Regex Patterns

Regular Expression, or regex in short, is a sequence of characters that specifies a search pattern in text.

This page shows a summary of regex constructs.

Characters

Pattern	Description	Example	Sample Match
.	Match any character	file..5	file_15
\d	A digit: [0-9]	file_\d\d	file_15
\D	Not a digit:[^0-9]	file_\D\D	file_ab
\w	A word character: [a-zA-Z_0-9]	\w-\w\w\w	A-b_1
\W	Not a word character	a\W\W	a-+
\s	A whitespace character.	a\sb	a b
\S	A non-whitespace character	a\Sb	a-b
\	Escapes special character	a\.b	a.b

Character classes Using []

Pattern	Description	Example	Sample Match
[abc]	a, b, or c	hell[AEIOU]	hellO
[^abc]	Any character except a, b, or c (negation)	hell[^aeiou]	hell_
[x-y]	character in the range from x to y	[A-Z]+	GREAT
[^x-y]	character not in the range from x to y	[^A-Z]+	great

Quantifiers

Pattern	Description	Example	Sample Match
+	One or more	\d+	12345
?	zero or one	hello!?	hello
*	Zero or more	AB*	ABBB
{N}	N times	x-\d{2}	x-12
{N1,N2}	N1 to N2 times	x-\d{2,4}	x-123

Logical operators and groups

Pattern	Description	Example	Sample Match
XY	X followed by Y	Hello	Hello
X|Y	Either X or Y	this is (true|false)	this is true (captures true, see bellow)
(X)	X, as a capturing group	I ate (\w+) at lunch	I ate carrots at lunch (captures carrots)
(?:X)	X, as a non-capturing group	this is (?:true|false)	this is true (without capturing true)
\1	Contents of Group 1	r(\w)g\1x	regex
\2	Contents of Group 2	(\d\d)+(\d\d)=\2+\1	12+65=65+12

Boundary matchers

Pattern	Description	Example	Sample Match
^	Start of line. (But when [^inside brackets], it means "not")	^abc .*	abc (line start)
$	End of line	.*? the end$	this is the end
\A	Beginning of string	\Aabc[\d\D]*	abc (string start)
\Z	The end of the input	the end\Z	this is...\n...the end\n
\G	The end of the previous match
\b	Word boundary	Bob.*\bcat\b	Bob ate the cat
\B	Not a word boundary	c.*\Bcat\B.*	copycats

Note

We follow java conventions for regex patterns, see java documentation for more info.