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	good.morning	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 football	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

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