Provided by: libpcre2-dev_10.32-5_amd64 bug

NAME

       PCRE2 - Perl-compatible regular expressions (revised API)

PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY


       The  full  syntax and semantics of the regular expressions that are supported 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.

         \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..
         \U         "U" if PCRE2_ALT_BSUX is set (otherwise is an error)
         \N{U+hh..} character with Unicode code point hh.. (Unicode mode only)
         \uhhhh     character with hex code hhhh (if PCRE2_ALT_BSUX is set)
         \xhh       character with hex code hh
         \x{hh..}   character with hex code hh..

       Note  that \0dd is always an octal code. The treatment of backslash followed 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).

       When \x is not followed by {, from zero  to  two  hexadecimal  digits  are  read,  but  if
       PCRE2_ALT_BSUX is set, \x must be followed by two hexadecimal digits 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, it matches a literal "u".

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 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

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 character set at release
       5.18.

SCRIPT NAMES FOR \p AND \P


       Adlam, Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Balinese, Bamum, Bassa_Vah,
       Batak,   Bengali,    Bhaiksuki,    Bopomofo,    Brahmi,    Braille,    Buginese,    Buhid,
       Canadian_Aboriginal,  Carian,  Caucasian_Albanian, Chakma, Cham, Cherokee, Common, Coptic,
       Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Dogra, Duployan,  Egyptian_Hieroglyphs,
       Elbasan,  Ethiopic, Georgian, Glagolitic, Gothic, Grantha, Greek, Gujarati, Gunjala_Gondi,
       Gurmukhi,   Han,   Hangul,   Hanifi_Rohingya,   Hanunoo,   Hatran,    Hebrew,    Hiragana,
       Imperial_Aramaic,   Inherited,  Inscriptional_Pahlavi,  Inscriptional_Parthian,  Javanese,
       Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer,  Khojki,  Khudawadi,  Lao,  Latin,
       Lepcha,  Limbu,  Linear_A,  Linear_B,  Lisu, Lycian, Lydian, Mahajani, Makasar, Malayalam,
       Mandaic, Manichaean, Marchen,  Masaram_Gondi,  Medefaidrin,  Meetei_Mayek,  Mende_Kikakui,
       Meroitic_Cursive,  Meroitic_Hieroglyphs,  Miao,  Modi,  Mongolian,  Mro, Multani, Myanmar,
       Nabataean, New_Tai_Lue, Newa, Nko,  Nushu,  Ogham,  Ol_Chiki,  Old_Hungarian,  Old_Italic,
       Old_North_Arabian,  Old_Permic,  Old_Persian,  Old_Sogdian, Old_South_Arabian, Old_Turkic,
       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, Tangut, Telugu, Thaana, Thai,
       Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi, Yi, Zanabazar_Square.

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

       \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

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

         (?i)            caseless
         (?J)            allow duplicate names
         (?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-capturing 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


         (?=...)         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 (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 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 (PCRE2 extension)
         \g'+n'          call subpattern by relative number (PCRE2 extension)
         \g<-n>          call subpattern by relative number (PCRE2 extension)
         \g'-n'          call subpattern 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 subpattern 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 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
         (*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
       University Computing Service
       Cambridge, England.

REVISION


       Last updated: 02 September 2018
       Copyright (c) 1997-2018 University of Cambridge.