Perl Regular Expression Cheat Sheet

This document presents a quick tabular summary of the regular expression (regexp) syntax in Perl, with examples.

The methods used here are also the methods you will need for manipulating your htaccess files.

Meta Characters

To present a meta character as a data character standing for itself, precede it with \ (e.g. \. matches the full stop character .).

Char	Name (ISO 8859-1)	Unicode	HTML	Octal	Meaning
^	Circumflex accent	005E	^	136	beginning of string
$	Dollar sign	0024	$	44	end of string
.	Full stop	002E	.	56	any character except newline
*	Asterisk	002A	*	52	match 0 or more times
+	Plus sign	002B	+	53	match 1 or more times
?	Question mark	003F	?	77	match 0 or 1 times; or: shortest match
|	Vertical line	007C	|	174	alternative
( )	Left parenthesis Right parenthesis	0028 0029	( &#41	50 51	grouping; "storing"
[ ]	Left square bracket Right square bracket	005B 005D	[ ]	133 135	set of characters
{ }	Left curly bracket Right square bracket	007B 005D	{ ]	173 135	repetition modifier
|	Vertical line or bar	007C	|	174
\	Reverse solidus or backslash	005C	\	134	quote or special and escape notation

 

Repetition

a*	zero or more occurrences of string, each of which matches pattern a
a+	one or more occurrences of string, each of which matches pattern a
a?	zero or one occurrences of string, each of which matches pattern a (i.e., optional a)
a{m}	exactly m occurrences of string, each of which matches pattern a
a{m,}	at least m occurrences of string, each of which matches pattern a
a{m,n}	at least m but at most n occurrences of string, each of which matches pattern a
repetition?	same as any of the repetition expressions listed above but the shortest string matching the pattern is taken. The default is "greedy matching", which finds the longest match. (Perl version 5)

 

Special notations with "Backslash"

\t	tab
\n	newline
\r	return (CR)
\xhh	character with hex. code hh
\b	"word" boundary
\B	not a "word" boundary

 

Special Matching Notations

\w	matches any single character classified as a "word" character (alphanumeric or "_")
\W	matches any non-"word" character
\s	matches any whitespace character (space, tab, newline)
\S	matches any non-whitespace character
\d	matches any digit character, equiv. to [0-9]
\D	matches any non-digit character

 

Character Sets (Character Class) Denoted By […]

[characters]	matches any of the characters in the sequence
[x-y]	matches any of the characters x to y (inclusive) in the ASCII code
[\-]	matches the hyphen character
[\n]	matches the newline character, same for other single character denotations with \ (backslash)
[^something]	matches NOT something

 

Examples

abc	Find abc anywhere in the string.
^abc	Find abc at the beginning of the string.
abc$	Find abc at the end of the string.
a|b	Find either a OR b anywhere in the string.
^abc|abc$	Find abc at the beginning OR end of the string.
ab{2,4}c	Find an a followed by two, three or four b’s followed by a c.
ab{2,}c	Find an a followed by at least two b’s followed by a c .
ab+c	Find an a followed by one or more b’s followed by a c .
ab?c	Find an a followed by an optional b followed by a c.
a.c	Find an a followed by any single character except newline followed by a c.
a\.c	Matches exactly.
[abc]	Find either a OR b OR c.
\d{2}	Matches any two decimal digits, i.e. 42.
\w+	Matches a "word", a nonempty sequence of alphanumeric characters and underscores.

 

Many thanks to IT and communication (http://www.cs.tut.fi/~jkorpela/indexen.html) for the information contained within this cheat sheet.