Web Standards Programmer's Reference: HTML, CSS, JavaScript®, Perl, Python®, and PHP

D.7. Regular Expressions

The following tables provide information used with Perl's regular expressions and regex handling functions.

D.7.1. Matching Expressions and Characters

Expression/Character	Use
.	Matches an arbitrary character but not a newline.
(...)	Groups a series of elements into a single element; that single element can be used as subexpressions (later referenced with $1 to $9 or \1 to \9, if matched).
^	Matches the beginning of a line or the beginning of the pattern.
$	Matches the end of a line.
[ ... ]	Matches a class of characters. Use ^ to negate the class ( [^ ... ] ).
( ... | ... | ... )	Matches one of the alternatives.
\character	Escape character.
(?# text )	Use text as a comment.
(?: regexp )	Similar to (regexp) but does not make back-references.
(?= regexp )	Zero width, positive look-ahead assertion.
(?! regexp )	Zero width, negative look-ahead assertion.
(? modifier )	Embedded pattern-match modifier. The modifier can be one or more of the following: i, m, s, or x.

D.7.2. Match Count Modifiers

Modifier	Use
+	Matches the preceding character or pattern element one or more times.
?	Matches the preceding character or pattern element zero or one times.
*	Matches the preceding character or pattern element zero or more times.
{N,M}	Matches the preceding character or pattern element a minimum of N and maximum of M match count. Use {N} for exactly N matches; use {N,} for at least N matches.

D.7.3. Escape Characters

Escaped Character	Use
\w	Matches alphanumeric (including underscore).
\W	Matches nonalphanumeric. ...