PCRESYNTAX(3)

NAME

PCRE - Perl-compatible regular expressions

PCRE REGULAR EXPRESSION SYNTAX SUMMARY

The full syntax and semantics of the regular expressions that are supported by PCRE are described in the pcrepattern documentation. This document contains just 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

CHARACTERS

\a alarm, that is, the BEL character (hex 07)

\cx "control-x", where x is any character

\e escape (hex 1B)

\f formfeed (hex 0C)

\n newline (hex 0A)

\r carriage return (hex 0D)

\t tab (hex 09)

\ddd character with octal code ddd, or backreference

\xhh character with hex code hh

\x{hhh..} character with hex code hhh..

CHARACTER TYPES

. any character except newline;: in dotall mode, any character whatsoever
\C one byte, even in UTF-8 mode (best avoided) \d a decimal digit \D a character that is not a decimal digit \h a horizontal whitespace character \H a character that is not a horizontal whitespace character \p{xx} a character with the xx property \P{xx} a character without the xx property \R a newline sequence \s a whitespace character \S a character that is not a whitespace character \v a vertical whitespace character \V a character that is not a vertical whitespace character \w a "word" character \W a "non-word" character \X an extended Unicode sequence
In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.

GENERAL CATEGORY PROPERTY CODES 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

SCRIPT NAMES FOR \p AND \P

Arabic, Armenian, Avestan, Balinese, Bamum, Bengali, Bopomofo, Braille, Buginese, Buhid, Canadian_Aboriginal, Carian, Cham, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Egyptian_Hieroglyphs, Ethiopic, Georgian, Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Imperial_Aramaic, Inherited, Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kannada, Katakana, Kayah_Li, Kharoshthi, Khmer, Lao, Latin, Lepcha, Limbu, Linear_B, Lisu, Lycian, Lydian, Malayalam, Meetei_Mayek, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian, Old_South_Arabian, Old_Turkic, Ol_Chiki, Oriya, Osmanya, Phags_Pa, Phoenician, Rejang, Runic, Samaritan, Saurashtra, Shavian, Sinhala, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tai_Tham, Tai_Viet, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Vai, Yi.

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 whitespace

upper upper case letter

word same as \w

xdigit hexadecimal digit

In PCRE, POSIX character set names recognize only ASCII characters. 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 (only ASCII letters recognized) \B not a word boundary ^ start of subject: also after internal newline in multiline mode
\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

MATCH POINT RESET

\K reset start of match

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

(?i) caseless

(?J) allow duplicate names

(?m) multiline

(?s) single line (dotall)

(?U) default ungreedy (lazy)

(?x) extended (ignore white space)

(?-...) unset option(s)

The following is recognized only at the start of a pattern or after one of the newline-setting options with similar syntax:

(*UTF8) set UTF-8 mode

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

\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 (PCRE extension)

\g'+n' call subpattern by relative number (PCRE extension)

\g<-n> call subpattern by relative number (PCRE extension)

\g'-n' call subpattern by relative number (PCRE 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 (PCRE)

(?(R)... overall recursion condition

(?(Rn)... specific group recursion condition

(?(R&name)... specific recursion condition

(?(DEFINE)... define subpattern for reference

(?(assert)... assertion condition

BACKTRACKING CONTROL

The following act immediately they are reached:

(*ACCEPT) force successful match

(*FAIL) force backtrack; synonym (*F)

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 start to current matching position

(*THEN) local failure, backtrack to next alternation

NEWLINE CONVENTIONS

These are recognized only at the very start of the pattern or after a (*BSR_...) or (*UTF8) option.

(*CR) carriage return only

(*LF) linefeed only

(*CRLF) carriage return followed by linefeed

(*ANYCRLF) all three of the above

(*ANY) any Unicode newline sequence

WHAT \R MATCHES

These are recognized only at the very start of the pattern or after a (*...) option that sets the newline convention or UTF-8 mode.: (*BSR_ANYCRLF) CR, LF, or CRLF
(*BSR_UNICODE) any Unicode newline sequence

CALLOUTS

(?C) callout

(?Cn) callout with data n

AUTHOR

Philip Hazel

University Computing Service

Cambridge CB2 3QH, England.

docs.sk

comprehensive documentation repository

See also