Regular Expression Reference on a Mouse Mat * PHP training
POSIX details * Perl details * Java details

PHP offers you two complete regular expression handlers. Functions such as ereg and eregi use POSIX style matching, and functions such as preg_match use Perl 5 style matching. How to choose which to use? New users tend to go with ereg and friends, and the geeks who want as much power as they can muster in as few characters as possible go to preg_match.

Go to the Perl regular expression page if you would like details of Perl style regular expressions; the following table refers to regular expressions as used in ereg (which is case signifgicant) and eregi (which ignores case).

Operator Type	Examples	Description
Literal Characters Match a character exactly	a A y 6 % @	Letters, digits and many special characters match exactly
	\$ \^ \+ \\ \?	Precede other special characters with a \ to cancel their regex special meaning
	\n \t \r	Literal new line, tab, return
	\cJ \cG	Control codes
	\xa3	Hex codes for any character
Anchors and assertions	^	Starts with
	$	Ends with
Character groups any 1 character from the group	[aAeEiou]	any character listed from [ to ]
	[^aAeEiou]	any character except aAeEio or u
	[a-fA-F0-9]	any hex character (0 to 9 or a to f)
	.	any character at all (not new line in some circumstances)
	[[:space:]]	any space character (space \n \r or \t)
	[[:alpha:]]	any letter
	[[:digit:]]	any digit
	[^[:space:]]	any character that is NOT a space
Counts apply to previous element	+	1 or more ("some")
	*	0 or more ("perhaps some")
	?	0 or 1 ("perhaps a")
	{4}	exactly 4
	{4,}	4 or more
	{4,8}	between 4 and 8
	Add a ? after any count to turn it sparse (match as few as possible) rather than have it default to greedy
Alternation	|	either, or
Grouping	( )	group for count and save to variable
	(?: )	group for count but do not save

The above list show the most commonly used elements of PHP (POSIX) regular expressions, and is not exhaustive.

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