grep 3.4 Print lines matching a pattern
grep is a tool for finding text inside files. Text is found by matching a pattern provided by the user in one or many files. The pattern may be provided as a basic or extended regular expression, or as fixed strings. By default, the matching text is simply printed to the screen, however the output can be greatly customized to include, for example, line numbers. GNU grep offers many extensions over the standard utility, including, for example, recursive directory searching.