Editing Regular expression (section)

{{Short description|Sequence of characters that forms a search pattern}}
{{Redirect|Regex|the comic book|Re:Gex{{!}}''Re:Gex''}}
{{Redirect|.*|the C++ operator|Pointer (computer science)#Pointer-to-member}}

[[File:Antony08.gif|thumb|upright=1.5|{{legend|#b0d0f0|outline=#b0d0f0|text=Blue|highlights show the match results of the regular expression pattern: <syntaxhighlight lang="ragel" inline>/r[aeiou]+/g</syntaxhighlight> (lower case ''r'' followed by one or more lower-case vowels).}}]]

A '''regular expression''' (shortened as '''regex''' or '''regexp'''),<ref>{{cite web |url=https://www.regular-expressions.info/tutorial.html |title=Regular Expression Tutorial - Learn How to Use Regular Expressions |last=Goyvaerts |first=Jan |website=Regular-Expressions.info |access-date=2016-10-31 |url-status=live |archive-date=2016-11-01 |archive-url=https://web.archive.org/web/20161101212501/http://www.regular-expressions.info/tutorial.html}}</ref> sometimes referred to as '''rational expression''',<ref name="Mitkov2003">{{cite book |last=Mitkov |first=Ruslan |title=The Oxford Handbook of Computational Linguistics |url=https://books.google.com/books?id=yl6AnaKtVAkC&pg=PA754 |date=2003 |publisher=Oxford University Press |isbn=978-0-19-927634-9 |page=754 |access-date=2016-07-25 |archive-date=2017-02-28 |archive-url=https://web.archive.org/web/20170228030346/https://books.google.com/books?id=yl6AnaKtVAkC&pg=PA754 |url-status=live}}</ref><ref name="Lawson2003">{{cite book |last=Lawson |first=Mark V. |title=Finite Automata |url=https://books.google.com/books?id=MDQ_K7-z2AMC&pg=PA98 |date=17 September 2003 |publisher=CRC Press |isbn=978-1-58488-255-8 |pages=98–100 |access-date=25 July 2016 |archive-date=27 February 2017 |archive-url=https://web.archive.org/web/20170227195128/https://books.google.com/books?id=MDQ_K7-z2AMC&pg=PA98 |url-status=live}}</ref> is a sequence of [[character (computing)|characters]] that specifies a [[pattern matching|match pattern]] in [[string (computer science)|text]]. Usually such patterns are used by [[string-searching algorithm]]s for "find" or "find and replace" operations on [[string (computer science)|strings]], or for [[data validation|input validation]]. Regular expression techniques are developed in [[theoretical computer science]] and [[formal language]] theory.

The concept of regular expressions began in the 1950s, when the American mathematician [[Stephen Cole Kleene]] formalized the concept of a [[regular language]]. They came into common use with [[Unix]] text-processing utilities. Different [[syntax (programming languages)|syntaxes]] for writing regular expressions have existed since the 1980s, one being the [[POSIX]] standard and another, widely used, being the [[Perl]] syntax.

Regular expressions are used in [[search engine]]s, in search and replace dialogs of [[word processor]]s and [[text editor]]s, in [[text processing]] utilities such as [[sed]] and [[AWK]], and in [[lexical analysis]]. Regular expressions are supported in many programming languages. Library implementations are often called an "[[software engine|engine]]",<ref>{{cite web |title=How a Regex Engine Works Internally |url=https://www.regular-expressions.info/engine.html |website=regular-expressions.info |access-date=24 February 2024}}</ref><ref>{{cite web |title=How Do You Actually Use Regex? |url=https://www.howtogeek.com/devops/how-do-you-actually-use-regex/ |website=howtogeek.com |date=11 March 2020 |access-date=24 February 2024 |author-first1=Anthony |author-last1=Heddings}}</ref> and [[comparison of regular expression engines|many of these]] are available for reuse.