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pcre2syntax(3)                                                  pcre2syntax(3)




NAME

       PCRE2 - Perl-compatible regular expressions (revised API)


PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY


       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.


QUOTING


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


ESCAPED CHARACTERS


       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).


CHARACTER TYPES


         .          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.

       Property descriptions in \p and \P  are  matched  caselessly;  hyphens,
       underscores,  and white space are ignored, in accordance with Unicode's
       "loose matching" rules.


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
         Lc         Ll, Lu, or Lt
         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


PCRE2 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.


BINARY PROPERTIES FOR \p AND \P


       Unicode  defines  a  number  of  binary properties, that is, properties
       whose only values are true or false. You can obtain  a  list  of  those
       that  are  recognized  by \p and \P, along with their abbreviations, by
       running this command:

         pcre2test -LP


SCRIPT MATCHING WITH \p AND \P


       Many script names and their 4-letter abbreviations  are  recognized  in
       \p{sc:...}  or  \p{scx:...} items, or on their own with \p (and also \P
       of course). You can obtain a list of these scripts by running this com-
       mand:

         pcre2test -LS


THE BIDI_CLASS PROPERTY FOR \p AND \P


         \p{Bidi_Class:<class>}   matches a character with the given class
         \p{BC:<class>}           matches a character with the given class

       The recognized classes are:

         AL          Arabic letter
         AN          Arabic number
         B           paragraph separator
         BN          boundary neutral
         CS          common separator
         EN          European number
         ES          European separator
         ET          European terminator
         FSI         first strong isolate
         L           left-to-right
         LRE         left-to-right embedding
         LRI         left-to-right isolate
         LRO         left-to-right override
         NSM         non-spacing mark
         ON          other neutral
         PDF         pop directional format
         PDI         pop directional isolate
         R           right-to-left
         RLE         right-to-left embedding
         RLI         right-to-left isolate
         RLO         right-to-left override
         S           segment separator
         WS          which space


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  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.


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 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


REPORTED MATCH POINT SETTING


         \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.


ALTERNATION


         expr|expr|expr...


CAPTURING


         (...)           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 GROUPS


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


COMMENT


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


OPTION SETTING

       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.


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
         (*NUL)          the NUL character (binary zero)


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


         (?=...)                     )
         (*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.


NON-ATOMIC LOOKAROUND ASSERTIONS


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

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

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


SCRIPT RUNS


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

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


BACKREFERENCES


         \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)


SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)


         (?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)


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 (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.


BACKTRACKING CONTROL


       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.


CALLOUTS


         (?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.


SEE ALSO


       pcre2pattern(3),    pcre2api(3),   pcre2callout(3),   pcre2matching(3),
       pcre2(3).


AUTHOR


       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.


REVISION


       Last updated: 12 January 2022
       Copyright (c) 1997-2022 University of Cambridge.



PCRE2 10.40                     12 January 2022                 pcre2syntax(3)

pcre2 10.40 - Generated Mon May 9 19:30:28 CDT 2022
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