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PCRE2SYNTAX(3)		   Library Functions Manual		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  de-
       tails  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.

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 char-
       acter set at release 5.18.

SCRIPT NAMES FOR \p AND	\P

       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,	 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,  Hiragana,  Imperial_Aramaic,
       Inherited,   Inscriptional_Pahlavi,  Inscriptional_Parthian,  Javanese,
       Kaithi, Kannada,	Katakana, Kayah_Li,  Kharoshthi,  Khitan_Small_Script,
       Khmer,  Khojki,	Khudawadi,  Lao,  Latin, Lepcha, Limbu,	Linear_A, Lin-
       ear_B, Lisu, Lycian, Lydian,  Mahajani,	Makasar,  Malayalam,  Mandaic,
       Manichaean,    Marchen,	 Masaram_Gondi,	  Medefaidrin,	 Meetei_Mayek,
       Mende_Kikakui, Meroitic_Cursive,	Meroitic_Hieroglyphs, Miao, Modi, Mon-
       golian,	Mro,  Multani,	Myanmar,  Nabataean, Nandinagari, New_Tai_Lue,
       Newa, Nko, Nushu, Nyakeng_Puachue_Hmong,	Ogham,	Ol_Chiki,  Old_Hungar-
       ian,  Old_Italic,  Old_North_Arabian, Old_Permic, Old_Persian, Old_Sog-
       dian,  Old_South_Arabian,  Old_Turkic,  Oriya,  Osage,	Osmanya,   Pa-
       hawh_Hmong,     Palmyrene,     Pau_Cin_Hau,    Phags_Pa,	   Phoenician,
       Psalter_Pahlavi,	Rejang,	Runic, Samaritan,  Saurashtra,	Sharada,  Sha-
       vian,  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, Tifi-
       nagh, Tirhuta, Ugaritic,	Vai, Wancho,  Warang_Citi,  Yezidi,  Yi,  Zan-
       abazar_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

	 (...)		 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 af-
       ter 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 op-
       tion 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 op-
       tion 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
       University Computing Service
       Cambridge, England.

REVISION

       Last updated: 28	December 2019
       Copyright (c) 1997-2019 University of Cambridge.

PCRE2 10.35		       28 December 2019			PCRE2SYNTAX(3)

NAME | PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY | QUOTING | ESCAPED CHARACTERS | CHARACTER TYPES | GENERAL CATEGORY PROPERTIES FOR \p and \P | PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P | SCRIPT NAMES FOR \p AND \P | CHARACTER CLASSES | QUANTIFIERS | ANCHORS AND SIMPLE ASSERTIONS | REPORTED MATCH POINT SETTING | ALTERNATION | CAPTURING | ATOMIC GROUPS | COMMENT | OPTION SETTING | NEWLINE CONVENTION | WHAT \R MATCHES | LOOKAHEAD AND LOOKBEHIND ASSERTIONS | NON-ATOMIC LOOKAROUND ASSERTIONS | SCRIPT RUNS | BACKREFERENCES | SUBROUTINE REFERENCES (POSSIBLY RECURSIVE) | CONDITIONAL PATTERNS | BACKTRACKING CONTROL | CALLOUTS | SEE ALSO | AUTHOR | REVISION

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