GNU grep is based on a fast lazy-state deterministic matcher 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.
1. To rapidly scan a large volume of information looking for a particular string or pattern. 2. A UNIX command used to scan a file or group of files for a matching search string or pattern.
The grep command lets you find lines in file(s) with particular text or regular expressions.