Short for regular expression; a sequence of characters that defines a search pattern for text processing.
Abbreviation of 'regular expression', a term from formal language theory developed by mathematician Stephen Kleene in the 1950s. 'Regular' refers to regular languages in computational theory, not the common meaning of 'normal'. The concept was implemented in programming languages starting with Perl.
Regular expressions are simultaneously one of programming's most powerful and most feared tools - they can solve complex text problems in a single line but look like cryptic hieroglyphics to the uninitiated. The joke goes: 'Some people have a problem and decide to use regex. Now they have two problems.'
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