grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]
grep searches the named input FILEs (or standard input if no files are
named, or if a single hyphen-minus (-) is given as file name) for lines
containing a match to the given PATTERN. By default, grep prints the
matching lines.
In addition, two variant programs egrep and fgrep are available. egrep
is the same as grep -E. fgrep is the same as grep -F. Direct
invocation as either egrep or fgrep is deprecated, but is provided to
allow historical applications that rely on them to run unmodified.