Concepts

Regular Expression

Notation

Citation Formats

General Reference

Computing Atlas. "Regular Expression." Accessed August 30, 2026. https://computing.interactiveatlas.org/concepts/regular-expression.

APA Style

Computing Atlas. (n.d.). Regular Expression. Retrieved August 30, 2026, from https://computing.interactiveatlas.org/concepts/regular-expression

BibTeX

@misc{computingatlas-regular-expression,
  author = {Computing Atlas},
  title = {Regular Expression},
  year = {2026},
  url = {https://computing.interactiveatlas.org/concepts/regular-expression},
  note = {Accessed August 30, 2026}
}

A sequence of characters defining a search pattern, grounded in Stephen Kleene's 1951 mathematical formalization of regular languages (his own term was regular events), work motivated by the same McCulloch-Pitts neural-net formalism behind the finite-state machine. Ken Thompson, already a pioneer entity on this atlas, implemented Kleene's notation practically in the QED text editor around 1968 using what became known as Thompson's construction algorithm, later carrying it into the Unix editor ed; the word grep descends directly from ed's own g/re/p command (global search for a regular expression, then print), a verified etymology rather than a repeated folk claim.

Facts

Origin Year

1951 1

Core Principle

A pattern written in a small algebraic notation (concatenation, alternation, repetition) that denotes a regular language, which Thompson's construction algorithm converts into an equivalent finite-state automaton for actual matching. 1

Cross-Tradition Connections