grep is a command line text search utility originally written for Unix. The name is taken from the first letters in global / regular expression / print, a series of instructions for the ed text editor. The grep command searches files or standard input globally for lines matching a given regular expression, and prints them to the program's standard output.

This is an example of a common grep usage: In this case, grep prints all lines containing 'apple' from the file fruitlist.txt, regardless of word boundaries; therefore lines containing 'pineapple' or 'apples' are also printed. The grep command is case sensitive by default, so this example's output does not include lines containing 'Apple' (with a capital A) unless they also contain 'apple'.

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