PCRE2SYNTAX(3)             Library Functions Manual             PCRE2SYNTAX(3)

       PCRE2 - Perl-compatible regular expressions (revised API)


       The  full syntax and semantics of the regular expressions that are sup-
       ported by PCRE2 are described in the pcre2pattern  documentation.  This
       document contains a quick-reference summary of the syntax.


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


       This  table  applies to ASCII and Unicode environments. An unrecognized
       escape sequence causes an error.

         \a         alarm, that is, the BEL character (hex 07)
         \cx        "control-x", where x is any ASCII printing 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..

       If PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX is set ("ALT_BSUX mode"), the
       following are also recognized:

         \U         the character "U"
         \uhhhh     character with hex code hhhh
         \u{hh..}   character with hex code hh.. but only for EXTRA_ALT_BSUX

       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  dig-
       its  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".

       Note that \0dd is always an octal code. The treatment of backslash fol-
       lowed  by  a non-zero digit is complicated; for details see the section
       "Non-printing characters"  in  the  pcre2pattern  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).


         .          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{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

       \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.

       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 behav-
       iour of these escape sequences is changed to use Unicode properties and
       they match many more characters.


         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


         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.


       Adlam,  Ahom,  Anatolian_Hieroglyphs,  Arabic, Armenian, Avestan, Bali-
       nese, Bamum, Bassa_Vah, Batak, Bengali,  Bhaiksuki,  Bopomofo,  Brahmi,
       Braille,  Buginese, Buhid, Canadian_Aboriginal, Carian, Caucasian_Alba-
       nian, Chakma, Cham, Cherokee, Chorasmian,  Common,  Coptic,  Cuneiform,
       Cypriot,  Cypro_Minoan,  Cyrillic,  Deseret,  Devanagari,  Dives_Akuru,
       Dogra,  Duployan,  Egyptian_Hieroglyphs,  Elbasan,  Elymaic,  Ethiopic,
       Georgian,  Glagolitic, Gothic, Grantha, Greek, Gujarati, Gunjala_Gondi,
       Gurmukhi, Han, Hangul, Hanifi_Rohingya, Hanunoo, Hatran, Hebrew,  Hira-
       gana,   Imperial_Aramaic,  Inherited,  Inscriptional_Pahlavi,  Inscrip-
       tional_Parthian,  Javanese,  Kaithi,   Kannada,   Katakana,   Kayah_Li,
       Kharoshthi,  Khitan_Small_Script, Khmer, Khojki, Khudawadi, Lao, Latin,
       Lepcha, Limbu, Linear_A,  Linear_B,  Lisu,  Lycian,  Lydian,  Mahajani,
       Makasar,  Malayalam, Mandaic, Manichaean, Marchen, Masaram_Gondi, Mede-
       faidrin, Meetei_Mayek, Mende_Kikakui, Meroitic_Cursive, Meroitic_Hiero-
       glyphs, Miao, Modi, Mongolian, Mro, Multani, Myanmar, Nabataean, Nandi-
       nagari, New_Tai_Lue, Newa, Nko,  Nushu,  Nyakeng_Puachue_Hmong,  Ogham,
       Ol_Chiki,  Old_Hungarian,  Old_Italic,  Old_North_Arabian,  Old_Permic,
       Old_Persian, Old_Sogdian,  Old_South_Arabian,  Old_Turkic,  Old_Uyghur,
       Oriya,  Osage, Osmanya, Pahawh_Hmong, Palmyrene, Pau_Cin_Hau, Phags_Pa,
       Phoenician,  Psalter_Pahlavi,  Rejang,  Runic,  Samaritan,  Saurashtra,
       Sharada, Shavian, Siddham, SignWriting, Sinhala, Sogdian, Sora_Sompeng,
       Soyombo, Sundanese, Syloti_Nagri, Syriac,  Tagalog,  Tagbanwa,  Tai_Le,
       Tai_Tham, Tai_Viet, Takri, Tamil, Tangsa, Tangut, Telugu, Thaana, Thai,
       Tibetan, Tifinagh, Tirhuta,  Toto,  Ugaritic,  Vai,  Vithkuqi,  Wancho,
       Warang_Citi, Yezidi, Yi, Zanabazar_Square.


         [...]       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  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.


         ?           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


         \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


         \K          set reported start of match

       From  release 10.38 \K is not permitted by default in lookaround asser-
       tions,   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.




         (...)           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

       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.


         (?>...)         atomic non-capture group
         (*atomic:...)   atomic non-capture group


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

       Changes  of these options within a group are automatically cancelled at
       the end of the group.

         (?i)            caseless
         (?J)            allow duplicate named groups
         (?m)            multiline
         (?n)            no auto capture
         (?s)            single line (dotall)
         (?U)            default ungreedy (lazy)
         (?x)            extended: ignore white space except in classes
         (?xx)           as (?x) but also ignore space and tab in classes
         (?-...)         unset option(s)
         (?^)            unset imnsx options

       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:...).

       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.

         (*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)

       Note that LIMIT_DEPTH, LIMIT_HEAP, and LIMIT_MATCH can only reduce  the
       value   of   the   limits   set  by  the  caller  of  pcre2_match()  or
       pcre2_dfa_match(), 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.


       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
         (*NUL)          the NUL character (binary zero)


       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


         (?=...)                     )
         (*pla:...)                  ) positive lookahead
         (*positive_lookahead:...)   )

         (?!...)                     )
         (*nla:...)                  ) negative lookahead
         (*negative_lookahead:...)   )

         (?<=...)                    )
         (*plb:...)                  ) positive lookbehind
         (*positive_lookbehind:...)  )

         (?<!...)                    )
         (*nlb:...)                  ) negative lookbehind
         (*negative_lookbehind:...)  )

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


       These assertions are specific to PCRE2 and are not Perl-compatible.

         (?*...)                                )
         (*napla:...)                           ) synonyms
         (*non_atomic_positive_lookahead:...)   )

         (?<*...)                               )
         (*naplb:...)                           ) synonyms
         (*non_atomic_positive_lookbehind:...)  )


         (*script_run:...)           ) script run, can be backtracked into
         (*sr:...)                   )

         (*atomic_script_run:...)    ) atomic script run
         (*asr:...)                  )


         \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)


         (?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)



         (?(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

       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.


       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:

         (*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
         (*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

       The effect of one of these verbs in a group called as a  subroutine  is
       confined to the subroutine call.


         (?C)            callout (assumed number 0)
         (?Cn)           callout with numerical data n
         (?C"text")      callout with string data

       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.


       pcre2pattern(3),   pcre2api(3),   pcre2callout(3),    pcre2matching(3),


       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.


       Last updated: 30 August 2021
       Copyright (c) 1997-2021 University of Cambridge.

PCRE2 10.38                     30 August 2021                  PCRE2SYNTAX(3)
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