Regular Expressions are an exceptionally flexible way of matching patterns in modern programming languages. They originate in the grep utility of early Unix days - "grep" stands for "Global Regular Expression Processor" when it was realised that the alterntive globbing technology lacked the extensibility that was desirable. Grep turned out to be such an excellent tool that other facilities were quickly added in egrep ("Extended grep").

With the advent of Perl, extra facilites were needed and still further extensions were made to regular expressions. Since the Regular Expression engine is built into each appliaction, though, a number of different flavours were developing ... and there was a view in some quarters that the Perl syntax was too terse to be understandable. Thus was born the "competing" POSIX Style of regular expressions.

.Open source is all about sharing ideas and technologies for the greater good of all, and these days, Perl supports the POSIX extensions too and languages like PHP include both a POSIX and a Perl compatible regular expression library.

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Associated topic - Object Orientation and General technical topics - What are Regular Expressions?

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