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pcresyntax(3)                                                    pcresyntax(3)




NAME

       PCRE - Perl-compatible regular expressions


PCRE REGULAR EXPRESSION SYNTAX SUMMARY


       The  full syntax and semantics of the regular expressions that are sup-
       ported by PCRE are described in  the  pcrepattern  documentation.  This
       document contains a quick-reference summary of the syntax.


QUOTING


         \x         where x is non-alphanumeric is a literal x
         \Q...\E    treat enclosed characters as literal


CHARACTERS


         \a         alarm, that is, the BEL character (hex 07)
         \cx        "control-x", where x is any ASCII character
         \e         escape (hex 1B)
         \f         form feed (hex 0C)
         \n         newline (hex 0A)
         \r         carriage return (hex 0D)
         \t         tab (hex 09)
         \0dd       character with octal code 0dd
         \ddd       character with octal code ddd, or backreference
         \o{ddd..}  character with octal code ddd..
         \xhh       character with hex code hh
         \x{hhh..}  character with hex code hhh..

       Note that \0dd is always an octal code, and that \8 and \9 are the lit-
       eral characters "8" and "9".


CHARACTER TYPES


         .          any character except newline;
                      in dotall mode, any character whatsoever
         \C         one data unit, even in UTF mode (best avoided)
         \d         a decimal digit
         \D         a character that is not a decimal digit
         \h         a horizontal white space character
         \H         a character that is not a horizontal white space character
         \N         a character that is not a newline
         \p{xx}     a character with the xx property
         \P{xx}     a character without the xx property
         \R         a newline sequence
         \s         a white space character
         \S         a character that is not a white space character
         \v         a vertical white space character
         \V         a character that is not a vertical white space character
         \w         a "word" character
         \W         a "non-word" character
         \X         a Unicode extended grapheme cluster

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


GENERAL CATEGORY PROPERTIES FOR \p and \P


         C          Other
         Cc         Control
         Cf         Format
         Cn         Unassigned
         Co         Private use
         Cs         Surrogate

         L          Letter
         Ll         Lower case letter
         Lm         Modifier letter
         Lo         Other letter
         Lt         Title case letter
         Lu         Upper case letter
         L&         Ll, Lu, or Lt

         M          Mark
         Mc         Spacing mark
         Me         Enclosing mark
         Mn         Non-spacing mark

         N          Number
         Nd         Decimal number
         Nl         Letter number
         No         Other number

         P          Punctuation
         Pc         Connector punctuation
         Pd         Dash punctuation
         Pe         Close punctuation
         Pf         Final punctuation
         Pi         Initial punctuation
         Po         Other punctuation
         Ps         Open punctuation

         S          Symbol
         Sc         Currency symbol
         Sk         Modifier symbol
         Sm         Mathematical symbol
         So         Other symbol

         Z          Separator
         Zl         Line separator
         Zp         Paragraph separator
         Zs         Space separator


PCRE SPECIAL CATEGORY PROPERTIES FOR \p and \P


         Xan        Alphanumeric: union of properties L and N
         Xps        POSIX space: property Z or tab, NL, VT, FF, CR
         Xsp        Perl space: property Z or tab, NL, VT, FF, CR
         Xuc        Univerally-named character: one that can be
                      represented by a Universal Character Name
         Xwd        Perl word: property Xan or underscore

       Perl and POSIX space are now the same. Perl added VT to its space char-
       acter set at release 5.18 and PCRE changed at release 8.34.


SCRIPT NAMES FOR \p AND \P


       Arabic,  Armenian, Avestan, Balinese, Bamum, Bassa_Vah, Batak, Bengali,
       Bopomofo, Brahmi, Braille, Buginese, Buhid,  Canadian_Aboriginal,  Car-
       ian, Caucasian_Albanian, Chakma, Cham, Cherokee, Common, Coptic, Cunei-
       form, Cypriot, Cyrillic, Deseret, Devanagari, Duployan, Egyptian_Hiero-
       glyphs,  Elbasan,  Ethiopic,  Georgian,  Glagolitic,  Gothic,  Grantha,
       Greek, Gujarati, Gurmukhi,  Han,  Hangul,  Hanunoo,  Hebrew,  Hiragana,
       Imperial_Aramaic,     Inherited,     Inscriptional_Pahlavi,    Inscrip-
       tional_Parthian,  Javanese,  Kaithi,   Kannada,   Katakana,   Kayah_Li,
       Kharoshthi,  Khmer,  Khojki, Khudawadi, Lao, Latin, Lepcha, Limbu, Lin-
       ear_A, Linear_B, Lisu, Lycian, Lydian,  Mahajani,  Malayalam,  Mandaic,
       Manichaean,      Meetei_Mayek,     Mende_Kikakui,     Meroitic_Cursive,
       Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro,  Myanmar,  Nabataean,
       New_Tai_Lue,   Nko,  Ogham,  Ol_Chiki,  Old_Italic,  Old_North_Arabian,
       Old_Permic, Old_Persian, Old_South_Arabian, Old_Turkic, Oriya, Osmanya,
       Pahawh_Hmong,    Palmyrene,    Pau_Cin_Hau,    Phags_Pa,    Phoenician,
       Psalter_Pahlavi, Rejang, Runic, Samaritan,  Saurashtra,  Sharada,  Sha-
       vian,  Siddham, Sinhala, Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac,
       Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet,  Takri,  Tamil,  Telugu,
       Thaana,  Thai,  Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi,
       Yi.


CHARACTER CLASSES


         [...]       positive character class
         [^...]      negative character class
         [x-y]       range (can be used for hex characters)
         [[:xxx:]]   positive POSIX named set
         [[:^xxx:]]  negative POSIX named set

         alnum       alphanumeric
         alpha       alphabetic
         ascii       0-127
         blank       space or tab
         cntrl       control character
         digit       decimal digit
         graph       printing, excluding space
         lower       lower case letter
         print       printing, including space
         punct       printing, excluding alphanumeric
         space       white space
         upper       upper case letter
         word        same as \w
         xdigit      hexadecimal digit

       In PCRE, POSIX character set names recognize only ASCII  characters  by
       default,  but  some  of them use Unicode properties if PCRE_UCP is set.
       You can use \Q...\E inside a character class.


QUANTIFIERS


         ?           0 or 1, greedy
         ?+          0 or 1, possessive
         ??          0 or 1, lazy
         *           0 or more, greedy
         *+          0 or more, possessive
         *?          0 or more, lazy
         +           1 or more, greedy
         ++          1 or more, possessive
         +?          1 or more, lazy
         {n}         exactly n
         {n,m}       at least n, no more than m, greedy
         {n,m}+      at least n, no more than m, possessive
         {n,m}?      at least n, no more than m, lazy
         {n,}        n or more, greedy
         {n,}+       n or more, possessive
         {n,}?       n or more, lazy


ANCHORS AND SIMPLE ASSERTIONS


         \b          word boundary
         \B          not a word boundary
         ^           start of subject
                      also after internal newline in multiline mode
         \A          start of subject
         $           end of subject
                      also before newline at end of subject
                      also before internal newline in multiline mode
         \Z          end of subject
                      also before newline at end of subject
         \z          end of subject
         \G          first matching position in subject


MATCH POINT RESET


         \K          reset start of match

       \K is honoured in positive assertions, but ignored in negative ones.


ALTERNATION


         expr|expr|expr...


CAPTURING


         (...)           capturing group
         (?<name>...)    named capturing group (Perl)
         (?'name'...)    named capturing group (Perl)
         (?P<name>...)   named capturing group (Python)
         (?:...)         non-capturing group
         (?|...)         non-capturing group; reset group numbers for
                          capturing groups in each alternative


ATOMIC GROUPS


         (?>...)         atomic, non-capturing group


COMMENT


         (?#....)        comment (not nestable)


OPTION SETTING


         (?i)            caseless
         (?J)            allow duplicate names
         (?m)            multiline
         (?s)            single line (dotall)
         (?U)            default ungreedy (lazy)
         (?x)            extended (ignore white space)
         (?-...)         unset option(s)

       The following are recognized only at the very start  of  a  pattern  or
       after  one  of the newline or \R options with similar syntax. More than
       one of them may appear.

         (*LIMIT_MATCH=d) set the match limit to d (decimal number)
         (*LIMIT_RECURSION=d) set the recursion limit to d (decimal number)
         (*NO_AUTO_POSSESS) no auto-possessification (PCRE_NO_AUTO_POSSESS)
         (*NO_START_OPT) no start-match optimization (PCRE_NO_START_OPTIMIZE)
         (*UTF8)         set UTF-8 mode: 8-bit library (PCRE_UTF8)
         (*UTF16)        set UTF-16 mode: 16-bit library (PCRE_UTF16)
         (*UTF32)        set UTF-32 mode: 32-bit library (PCRE_UTF32)
         (*UTF)          set appropriate UTF mode for the library in use
         (*UCP)          set PCRE_UCP (use Unicode properties for \d etc)

       Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value  of
       the limits set by the caller of pcre_exec(), not increase them.


NEWLINE CONVENTION


       These  are  recognized  only  at the very start of the pattern or after
       option settings with a similar syntax.

         (*CR)           carriage return only
         (*LF)           linefeed only
         (*CRLF)         carriage return followed by linefeed
         (*ANYCRLF)      all three of the above
         (*ANY)          any Unicode newline sequence


WHAT \R MATCHES


       These are recognized only at the very start of  the  pattern  or  after
       option setting with a similar syntax.

         (*BSR_ANYCRLF)  CR, LF, or CRLF
         (*BSR_UNICODE)  any Unicode newline sequence


LOOKAHEAD AND LOOKBEHIND ASSERTIONS


         (?=...)         positive look ahead
         (?!...)         negative look ahead
         (?<=...)        positive look behind
         (?<!...)        negative look behind

       Each top-level branch of a look behind must be of a fixed length.


BACKREFERENCES


         \n              reference by number (can be ambiguous)
         \gn             reference by number
         \g{n}           reference by number
         \g{-n}          relative reference by number
         \k<name>        reference by name (Perl)
         \k'name'        reference by name (Perl)
         \g{name}        reference by name (Perl)
         \k{name}        reference by name (.NET)
         (?P=name)       reference by name (Python)


SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)


         (?R)            recurse whole pattern
         (?n)            call subpattern by absolute number
         (?+n)           call subpattern by relative number
         (?-n)           call subpattern by relative number
         (?&name)        call subpattern by name (Perl)
         (?P>name)       call subpattern by name (Python)
         \g<name>        call subpattern by name (Oniguruma)
         \g'name'        call subpattern by name (Oniguruma)
         \g<n>           call subpattern by absolute number (Oniguruma)
         \g'n'           call subpattern by absolute number (Oniguruma)
         \g<+n>          call subpattern by relative number (PCRE extension)
         \g'+n'          call subpattern by relative number (PCRE extension)
         \g<-n>          call subpattern by relative number (PCRE extension)
         \g'-n'          call subpattern by relative number (PCRE extension)


CONDITIONAL PATTERNS


         (?(condition)yes-pattern)
         (?(condition)yes-pattern|no-pattern)

         (?(n)...        absolute reference condition
         (?(+n)...       relative reference condition
         (?(-n)...       relative reference condition
         (?(<name>)...   named reference condition (Perl)
         (?('name')...   named reference condition (Perl)
         (?(name)...     named reference condition (PCRE)
         (?(R)...        overall recursion condition
         (?(Rn)...       specific group recursion condition
         (?(R&name)...   specific recursion condition
         (?(DEFINE)...   define subpattern for reference
         (?(assert)...   assertion condition


BACKTRACKING CONTROL


       The following act immediately they are reached:

         (*ACCEPT)       force successful match
         (*FAIL)         force backtrack; synonym (*F)
         (*MARK:NAME)    set name to be passed back; synonym (*:NAME)

       The  following  act only when a subsequent match failure causes a back-
       track 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.

         (*COMMIT)       overall failure, no advance of starting point
         (*PRUNE)        advance to next starting character
         (*PRUNE:NAME)   equivalent to (*MARK:NAME)(*PRUNE)
         (*SKIP)         advance to current matching position
         (*SKIP:NAME)    advance to position corresponding to an earlier
                         (*MARK:NAME); if not found, the (*SKIP) is ignored
         (*THEN)         local failure, backtrack to next alternation
         (*THEN:NAME)    equivalent to (*MARK:NAME)(*THEN)


CALLOUTS


         (?C)      callout
         (?Cn)     callout with data n


SEE ALSO


       pcrepattern(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcre(3).


AUTHOR


       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.


REVISION


       Last updated: 08 January 2014
       Copyright (c) 1997-2014 University of Cambridge.



PCRE 8.35                       08 January 2014                  pcresyntax(3)

pcre 8.36 - Generated Fri Oct 10 11:41:02 CDT 2014
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