| <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 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. |
| <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 by |
| PCRE2 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 if |
| PCRE2_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 enclose |
| data for constructions such as \g{2} or \k{name}, space and/or horizontal tab |
| characters that follow { or precede } are allowed and are ignored. In the case |
| of quantifiers, they may also appear before or after the comma. The exception |
| is \u{...} which is not Perl-compatible and is recognized only when |
| PCRE2_EXTRA_ALT_BSUX is set. This is an ECMAScript compatibility feature, and |
| follows 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 escape |
| sequence 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"), the |
| following 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 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 |
| or (in EXTRA_ALT_BSUX mode) a sequence of hex digits in curly brackets, it |
| matches a literal "u". |
| </P> |
| <P> |
| 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"><b>pcre2pattern</b></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). |
| </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 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. |
| </P> |
| <P> |
| 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, but there are some option settings that can restrict individual |
| sequences 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 "loose |
| matching" 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 set |
| at 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 only |
| values 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 of |
| course). 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_BSK |
| option 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. In |
| both 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 end |
| of 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, it |
| means that (?-aP) is really (?-PT) which disables all ASCII restrictions for |
| POSIX classes. |
| </P> |
| <P> |
| 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-capture group, for |
| example (?i:...). |
| </P> |
| <P> |
| 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 <b>pcre2_match()</b> or <b>pcre2_dfa_match()</b>, |
| 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. |
| </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 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> |
| </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 option |
| setting 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 of |
| characters 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 reference |
| conditions or recursion tests. Such a condition is interpreted as a reference |
| condition 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) 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. |
| </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 the |
| start and the end), and the starting delimiter { matched with the ending |
| delimiter }. 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> |