print lines matching a pattern

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.

-R, -r, --recursive
       Read all files under each directory, recursively; this is equivalent to the -d recurse option.

-C NUM, -NUM, --context=NUM
       Print NUM lines of output context.  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.