GNU grep, egrep and fgrep 'grep' is a utility to search for text in files; it can be used from the command line or in scripts. Even if you don't want to use it, other packages on your system probably will. The GNU family of grep utilities may be the "fastest grep in the west". GNU grep is based on a fast lazy-state deterministic matcher (about twice as fast as stock Unix egrep) hybridized with a Boyer-Moore-Gosper search for a fixed string that eliminates impossible text from being considered by the full regexp matcher without necessarily having to look at every character. The result is typically many times faster than Unix grep or egrep. (Regular expressions containing backreferencing will run more slowly, however.)