regular expression (regex)

A regular expression (sometimes abbreviated to "regex") is a way for a computer user or programmer to express how a computer program should look for a specified pattern in text and then what the program is to do when each pattern match is found. For example, a regular expression could tell a program to search for all text lines that contain the word "Windows 95" and then to print out each line in which a match is found or substitute another text sequence (for example, just "Windows") where any match occurs.

The best known tool for specifying and handling the incidence of regular expressions is grep, a utility found in UNIX-based operating systems and also offered as a separate utility program for Windows and other operating systems.

This was last updated in January 2006

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