regular expressions

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computing: software: programming: regular expressions

Overview

Regular expressions ("regex" for short) is a syntax used in string matching and replacement. It is especially heavily used in Perl, and the Linux utility grep is basically a front end for regex geared towards file-searching.

Articles

• Perl regex
• regex manpage

Examples

• \[http://[a-z|0-9|\.|\-]+\.[a-z|0-9|.|\-]+[a-z|0-9|\.|\-\/]* [a-z|0-9| ]+\]( )*
  • matches a link in MediaWiki markup (it could probably be more precise, but catches most of them)
• (\[http://[a-z|0-9|\.|\-]+\.[a-z|0-9|.|\-]+[a-z|0-9|\.|\-\/]* [a-z|0-9| ]+\]( )*){5,}
  • matches at least 6 links in a row with nothing except spaces between them; good for detecting spam

Links

Reference

• Wikipedia
• Regular-Expressions.info

Posts

• 2008-04-01 Regex in a Nutshell: small collection of links including a how-to, two online testers, and a "cheat sheet" PDF
• 2006-02-19 Visualizing Regular Expressions: blog entry by the author of reAnimator, a regex implementation visualizer