---

title: Regular expression

slug: Glossary/Regular_expression

page-type: glossary-definition

---

{{GlossarySidebar}}

**Regular expressions** (or _regex_) are rules that govern which sequences of characters come up in a search.

Regular expressions are implemented in various languages, but the best-known implementation is the Perl Implementation, which has given rise to its own ecosystem of implementations called PCRE (_Perl Compatible Regular Expression_). On the Web, {{glossary("JavaScript")}} provides another regex implementation through the {{jsxref("RegExp")}} object.

## See also