Regular Expression (e.g. regex)

Regular Expression is a filtering method used in many linux/unix commands.

Symbol	Use
a*	Zero or many As
.	Any Single Character
[abc]	Any single character of a, b or c
[^abc]	Any single character except a, b or c
[a-z]	Any single character between a and z
^{a-z]	Any single character not between a and z
[A-Za-Z]	Any single character between a and z or A and Z
a|b	Any string matching a or b
a?	zero or one of a
a+	one or more of a
a{n}	exactly $n$ of a, $n \in \mathbb{z}$
a{n, m}	between n and m of a, $n, m \in \mathbb{z}$
^	start of string
$	end of string