Grep

Grep is a command line utility originally created for the Unix operating system. It searches files for a word or pattern of characters.

Its input is a list of files (or current directory by default) and a text string or set of regular expressions. Its output consists of lines of text in the given files that match the string or regular expressions. The name "grep" stands for "Global Regular Expression Parser."

Grep is one of the most popular Unix utilities, and has been copied by many other operating systems.