print lines matching a pattern

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

Other Options
    --line-buffered
           Use line buffering on output.  This can cause a performance penalty.

-H, --with-filename
       Print  the  file  name  for  each  match.  This is the default when there is more than one file to
       search.

-l, --files-with-matches
       Suppress normal output; instead print the name of each input file from which output would normally
       have been printed.  The scanning will stop on the first match.  (-l is specified by POSIX.)