Regular Expression Cheat Sheet - PCRE
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README.md

README.md

Regular Expression Cheat Sheet - PCRE

Anchor Description Example Valid match Invalid
^ start of string or line ^foam foam bath foam
\A start of string in any match mode \Afoam foam bath foam
$ end of string or line finish$ finish finnish
\Z end of string, or char before last new line in any match mode finish\Z finish finnish
\z end of string, in any match mode.
\G end of the previous match or the start of the string for the first match ^(get|set)|\G\w+$ setValue seValue
\b word boundary; position between a word character (\w), and a nonword character (\W) \bis\b This island is beautiful This island isn't beautiful
\B not-word-boundary. \Bland island peninsula
Assertion Description Example Valid match Invalid
(?=...) positive lookahead question(?=s) questions question
(?!...) negative lookahead answer(?!s) answer answers
(?<=...) positive look-behind (?<=appl)e apple application
(?<!...) negative look-behind (?<!goo)d mood good
Char class Description Example Valid match Invalid
[ ] class definition [axf] a, x, f b
[ - ] class definition range [a-c] a, b, c d
[ \ ] escape inside class [a-f.] a, b, . g
[^ ] Not in class [^abc] d, e a
[:class:] POSIX class [:alpha:] string 0101
. match any chars except new line b.ttle battle, bottle bttle
\s white space, [\n\r\f\t ] good\smorning good morning good.morning
\S no-white space, [^\n\r\f\t] good\Smorning goodmorning good morning
\d digit \d{2} 23 1a
\D non-digit \D{3} foo, bar fo1
\w word, [a-z-A-Z0-9_] \w{4} v411 v4.1
\W non word, [^a-z-A-Z0-9_] .$%? .$%? .ab?
Special character Description
|general escape
\n new line
\r carriage return
\t tab
\v vertical tab
\f form feed
\a alarm
[\b] backspace
\e escape
\cchar Ctrl + char(ie:\cc is Ctrl+c)
\ooo three digit octal (ie: \123)
\xhh one or two digit hexadecimal (ie: \x10)
\x{hex} any hexadecimal code (ie: \x{1234})
\p{xx} char with unicode property (ie: \p{Arabic}
\P{xx} char without unicode property
Sequence Description Example Valid match Invalid
| alternation apple|orange apple, orange melon
( ) subpattern foot(er|ball) footer or footbal footpath
(?P<name>...) subpattern, and capture submatch into name (?P<greeting>hello) hello hallo
(?:...) subpattern, but does not capture submatch (?:hello) hello hallo
+ one or more quantifier ye+ah yeah, yeeeah yah
* zero or more quantifier ye*ah yeeah, yeeeah, yah yeh
? zero or one quantifier yes? yes, ye yess
?? zero or one, as few times as possible (lazy) yea??h yeah yeaah
+? one or more lazy /<.+?>/g <P>foo</P> matches only <P> and </P>
*? zero or more, lazy /<.*?>/g <html>
{n} n times exactly fo{2} foo fooo
{n,m} from n to m times go{2,3}d good,goood gooood
{n,} at least n times go{2,} goo, gooo go
(?(condition)...) if-then pattern (<)?[p](?(1)>) <p>, p <p
(?(condition)...|...) if-then-else pattern `^(?(?=q)que ans)` question, answer
Pattern modifier Description
g global match
i case-insensitiv, match both uppercase and lowercase
m multiple lines
s single line (by default)
x ingore whitespace allows comments
A anchored, the pattern is forced to ^
D dollar end only, a dollar metacharacter matches only at the end
S extra analysis performed, useful for non-anchored patterns
U ungreedy, greedy patterns becomes lazy by default
X additional functionality of PCRE (PCRE extra)
J allow duplicate names for subpatterns
u unicode, pattern and subject strings are treated as UTF-8