Grep

grep is a command line utility originally written for use with the Unix operating system. The default behaviour of grep takes a regular expression on the command line, reads standard input or a list of files, and outputs the lines containing matches for the regular expression.

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The name comes from a command in the Unix text editor ed that takes the form:

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:g/re/p

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This means "search globally for matches to the regular expression re, and print lines where they are found". There are various command line switches available when using grep that modify the default behaviour.

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Command line: REDIRECT Command-line interface...

Regular expression: A regular expression (abbreviated as regexp, regex, or regxp, with plural forms regexps, regexes, or regexen) is a string that describes or matches a set of strings, according to certain syntax rules. Regular expressions are used by many text editors and utilities to search and manipulate bodies of ...

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