602 lines
22 KiB
HTML
602 lines
22 KiB
HTML
<html>
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<head>
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<title>pcre2syntax specification</title>
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</head>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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<h1>pcre2syntax man page</h1>
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<p>
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Return to the <a href="index.html">PCRE2 index page</a>.
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</p>
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<p>
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This page is part of the PCRE2 HTML documentation. It was generated
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automatically from the original man page. If there is any nonsense in it,
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please consult the man page, in case the conversion went wrong.
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<br>
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<ul>
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<li><a name="TOC1" href="#SEC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a>
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<li><a name="TOC2" href="#SEC2">QUOTING</a>
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<li><a name="TOC3" href="#SEC3">ESCAPED CHARACTERS</a>
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<li><a name="TOC4" href="#SEC4">CHARACTER TYPES</a>
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<li><a name="TOC5" href="#SEC5">GENERAL CATEGORY PROPERTIES FOR \p and \P</a>
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<li><a name="TOC6" href="#SEC6">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a>
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<li><a name="TOC7" href="#SEC7">BINARY PROPERTIES FOR \p AND \P</a>
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<li><a name="TOC8" href="#SEC8">SCRIPT MATCHING WITH \p AND \P</a>
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<li><a name="TOC9" href="#SEC9">THE BIDI_CLASS PROPERTY FOR \p AND \P</a>
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<li><a name="TOC10" href="#SEC10">CHARACTER CLASSES</a>
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<li><a name="TOC11" href="#SEC11">QUANTIFIERS</a>
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<li><a name="TOC12" href="#SEC12">ANCHORS AND SIMPLE ASSERTIONS</a>
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<li><a name="TOC13" href="#SEC13">REPORTED MATCH POINT SETTING</a>
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<li><a name="TOC14" href="#SEC14">ALTERNATION</a>
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<li><a name="TOC15" href="#SEC15">CAPTURING</a>
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<li><a name="TOC16" href="#SEC16">ATOMIC GROUPS</a>
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<li><a name="TOC17" href="#SEC17">COMMENT</a>
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<li><a name="TOC18" href="#SEC18">OPTION SETTING</a>
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<li><a name="TOC19" href="#SEC19">NEWLINE CONVENTION</a>
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<li><a name="TOC20" href="#SEC20">WHAT \R MATCHES</a>
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<li><a name="TOC21" href="#SEC21">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a>
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<li><a name="TOC22" href="#SEC22">NON-ATOMIC LOOKAROUND ASSERTIONS</a>
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<li><a name="TOC23" href="#SEC23">SCRIPT RUNS</a>
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<li><a name="TOC24" href="#SEC24">BACKREFERENCES</a>
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<li><a name="TOC25" href="#SEC25">SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)</a>
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<li><a name="TOC26" href="#SEC26">CONDITIONAL PATTERNS</a>
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<li><a name="TOC27" href="#SEC27">BACKTRACKING CONTROL</a>
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<li><a name="TOC28" href="#SEC28">CALLOUTS</a>
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<li><a name="TOC29" href="#SEC29">SEE ALSO</a>
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<li><a name="TOC30" href="#SEC30">AUTHOR</a>
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<li><a name="TOC31" href="#SEC31">REVISION</a>
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</ul>
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<br><a name="SEC1" href="#TOC1">PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY</a><br>
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<P>
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The full syntax and semantics of the regular expressions that are supported by
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PCRE2 are described in the
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<a href="pcre2pattern.html"><b>pcre2pattern</b></a>
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documentation. This document contains a quick-reference summary of the syntax.
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</P>
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<br><a name="SEC2" href="#TOC1">QUOTING</a><br>
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<P>
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<pre>
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\x where x is non-alphanumeric is a literal x
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\Q...\E treat enclosed characters as literal
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</PRE>
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</P>
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<br><a name="SEC3" href="#TOC1">ESCAPED CHARACTERS</a><br>
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<P>
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This table applies to ASCII and Unicode environments. An unrecognized escape
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sequence causes an error.
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<pre>
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\a alarm, that is, the BEL character (hex 07)
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\cx "control-x", where x is any ASCII printing character
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\e escape (hex 1B)
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\f form feed (hex 0C)
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\n newline (hex 0A)
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\r carriage return (hex 0D)
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\t tab (hex 09)
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\0dd character with octal code 0dd
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\ddd character with octal code ddd, or backreference
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\o{ddd..} character with octal code ddd..
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\N{U+hh..} character with Unicode code point hh.. (Unicode mode only)
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\xhh character with hex code hh
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\x{hh..} character with hex code hh..
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</pre>
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If PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX is set ("ALT_BSUX mode"), the
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following are also recognized:
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<pre>
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\U the character "U"
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\uhhhh character with hex code hhhh
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\u{hh..} character with hex code hh.. but only for EXTRA_ALT_BSUX
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</pre>
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When \x is not followed by {, from zero to two hexadecimal digits are read,
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but in ALT_BSUX mode \x must be followed by two hexadecimal digits to be
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recognized as a hexadecimal escape; otherwise it matches a literal "x".
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Likewise, if \u (in ALT_BSUX mode) is not followed by four hexadecimal digits
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or (in EXTRA_ALT_BSUX mode) a sequence of hex digits in curly brackets, it
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matches a literal "u".
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</P>
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<P>
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Note that \0dd is always an octal code. The treatment of backslash followed by
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a non-zero digit is complicated; for details see the section
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<a href="pcre2pattern.html#digitsafterbackslash">"Non-printing characters"</a>
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in the
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<a href="pcre2pattern.html"><b>pcre2pattern</b></a>
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documentation, where details of escape processing in EBCDIC environments are
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also given. \N{U+hh..} is synonymous with \x{hh..} in PCRE2 but is not
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supported in EBCDIC environments. Note that \N not followed by an opening
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curly bracket has a different meaning (see below).
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</P>
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<br><a name="SEC4" href="#TOC1">CHARACTER TYPES</a><br>
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<P>
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<pre>
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. any character except newline;
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in dotall mode, any character whatsoever
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\C one code unit, even in UTF mode (best avoided)
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\d a decimal digit
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\D a character that is not a decimal digit
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\h a horizontal white space character
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\H a character that is not a horizontal white space character
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\N a character that is not a newline
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\p{<i>xx</i>} a character with the <i>xx</i> property
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\P{<i>xx</i>} a character without the <i>xx</i> property
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\R a newline sequence
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\s a white space character
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\S a character that is not a white space character
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\v a vertical white space character
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\V a character that is not a vertical white space character
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\w a "word" character
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\W a "non-word" character
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\X a Unicode extended grapheme cluster
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</pre>
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\C is dangerous because it may leave the current matching point in the middle
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of a UTF-8 or UTF-16 character. The application can lock out the use of \C by
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setting the PCRE2_NEVER_BACKSLASH_C option. It is also possible to build PCRE2
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with the use of \C permanently disabled.
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</P>
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<P>
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By default, \d, \s, and \w match only ASCII characters, even in UTF-8 mode
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or in the 16-bit and 32-bit libraries. However, if locale-specific matching is
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happening, \s and \w may also match characters with code points in the range
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128-255. If the PCRE2_UCP option is set, the behaviour of these escape
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sequences is changed to use Unicode properties and they match many more
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characters.
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</P>
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<P>
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Property descriptions in \p and \P are matched caselessly; hyphens,
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underscores, and white space are ignored, in accordance with Unicode's "loose
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matching" rules.
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</P>
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<br><a name="SEC5" href="#TOC1">GENERAL CATEGORY PROPERTIES FOR \p and \P</a><br>
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<P>
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<pre>
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C Other
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Cc Control
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Cf Format
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Cn Unassigned
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Co Private use
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Cs Surrogate
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L Letter
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Ll Lower case letter
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Lm Modifier letter
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Lo Other letter
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Lt Title case letter
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Lu Upper case letter
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Lc Ll, Lu, or Lt
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L& Ll, Lu, or Lt
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M Mark
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Mc Spacing mark
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Me Enclosing mark
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Mn Non-spacing mark
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N Number
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Nd Decimal number
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Nl Letter number
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No Other number
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P Punctuation
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Pc Connector punctuation
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Pd Dash punctuation
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Pe Close punctuation
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Pf Final punctuation
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Pi Initial punctuation
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Po Other punctuation
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Ps Open punctuation
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S Symbol
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Sc Currency symbol
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Sk Modifier symbol
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Sm Mathematical symbol
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So Other symbol
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Z Separator
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Zl Line separator
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Zp Paragraph separator
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Zs Space separator
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</PRE>
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</P>
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<br><a name="SEC6" href="#TOC1">PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P</a><br>
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<P>
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<pre>
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Xan Alphanumeric: union of properties L and N
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Xps POSIX space: property Z or tab, NL, VT, FF, CR
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Xsp Perl space: property Z or tab, NL, VT, FF, CR
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Xuc Univerally-named character: one that can be
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represented by a Universal Character Name
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Xwd Perl word: property Xan or underscore
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</pre>
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Perl and POSIX space are now the same. Perl added VT to its space character set
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at release 5.18.
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</P>
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<br><a name="SEC7" href="#TOC1">BINARY PROPERTIES FOR \p AND \P</a><br>
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<P>
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Unicode defines a number of binary properties, that is, properties whose only
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values are true or false. You can obtain a list of those that are recognized by
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\p and \P, along with their abbreviations, by running this command:
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<pre>
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pcre2test -LP
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</PRE>
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</P>
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<br><a name="SEC8" href="#TOC1">SCRIPT MATCHING WITH \p AND \P</a><br>
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<P>
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Many script names and their 4-letter abbreviations are recognized in
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\p{sc:...} or \p{scx:...} items, or on their own with \p (and also \P of
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course). You can obtain a list of these scripts by running this command:
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<pre>
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pcre2test -LS
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</PRE>
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</P>
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<br><a name="SEC9" href="#TOC1">THE BIDI_CLASS PROPERTY FOR \p AND \P</a><br>
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<P>
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<pre>
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\p{Bidi_Class:<class>} matches a character with the given class
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\p{BC:<class>} matches a character with the given class
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</pre>
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The recognized classes are:
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<pre>
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AL Arabic letter
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AN Arabic number
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B paragraph separator
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BN boundary neutral
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CS common separator
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EN European number
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ES European separator
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ET European terminator
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FSI first strong isolate
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L left-to-right
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LRE left-to-right embedding
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LRI left-to-right isolate
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LRO left-to-right override
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NSM non-spacing mark
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ON other neutral
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PDF pop directional format
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PDI pop directional isolate
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R right-to-left
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RLE right-to-left embedding
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RLI right-to-left isolate
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RLO right-to-left override
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S segment separator
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WS which space
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</PRE>
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</P>
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<br><a name="SEC10" href="#TOC1">CHARACTER CLASSES</a><br>
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<P>
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<pre>
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[...] positive character class
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[^...] negative character class
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[x-y] range (can be used for hex characters)
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[[:xxx:]] positive POSIX named set
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[[:^xxx:]] negative POSIX named set
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alnum alphanumeric
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alpha alphabetic
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ascii 0-127
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blank space or tab
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cntrl control character
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digit decimal digit
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graph printing, excluding space
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lower lower case letter
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print printing, including space
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punct printing, excluding alphanumeric
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space white space
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upper upper case letter
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word same as \w
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xdigit hexadecimal digit
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</pre>
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In PCRE2, POSIX character set names recognize only ASCII characters by default,
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but some of them use Unicode properties if PCRE2_UCP is set. You can use
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\Q...\E inside a character class.
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</P>
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<br><a name="SEC11" href="#TOC1">QUANTIFIERS</a><br>
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<P>
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<pre>
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? 0 or 1, greedy
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?+ 0 or 1, possessive
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?? 0 or 1, lazy
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* 0 or more, greedy
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*+ 0 or more, possessive
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*? 0 or more, lazy
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+ 1 or more, greedy
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++ 1 or more, possessive
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+? 1 or more, lazy
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{n} exactly n
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{n,m} at least n, no more than m, greedy
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{n,m}+ at least n, no more than m, possessive
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{n,m}? at least n, no more than m, lazy
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{n,} n or more, greedy
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{n,}+ n or more, possessive
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{n,}? n or more, lazy
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</PRE>
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</P>
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<br><a name="SEC12" href="#TOC1">ANCHORS AND SIMPLE ASSERTIONS</a><br>
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<P>
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<pre>
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\b word boundary
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\B not a word boundary
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^ start of subject
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also after an internal newline in multiline mode
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(after any newline if PCRE2_ALT_CIRCUMFLEX is set)
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\A start of subject
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$ end of subject
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also before newline at end of subject
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also before internal newline in multiline mode
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\Z end of subject
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also before newline at end of subject
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\z end of subject
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\G first matching position in subject
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</PRE>
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</P>
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<br><a name="SEC13" href="#TOC1">REPORTED MATCH POINT SETTING</a><br>
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<P>
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<pre>
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\K set reported start of match
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</pre>
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From release 10.38 \K is not permitted by default in lookaround assertions,
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for compatibility with Perl. However, if the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK
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option is set, the previous behaviour is re-enabled. When this option is set,
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\K is honoured in positive assertions, but ignored in negative ones.
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</P>
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<br><a name="SEC14" href="#TOC1">ALTERNATION</a><br>
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<P>
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<pre>
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expr|expr|expr...
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</PRE>
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</P>
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<br><a name="SEC15" href="#TOC1">CAPTURING</a><br>
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<P>
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<pre>
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(...) capture group
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(?<name>...) named capture group (Perl)
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(?'name'...) named capture group (Perl)
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(?P<name>...) named capture group (Python)
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(?:...) non-capture group
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(?|...) non-capture group; reset group numbers for
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capture groups in each alternative
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</pre>
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In non-UTF modes, names may contain underscores and ASCII letters and digits;
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in UTF modes, any Unicode letters and Unicode decimal digits are permitted. In
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both cases, a name must not start with a digit.
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</P>
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<br><a name="SEC16" href="#TOC1">ATOMIC GROUPS</a><br>
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<P>
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<pre>
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(?>...) atomic non-capture group
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(*atomic:...) atomic non-capture group
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</PRE>
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</P>
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<br><a name="SEC17" href="#TOC1">COMMENT</a><br>
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<P>
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<pre>
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(?#....) comment (not nestable)
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</PRE>
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</P>
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<br><a name="SEC18" href="#TOC1">OPTION SETTING</a><br>
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<P>
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Changes of these options within a group are automatically cancelled at the end
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of the group.
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<pre>
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(?i) caseless
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(?J) allow duplicate named groups
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(?m) multiline
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(?n) no auto capture
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(?s) single line (dotall)
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(?U) default ungreedy (lazy)
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(?x) extended: ignore white space except in classes
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(?xx) as (?x) but also ignore space and tab in classes
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(?-...) unset option(s)
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(?^) unset imnsx options
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</pre>
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Unsetting x or xx unsets both. Several options may be set at once, and a
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mixture of setting and unsetting such as (?i-x) is allowed, but there may be
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only one hyphen. Setting (but no unsetting) is allowed after (?^ for example
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(?^in). An option setting may appear at the start of a non-capture group, for
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example (?i:...).
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</P>
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<P>
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The following are recognized only at the very start of a pattern or after one
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of the newline or \R options with similar syntax. More than one of them may
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appear. For the first three, d is a decimal number.
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<pre>
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(*LIMIT_DEPTH=d) set the backtracking limit to d
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(*LIMIT_HEAP=d) set the heap size limit to d * 1024 bytes
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(*LIMIT_MATCH=d) set the match limit to d
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(*NOTEMPTY) set PCRE2_NOTEMPTY when matching
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(*NOTEMPTY_ATSTART) set PCRE2_NOTEMPTY_ATSTART when matching
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(*NO_AUTO_POSSESS) no auto-possessification (PCRE2_NO_AUTO_POSSESS)
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(*NO_DOTSTAR_ANCHOR) no .* anchoring (PCRE2_NO_DOTSTAR_ANCHOR)
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(*NO_JIT) disable JIT optimization
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(*NO_START_OPT) no start-match optimization (PCRE2_NO_START_OPTIMIZE)
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(*UTF) set appropriate UTF mode for the library in use
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(*UCP) set PCRE2_UCP (use Unicode properties for \d etc)
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</pre>
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Note that LIMIT_DEPTH, LIMIT_HEAP, and LIMIT_MATCH can only reduce the value of
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the limits set by the caller of <b>pcre2_match()</b> or <b>pcre2_dfa_match()</b>,
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not increase them. LIMIT_RECURSION is an obsolete synonym for LIMIT_DEPTH. The
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application can lock out the use of (*UTF) and (*UCP) by setting the
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PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile time.
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</P>
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<br><a name="SEC19" href="#TOC1">NEWLINE CONVENTION</a><br>
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<P>
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These are recognized only at the very start of the pattern or after option
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settings with a similar syntax.
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<pre>
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(*CR) carriage return only
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(*LF) linefeed only
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(*CRLF) carriage return followed by linefeed
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(*ANYCRLF) all three of the above
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(*ANY) any Unicode newline sequence
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(*NUL) the NUL character (binary zero)
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</PRE>
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</P>
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<br><a name="SEC20" href="#TOC1">WHAT \R MATCHES</a><br>
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<P>
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These are recognized only at the very start of the pattern or after option
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setting with a similar syntax.
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<pre>
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(*BSR_ANYCRLF) CR, LF, or CRLF
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(*BSR_UNICODE) any Unicode newline sequence
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</PRE>
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</P>
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<br><a name="SEC21" href="#TOC1">LOOKAHEAD AND LOOKBEHIND ASSERTIONS</a><br>
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<P>
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<pre>
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(?=...) )
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(*pla:...) ) positive lookahead
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(*positive_lookahead:...) )
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|
|
(?!...) )
|
|
(*nla:...) ) negative lookahead
|
|
(*negative_lookahead:...) )
|
|
|
|
(?<=...) )
|
|
(*plb:...) ) positive lookbehind
|
|
(*positive_lookbehind:...) )
|
|
|
|
(?<!...) )
|
|
(*nlb:...) ) negative lookbehind
|
|
(*negative_lookbehind:...) )
|
|
</pre>
|
|
Each top-level branch of a lookbehind must be of a fixed length.
|
|
</P>
|
|
<br><a name="SEC22" 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="SEC23" 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="SEC24" 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="SEC25" 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="SEC26" href="#TOC1">CONDITIONAL PATTERNS</a><br>
|
|
<P>
|
|
<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 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="SEC27" 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="SEC28" 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="SEC29" 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="SEC30" href="#TOC1">AUTHOR</a><br>
|
|
<P>
|
|
Philip Hazel
|
|
<br>
|
|
Retired from University Computing Service
|
|
<br>
|
|
Cambridge, England.
|
|
<br>
|
|
</P>
|
|
<br><a name="SEC31" href="#TOC1">REVISION</a><br>
|
|
<P>
|
|
Last updated: 12 January 2022
|
|
<br>
|
|
Copyright © 1997-2022 University of Cambridge.
|
|
<br>
|
|
<p>
|
|
Return to the <a href="index.html">PCRE2 index page</a>.
|
|
</p>
|