grep, egrep, fgrep, rgrep, pgrep - are commands in Unix-like operating systems that print lines matching a pattern. The grep searches the named input FILEs for lines containing a match to the given PATTERN. By default, it prints the matching lines. In addition, the variant programs egrep, fgrep, and rgrep are the same as grep -E, grep -F, and grep -r, respectively. These variants are deprecated, but are provided for backward compatibility.