regular expression

regular expression

? The question mark indicates there is zero or one of the preceding element. For example, colou?r matches both "color" and "colour".

* The asterisk indicates there are zero or more of the preceding element. For example, ab*c matches "ac", "abc", "abbc", "abbbc", and so on.

+ The plus sign indicates that there is one or more of the preceding element. For example, ab+c matches "abc", "abbc", "abbbc", and so on, but not "ac".

. Matches any single character

[ ] A bracket expression. Matches a single character that is contained within the brackets. For example, [abc] matches "a", "b", or "c". [a-z] specifies a range which matches any lowercase letter from "a" to "z".

[^ ] Matches a single character that is not contained within the brackets. For example, [^abc] matches any character other than "a", "b", or "c".

^ Matches the starting position within the string. In line-based tools, it matches the starting position of any line.

$ Matches the ending position of the string or the position just before a string-ending newline. In line-based tools, it matches the ending position of any line.

\( \) Defines a marked subexpression. The string matched within the parentheses can be recalled later (see the next entry, \n).

\{m,n\} Matches the preceding element at least m and not more than n times. For example, a\{3,5\} matches only "aaa", "aaaa", and "aaaaa". This is not found in a few, older instances of regular expressions.

Reference :
http://en.wikipedia.org/wiki/Regular_expression
http://gnosis.cx/publish/programming/regular_expressions.html