Here's some explanation for -r, -R, or -f and combination of -rf
OPTIONS The following options are supported for /usr/bin/rm and /usr/xpg4/bin/rm:
-r Recursively removes directories and subdirectories in the argument list. The directory will be emptied of files and removed. The user is normally prompted for removal of any write-protected files which the direc- tory contains. The write-protected files are removed without prompting, however, if the -f option is used, or if the standard input is not a terminal and the -i option is not used.
Symbolic links that are encountered with this option will not be traversed.
If the removal of a non-empty, write-protected direc- tory is attempted, the utility will always fail (even if the -f option is used), resulting in an error mes- sage.
-R Same as -r option
-f Removes all files (whether write-protected or not) in a directory without prompting the user. In a write- protected directory, however, files are never removed (whatever their permissions are), but no messages are displayed. If the removal of a write-protected direc- tory is attempted, this option will not suppress an error message.