Regular expressions – regex

Regular expression or regex ‘is a sequence of characters that specifies a search pattern. Usually such patterns are used by string-searching algorithms for “find” or “find and replace” operations on strings, or for input validation. It is a technique developed in theoretical computer science and formal language theory.’

From Wikipedia

Used in programming. See Learning regular expressions

Testing tools

Tools for visually testing your regular expressions. These tools are invaluable when you’re a regex novice like myself.