RE2 regular expression syntax reference
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Single characters:
.	any character, possibly including newline (s=true)
[xyz]	character class
[^xyz]	negated character class
\d	Perl character class
\D	negated Perl character class
[[:alpha:]]	ASCII character class
[[:^alpha:]]	negated ASCII character class
\pN	Unicode character class (one-letter name)
\p{Greek}	Unicode character class
\PN	negated Unicode character class (one-letter name)
\P{Greek}	negated Unicode character class

Composites:
xy	«x» followed by «y»
x|y	«x» or «y» (prefer «x»)

Repetitions:
x*	zero or more «x», prefer more
x+	one or more «x», prefer more
x?	zero or one «x», prefer one
x{n,m}	«n» or «n»+1 or ... or «m» «x», prefer more
x{n,}	«n» or more «x», prefer more
x{n}	exactly «n» «x»
x*?	zero or more «x», prefer fewer
x+?	one or more «x», prefer fewer
x??	zero or one «x», prefer zero
x{n,m}?	«n» or «n»+1 or ... or «m» «x», prefer fewer
x{n,}?	«n» or more «x», prefer fewer
x{n}?	exactly «n» «x»
x{}	(== x*) NOT SUPPORTED vim
x{-}	(== x*?) NOT SUPPORTED vim
x{-n}	(== x{n}?) NOT SUPPORTED vim
x=	(== x?) NOT SUPPORTED vim

Implementation restriction: The counting forms «x{n,m}», «x{n,}», and «x{n}»
reject forms that create a minimum or maximum repetition count above 1000.
Unlimited repetitions are not subject to this restriction.

Possessive repetitions:
x*+	zero or more «x», possessive NOT SUPPORTED
x++	one or more «x», possessive NOT SUPPORTED
x?+	zero or one «x», possessive NOT SUPPORTED
x{n,m}+	«n» or ... or «m» «x», possessive NOT SUPPORTED
x{n,}+	«n» or more «x», possessive NOT SUPPORTED
x{n}+	exactly «n» «x», possessive NOT SUPPORTED

Grouping:
(re)	numbered capturing group (submatch)
(?P<name>re)	named & numbered capturing group (submatch)
(?<name>re)	named & numbered capturing group (submatch) NOT SUPPORTED
(?'name're)	named & numbered capturing group (submatch) NOT SUPPORTED
(?:re)	non-capturing group
(?flags)	set flags within current group; non-capturing
(?flags:re)	set flags during re; non-capturing
(?#text)	comment NOT SUPPORTED
(?|x|y|z)	branch numbering reset NOT SUPPORTED
(?>re)	possessive match of «re» NOT SUPPORTED
re@>	possessive match of «re» NOT SUPPORTED vim
%(re)	non-capturing group NOT SUPPORTED vim

Flags:
i	case-insensitive (default false)
m	multi-line mode: «^» and «$» match begin/end line in addition to begin/end text (default false)
s	let «.» match «\n» (default false)
U	ungreedy: swap meaning of «x*» and «x*?», «x+» and «x+?», etc (default false)
Flag syntax is «xyz» (set) or «-xyz» (clear) or «xy-z» (set «xy», clear «z»).

Empty strings:
^	at beginning of text or line («m»=true)
$	at end of text (like «\z» not «\Z») or line («m»=true)
\A	at beginning of text
\b	at ASCII word boundary («\w» on one side and «\W», «\A», or «\z» on the other)
\B	not at ASCII word boundary
\G	at beginning of subtext being searched NOT SUPPORTED pcre
\G	at end of last match NOT SUPPORTED perl
\Z	at end of text, or before newline at end of text NOT SUPPORTED
\z	at end of text
(?=re)	before text matching «re» NOT SUPPORTED
(?!re)	before text not matching «re» NOT SUPPORTED
(?<=re)	after text matching «re» NOT SUPPORTED
(?<!re)	after text not matching «re» NOT SUPPORTED
re&	before text matching «re» NOT SUPPORTED vim
re@=	before text matching «re» NOT SUPPORTED vim
re@!	before text not matching «re» NOT SUPPORTED vim
re@<=	after text matching «re» NOT SUPPORTED vim
re@<!	after text not matching «re» NOT SUPPORTED vim
\zs	sets start of match (= \K) NOT SUPPORTED vim
\ze	sets end of match NOT SUPPORTED vim
\%^	beginning of file NOT SUPPORTED vim
\%$	end of file NOT SUPPORTED vim
\%V	on screen NOT SUPPORTED vim
\%#	cursor position NOT SUPPORTED vim
\%'m	mark «m» position NOT SUPPORTED vim
\%23l	in line 23 NOT SUPPORTED vim
\%23c	in column 23 NOT SUPPORTED vim
\%23v	in virtual column 23 NOT SUPPORTED vim

Escape sequences:
\a	bell (== \007)
\f	form feed (== \014)
\t	horizontal tab (== \011)
\n	newline (== \012)
\r	carriage return (== \015)
\v	vertical tab character (== \013)
\*	literal «*», for any punctuation character «*»
\123	octal character code (up to three digits)
\x7F	hex character code (exactly two digits)
\x{10FFFF}	hex character code
\C	match a single byte even in UTF-8 mode
\Q...\E	literal text «...» even if «...» has punctuation

\1	backreference NOT SUPPORTED
\b	backspace NOT SUPPORTED (use «\010»)
\cK	control char ^K NOT SUPPORTED (use «\001» etc)
\e	escape NOT SUPPORTED (use «\033»)
\g1	backreference NOT SUPPORTED
\g{1}	backreference NOT SUPPORTED
\g{+1}	backreference NOT SUPPORTED
\g{-1}	backreference NOT SUPPORTED
\g{name}	named backreference NOT SUPPORTED
\g<name>	subroutine call NOT SUPPORTED
\g'name'	subroutine call NOT SUPPORTED
\k<name>	named backreference NOT SUPPORTED
\k'name'	named backreference NOT SUPPORTED
\lX	lowercase «X» NOT SUPPORTED
\ux	uppercase «x» NOT SUPPORTED
\L...\E	lowercase text «...» NOT SUPPORTED
\K	reset beginning of «$0» NOT SUPPORTED
\N{name}	named Unicode character NOT SUPPORTED
\R	line break NOT SUPPORTED
\U...\E	upper case text «...» NOT SUPPORTED
\X	extended Unicode sequence NOT SUPPORTED

\%d123	decimal character 123 NOT SUPPORTED vim
\%xFF	hex character FF NOT SUPPORTED vim
\%o123	octal character 123 NOT SUPPORTED vim
\%u1234	Unicode character 0x1234 NOT SUPPORTED vim
\%U12345678	Unicode character 0x12345678 NOT SUPPORTED vim

Character class elements:
x	single character
A-Z	character range (inclusive)
\d	Perl character class
[:foo:]	ASCII character class «foo»
\p{Foo}	Unicode character class «Foo»
\pF	Unicode character class «F» (one-letter name)

Named character classes as character class elements:
[\d]	digits (== \d)
[^\d]	not digits (== \D)
[\D]	not digits (== \D)
[^\D]	not not digits (== \d)
[[:name:]]	named ASCII class inside character class (== [:name:])
[^[:name:]]	named ASCII class inside negated character class (== [:^name:])
[\p{Name}]	named Unicode property inside character class (== \p{Name})
[^\p{Name}]	named Unicode property inside negated character class (== \P{Name})

Perl character classes (all ASCII-only):
\d	digits (== [0-9])
\D	not digits (== [^0-9])
\s	whitespace (== [\t\n\f\r ])
\S	not whitespace (== [^\t\n\f\r ])
\w	word characters (== [0-9A-Za-z_])
\W	not word characters (== [^0-9A-Za-z_])

\h	horizontal space NOT SUPPORTED
\H	not horizontal space NOT SUPPORTED
\v	vertical space NOT SUPPORTED
\V	not vertical space NOT SUPPORTED

ASCII character classes:
[[:alnum:]]	alphanumeric (== [0-9A-Za-z])
[[:alpha:]]	alphabetic (== [A-Za-z])
[[:ascii:]]	ASCII (== [\x00-\x7F])
[[:blank:]]	blank (== [\t ])
[[:cntrl:]]	control (== [\x00-\x1F\x7F])
[[:digit:]]	digits (== [0-9])
[[:graph:]]	graphical (== [!-~] == [A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~])
[[:lower:]]	lower case (== [a-z])
[[:print:]]	printable (== [ -~] == [ [:graph:]])
[[:punct:]]	punctuation (== [!-/:-@[-`{-~])
[[:space:]]	whitespace (== [\t\n\v\f\r ])
[[:upper:]]	upper case (== [A-Z])
[[:word:]]	word characters (== [0-9A-Za-z_])
[[:xdigit:]]	hex digit (== [0-9A-Fa-f])

Unicode character class names--general category:
C	other
Cc	control
Cf	format
Cn	unassigned code points NOT SUPPORTED
Co	private use
Cs	surrogate
L	letter
LC	cased letter NOT SUPPORTED
L&	cased letter NOT SUPPORTED
Ll	lowercase letter
Lm	modifier letter
Lo	other letter
Lt	titlecase letter
Lu	uppercase letter
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	math symbol
So	other symbol
Z	separator
Zl	line separator
Zp	paragraph separator
Zs	space separator

Unicode character class names--scripts:
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
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
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
Nandinagari
New_Tai_Lue
Newa
Nko
Nushu
Nyiakeng_Puachue_Hmong
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
Wancho
Warang_Citi
Yi
Zanabazar_Square

Vim character classes:
\i	identifier character NOT SUPPORTED vim
\I	«\i» except digits NOT SUPPORTED vim
\k	keyword character NOT SUPPORTED vim
\K	«\k» except digits NOT SUPPORTED vim
\f	file name character NOT SUPPORTED vim
\F	«\f» except digits NOT SUPPORTED vim
\p	printable character NOT SUPPORTED vim
\P	«\p» except digits NOT SUPPORTED vim
\s	whitespace character (== [ \t]) NOT SUPPORTED vim
\S	non-white space character (== [^ \t]) NOT SUPPORTED vim
\d	digits (== [0-9]) vim
\D	not «\d» vim
\x	hex digits (== [0-9A-Fa-f]) NOT SUPPORTED vim
\X	not «\x» NOT SUPPORTED vim
\o	octal digits (== [0-7]) NOT SUPPORTED vim
\O	not «\o» NOT SUPPORTED vim
\w	word character vim
\W	not «\w» vim
\h	head of word character NOT SUPPORTED vim
\H	not «\h» NOT SUPPORTED vim
\a	alphabetic NOT SUPPORTED vim
\A	not «\a» NOT SUPPORTED vim
\l	lowercase NOT SUPPORTED vim
\L	not lowercase NOT SUPPORTED vim
\u	uppercase NOT SUPPORTED vim
\U	not uppercase NOT SUPPORTED vim
\_x	«\x» plus newline, for any «x» NOT SUPPORTED vim

Vim flags:
\c	ignore case NOT SUPPORTED vim
\C	match case NOT SUPPORTED vim
\m	magic NOT SUPPORTED vim
\M	nomagic NOT SUPPORTED vim
\v	verymagic NOT SUPPORTED vim
\V	verynomagic NOT SUPPORTED vim
\Z	ignore differences in Unicode combining characters NOT SUPPORTED vim

Magic:
(?{code})	arbitrary Perl code NOT SUPPORTED perl
(??{code})	postponed arbitrary Perl code NOT SUPPORTED perl
(?n)	recursive call to regexp capturing group «n» NOT SUPPORTED
(?+n)	recursive call to relative group «+n» NOT SUPPORTED
(?-n)	recursive call to relative group «-n» NOT SUPPORTED
(?C)	PCRE callout NOT SUPPORTED pcre
(?R)	recursive call to entire regexp (== (?0)) NOT SUPPORTED
(?&name)	recursive call to named group NOT SUPPORTED
(?P=name)	named backreference NOT SUPPORTED
(?P>name)	recursive call to named group NOT SUPPORTED
(?(cond)true|false)	conditional branch NOT SUPPORTED
(?(cond)true)	conditional branch NOT SUPPORTED
(*ACCEPT)	make regexps more like Prolog NOT SUPPORTED
(*COMMIT)	NOT SUPPORTED
(*F)	NOT SUPPORTED
(*FAIL)	NOT SUPPORTED
(*MARK)	NOT SUPPORTED
(*PRUNE)	NOT SUPPORTED
(*SKIP)	NOT SUPPORTED
(*THEN)	NOT SUPPORTED
(*ANY)	set newline convention NOT SUPPORTED
(*ANYCRLF)	NOT SUPPORTED
(*CR)	NOT SUPPORTED
(*CRLF)	NOT SUPPORTED
(*LF)	NOT SUPPORTED
(*BSR_ANYCRLF)	set \R convention NOT SUPPORTED pcre
(*BSR_UNICODE)	NOT SUPPORTED pcre