# RE2 regular expression syntax reference

This page lists the regular expression syntax accepted by RE2.
It also lists syntax accepted by PCRE, PERL, and VIM.
Grayed out expressions are not supported by RE2.
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*`) VIM
`x{-}` | (≡ `x*?`) VIM
`x{-n}` | (≡ `x{n}?`) VIM
`x=` | (≡ `x?`) 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
`x++` | one or more `x`, possessive
`x?+` | zero or one `x`, possessive
`x{n,m}+` | `n` or ... or `m` `x`, possessive
`x{n,}+` | `n` or more `x`, possessive
`x{n}+` | exactly `n` `x`, possessive
Grouping:
`(re)` | numbered capturing group (submatch)
`(?P<name>re)` | named & numbered capturing group (submatch)
`(?<name>re)` | named & numbered capturing group (submatch)
`(?'name're)` | named & numbered capturing group (submatch)
`(?:re)` | non-capturing group
`(?flags)` | set flags within current group; non-capturing
`(?flags:re)` | set flags during re; non-capturing
`(?#text)` | comment
`(?|x|y|z)` | branch numbering reset
`(?>re)` | possessive match of `re`
`re@>` | possessive match of `re` VIM
`%(re)` | non-capturing group 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 PCRE
`\G` | at end of last match PERL
`\Z` | at end of text, or before newline at end of text
`\z` | at end of text
`(?=re)` | before text matching `re`
`(?!re)` | before text not matching `re`
`(?<=re)` | after text matching `re`
`(?<!re)` | after text not matching `re`
`re&` | before text matching `re` VIM
`re@=` | before text matching `re` VIM
`re@!` | before text not matching `re` VIM
`re@<=` | after text matching `re` VIM
`re@<!` | after text not matching `re` VIM
`\zs` | sets start of match (= \K) VIM
`\ze` | sets end of match VIM
`\%^` | beginning of file VIM
`\%$` | end of file VIM
`\%V` | on screen VIM
`\%#` | cursor position VIM
`\%'m` | mark `m` position VIM
`\%23l` | in line 23 VIM
`\%23c` | in column 23 VIM
`\%23v` | in virtual column 23 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
`\b` | backspace (use `\010`)
`\cK` | control char ^K (use `\001` etc)
`\e` | escape (use `\033`)
`\g1` | backreference
`\g{1}` | backreference
`\g{+1}` | backreference
`\g{-1}` | backreference
`\g{name}` | named backreference
`\g<name>` | subroutine call
`\g'name'` | subroutine call
`\k<name>` | named backreference
`\k'name'` | named backreference
`\lX` | lowercase `X`
`\ux` | uppercase `x`
`\L...\E` | lowercase text `...`
`\K` | reset beginning of `$0`
`\N{name}` | named Unicode character
`\R` | line break
`\U...\E` | upper case text `...`
`\X` | extended Unicode sequence
`\%d123` | decimal character 123 VIM
`\%xFF` | hex character FF VIM
`\%o123` | octal character 123 VIM
`\%u1234` | Unicode character 0x1234 VIM
`\%U12345678` | Unicode character 0x12345678 VIM
Character class elements:
`x` | single character
`A-Z` | character range (inclusive)
`\d` | Perl character class
`[:foo:]` | ASCII character class `foo`
`\p{Foo}` | Unicode character class `Foo`
`\pF` | Unicode character class `F` (one-letter name)
Named character classes as character class elements:
`[\d]` | digits (≡ `\d`)
`[^\d]` | not digits (≡ `\D`)
`[\D]` | not digits (≡ `\D`)
`[^\D]` | not not digits (≡ `\d`)
`[[:name:]]` | named ASCII class inside character class (≡ `[:name:]`)
`[^[:name:]]` | named ASCII class inside negated character class (≡ `[:^name:]`)
`[\p{Name}]` | named Unicode property inside character class (≡ `\p{Name}`)
`[^\p{Name}]` | named Unicode property inside negated character class (≡ `\P{Name}`)
Perl character classes (all ASCII-only):
`\d` | digits (≡ `[0-9]`)
`\D` | not digits (≡ `[^0-9]`)
`\s` | whitespace (≡ `[\t\n\f\r ]`)
`\S` | not whitespace (≡ `[^\t\n\f\r ]`)
`\w` | word characters (≡ `[0-9A-Za-z_]`)
`\W` | not word characters (≡ `[^0-9A-Za-z_]`)
`\h` | horizontal space
`\H` | not horizontal space
`\v` | vertical space
`\V` | not vertical space
ASCII character classes:
`[[:alnum:]]` | alphanumeric (≡ `[0-9A-Za-z]`)
`[[:alpha:]]` | alphabetic (≡ `[A-Za-z]`)
`[[:ascii:]]` | ASCII (≡ `[\x00-\x7F]`)
`[[:blank:]]` | blank (≡ `[\t ]`)
`[[:cntrl:]]` | control (≡ `[\x00-\x1F\x7F]`)
`[[:digit:]]` | digits (≡ `[0-9]`)
`[[:graph:]]` | graphical (≡ `[!-~] == [A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~]`)
`[[: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
`Co` | private use
`Cs` | surrogate
`L` | letter
`LC` | cased letter
`L&` | cased letter
`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
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
Hiragana
Imperial_Aramaic
Inherited
Inscriptional_Pahlavi
Inscriptional_Parthian
Javanese
Kaithi
Kannada
Katakana
Kawi
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
Medefaidrin
Meetei_Mayek
Mende_Kikakui
Meroitic_Cursive
Meroitic_Hieroglyphs
Miao
Modi
Mongolian
Mro
Multani
Myanmar
Nabataean
Nag_Mundari
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
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
Vim character classes:
`\i` | identifier character VIM
`\I` | `\i` except digits VIM
`\k` | keyword character VIM
`\K` | `\k` except digits VIM
`\f` | file name character VIM
`\F` | `\f` except digits VIM
`\p` | printable character VIM
`\P` | `\p` except digits VIM
`\s` | whitespace character (≡ `[ \t]`) VIM
`\S` | non-white space character (≡ `[^ \t]`) VIM
`\d` | digits (≡ `[0-9]`) VIM
`\D` | not `\d` VIM
`\x` | hex digits (≡ `[0-9A-Fa-f]`) VIM
`\X` | not `\x` VIM
`\o` | octal digits (≡ `[0-7]`) VIM
`\O` | not `\o` VIM
`\w` | word character VIM
`\W` | not `\w` VIM
`\h` | head of word character VIM
`\H` | not `\h` VIM
`\a` | alphabetic VIM
`\A` | not `\a` VIM
`\l` | lowercase VIM
`\L` | not lowercase VIM
`\u` | uppercase VIM
`\U` | not uppercase VIM
`\_x` | `\x` plus newline, for any `x` VIM
Vim flags:
`\c` | ignore case VIM
`\C` | match case VIM
`\m` | magic VIM
`\M` | nomagic VIM
`\v` | verymagic VIM
`\V` | verynomagic VIM
`\Z` | ignore differences in Unicode combining characters VIM
Magic:
`(?{code})` | arbitrary Perl code PERL
`(??{code})` | postponed arbitrary Perl code PERL
`(?n)` | recursive call to regexp capturing group `n`
`(?+n)` | recursive call to relative group `+n`
`(?-n)` | recursive call to relative group `-n`
`(?C)` | PCRE callout PCRE
`(?R)` | recursive call to entire regexp (≡ `(?0)`)
`(?&name)` | recursive call to named group
`(?P=name)` | named backreference
`(?P>name)` | recursive call to named group
`(?(cond)true|false)` | conditional branch
`(?(cond)true)` | conditional branch
`(*ACCEPT)` | make regexps more like Prolog
`(*COMMIT)` |
`(*F)` |
`(*FAIL)` |
`(*MARK)` |
`(*PRUNE)` |
`(*SKIP)` |
`(*THEN)` |
`(*ANY)` | set newline convention
`(*ANYCRLF)` |
`(*CR)` |
`(*CRLF)` |
`(*LF)` |
`(*BSR_ANYCRLF)` | set \R convention PCRE
`(*BSR_UNICODE)` | PCRE