Regular-Expressions.info - Regex Tutorial, Examples and Reference - Regexp Patterns. Regular Expressions - a Simple User Guide. A Regular Expression is the term used to describe a codified method of searching invented, or defined, by the American mathematician Stephen Kleene.
The syntax (language format) described on this page is compliant with extended regular expressions (EREs) defined in IEEE POSIX 1003.2 (Section 2.8). EREs are now commonly supported by Apache, PERL, PHP4, Javascript 1.3+, MS Visual Studio, most visual editors, vi, emac, the GNU family of tools (including grep, awk and sed) as well as many others. Regular Expression Library.