In computing, a regular expression is a specific pattern that provides concise and flexible means to 'match' (specify and recognize) strings of text, such as particular characters, words, or patterns of characters. Common abbreviations for 'regular expression' include regex and regexp. The concept of regular expressions was first popularized by utilities provided with Unix distributions, in particular the editor ed and the filter grep. A regular expression is written in a formal language that can be interpreted by a regular expression processor, which is a program that either serves as a parser generator or examines text and identifies parts that match the provided specification. Historically, the concept of regular expressions is associated with Kleene's formalism of regular sets, introduced in the 1950s.
Contributions by Billposer, Thore, and Bluemoose.