Regular expressions
From Programmer's Wiki
Regular expressions are string expressions which are used to identify matching patterns in other strings. Many languages and environments implement regular expressions, often with small differences. Regular expressions first gained large-scale use on unix systems in conjunction with tools such as grep, awk, and sed.
[edit] Simple Examples
Example 1. literal (no special characters used)
hello
Matches the string "hello" only.
Example 2. any character. the "." character matches any character except newline (\n).
an.
Matches "an!", "and"
Example 3. zero-or-more characters. the "*" character matches any string zero or more of the character immediately preceding it.
hel*
Matches "he", "hel", "hellll"
