Elements in Regular Expressions

Expression	Description and Matching Examples
.	Any single character.
[abc]	Any single character enclosed in the brackets.
[^abc]	Any single character not enclosed in the brackets.
[a-z]	Any single character ranging from a thru z.
[0-9]	Any single digit.
(susan|mary)	susan or mary.
a?	Zero or one occurence of a.
a*	Zero or more occurence of a.
a+	One or more occurence of a.
^abc	A line led by abc.
abc$	A line terminated by abc.

Frequent-used Regexes

Email address: ^[\w-]+(\.[\w-]+)*@([\w-]+\.)+[a-zA-Z]{2,7}$
Float number: ^[+-]?\d+(\.\d*([Ee][+-]?\d+)?)?$
C++ identifier: ^[A-Za-z_][A-Za-z0-9_]*$
URL: ^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$