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NAME

       PCRE - Perl-compatible regular expressions

PCRE REGULAR EXPRESSION SYNTAX SUMMARY


       The  full  syntax  and  semantics  of  the regular expressions that are
       supported 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
                  escape (hex 1B)
                  form feed (hex 0C)
         
         newline (hex 0A)
         
         carriage return (hex 0D)
         	         tab (hex 09)
         dd       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  dd  is  always  an octal code, and that \8 and \9 are the
       literal 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
                  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-
       specific 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
       properties 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
       character set at release 5.18 and PCRE changed at release 8.34.

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,
       Hiragana,     Imperial_Aramaic,    Inherited,    Inscriptional_Pahlavi,
       Inscriptional_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,
       Samaritan,  Saurashtra,  Sharada,   Shavian,   Sinhala,   Sora_Sompeng,
       Sundanese,  Syloti_Nagri,  Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham,
       Tai_Viet,  Takri,  Tamil,  Telugu,  Thaana,  Thai,  Tibetan,  Tifinagh,
       Ugaritic, Vai, 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


         
              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
       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.

         (*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.



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