Regular Expressions Cheat Sheet

A one-page regex reference: anchors, character classes, quantifiers, groups, lookarounds and flags, with an example for each. Syntax follows PCRE, which PHP, JavaScript and most editors share for everything below.

Anchors

Token	Matches	Example
^	Start of string (or line with m)	^Hello
$	End of string (or line with m)	world$
\b	Word boundary	\bcat\b matches “cat”, not “concat”
\B	Not a word boundary	\Bcat matches “concat”

Character classes

Token	Matches	Example
.	Any character except newline	a.c matches “abc”
\d / \D	Digit / not a digit	\d{4} matches “2026”
\w / \W	Word character [A-Za-z0-9_] / not	\w+
\s / \S	Whitespace / not	\s+
[abc]	One of a, b, c	gr[ae]y
[^abc]	Anything but a, b, c	[^0-9]
[a-z]	A range	[A-Fa-f0-9]

Quantifiers

Token	Matches	Example
*	0 or more	ab*
+	1 or more	\d+
?	0 or 1	colou?r
{n} / {n,} / {n,m}	Exactly n / n or more / n to m	\d{2,4}
*?, +?, ??	Lazy versions: match as little as possible	<.+?>

Groups and lookarounds

Token	Matches	Example
(abc)	Capturing group	(\d+)-(\d+)
(?:abc)	Group without capturing	(?:https?://)?
(?<name>abc)	Named group	(?<year>\d{4})
a|b	a or b	cat|dog
\1	Back-reference to group 1	(\w)\1 matches “ll”
(?=abc) / (?!abc)	Followed / not followed by	\d+(?= px)
(?<=abc) / (?<!abc)	Preceded / not preceded by	(?<=\$)\d+

Flags

Flag	Effect
i	Case-insensitive
g	All matches, not just the first (JavaScript)
m	^ and $ match at line breaks
s	. also matches newline
u	Unicode mode
x	Ignore whitespace in the pattern (PCRE)

Source from: addedbytes.com