' call subroutine by relative number (PCRE2 extension)</PRE></P><br><a name="SEC27" href="#TOC1">CONDITIONAL PATTERNS</a><br><P><pre> (?(condition)yes-pattern) (?(condition)yes-pattern|no-pattern)
(?(n) absolute reference condition (?(+n) relative reference condition (PCRE2 extension) (?(-n) relative reference condition (PCRE2 extension) (?(<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 groups for reference (?(VERSION[>]=n.m) test PCRE2 version (?(assert) assertion condition</pre>Note the ambiguity of (?(R) and (?(Rn) which might be named referenceconditions or recursion tests. Such a condition is interpreted as a referencecondition if the relevant named group exists.</P><br><a name="SEC28" href="#TOC1">BACKTRACKING CONTROL</a><br><P>All backtracking control verbs may be in the form (*VERB:NAME). For (*MARK) thename is mandatory, for the others it is optional. (*SKIP) changes its behaviourif :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 theyare 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 toreach them. They all force a match failure, but they differ in what happensafterwards. Those that advance the start-of-match point do so only if thepattern 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 confinedto the subroutine call.</P><br><a name="SEC29" href="#TOC1">CALLOUTS</a><br><P><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 thestart and the end), and the starting delimiter { matched with the endingdelimiter }. To encode the ending delimiter within the string, double it.</P><br><a name="SEC30" href="#TOC1">SEE ALSO</a><br><P><b>pcre2pattern</b>(3), <b>pcre2api</b>(3), <b>pcre2callout</b>(3),<b>pcre2matching</b>(3), <b>pcre2</b>(3).</P><br><a name="SEC31" href="#TOC1">AUTHOR</a><br><P>Philip Hazel<br>Retired from University Computing Service<br>Cambridge, England.<br></P><br><a name="SEC32" href="#TOC1">REVISION</a><br><P>Last updated: 12 October 2023<br>Copyright © 1997-2023 University of Cambridge.<br><p>Return to the <a href="index.html">PCRE2 index page</a>.</p>
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