I read that they stand for recursively in the man page. However, I am not sure what their role is in the command. When I tried to copy some empty directory into another directory with,
$ cp EMPDIR DESTDIR
it does not work, with error massage
cp: -r not specified; omitting directory 'empdir'
but when I executed
$ cp -r or -R EMPDIR DESTDIR
What is the exact function of -r and -R? Thank you for reading :)