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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)
         \ddd       character with octal code ddd, or backreference
         \xhh       character with hex code hh
         \x{hhh..}  character with hex code hhh..


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

       In  PCRE,  by  default, \d, \D, \s, \S, \w, and \W recognize only ASCII
       characters, even in a UTF mode. However, this can be changed by setting
       the PCRE_UCP option.


GENERAL CATEGORY PROPERTIES FOR \p and \P


         C          Other
         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, FF, CR
         Xwd        Perl word: property Xan or underscore


SCRIPT NAMES FOR \p AND \P


       Arabic,  Armenian,  Avestan, Balinese, Bamum, Batak, Bengali, Bopomofo,
       Brahmi, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian,  Chakma,
       Cham,  Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
       Devanagari,  Egyptian_Hieroglyphs,  Ethiopic,   Georgian,   Glagolitic,
       Gothic,  Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
       gana,  Imperial_Aramaic,  Inherited,  Inscriptional_Pahlavi,   Inscrip-
       tional_Parthian,   Javanese,   Kaithi,   Kannada,  Katakana,  Kayah_Li,
       Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B,  Lisu,  Lycian,
       Lydian,    Malayalam,    Mandaic,    Meetei_Mayek,    Meroitic_Cursive,
       Meroitic_Hieroglyphs,  Miao,  Mongolian,  Myanmar,  New_Tai_Lue,   Nko,
       Ogham,    Old_Italic,   Old_Persian,   Old_South_Arabian,   Old_Turkic,
       Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic,  Samari-
       tan,  Saurashtra,  Sharada,  Shavian, Sinhala, Sora_Sompeng, Sundanese,
         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

         (?|...)         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 start of a  pattern  or  after
       one of the newline-setting options with similar syntax:

         (*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)


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)

         \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)


NEWLINE CONVENTIONS


       These are recognized only at the very start of the pattern or  after  a
       (*BSR_...), (*UTF8), (*UTF16), (*UTF32) or (*UCP) option.

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


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: 11 November 2012
       Copyright (c) 1997-2012 University of Cambridge.


PCRE 8.32 11 November 2012 PCRESYNTAX(3)



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