-R, --dereference-recursive
For each directory operand, read and process all files in that directory,
recursively, following all symbolic links.
-r, --recursive
For each directory operand, read and process all files in that directory,
recursively. Follow symbolic links on the command line, but skip symlinks
that are encountered recursively. Note that if no file operand is given,
grep searches the working directory. This is the same as the
‘--directories=recurse’ option.