print lines matching a pattern

-B NUM, --before-context=NUM
       Print NUM lines of leading context before matching  lines.   Places  a  line  containing  a  group
       separator  (--) between contiguous groups of matches.  With the -o or --only-matching option, this
       has no effect and a warning is given.

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.