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Regular expressions, also known as regular expressions. (English: regular expression, often abbreviated as regex, regexp or re in code), a concept of computer science. Regular expressions are usually used to retrieve and replace text that conforms to a certain pattern (rule).

Many programming languages support string manipulation using regular expressions. Perl, for example, has a powerful regular expression engine built in. The concept of regular expression was first popularized by Unix tools such as sed and grep. Regular expressions are usually abbreviated as "regex", regexp and regex are singular, and regxps, regexes and regxen are plural.