-r, which removes directories, removing the contents recursively beforehand (so as not to leave files without a directory to reside in) (“recursive”) - 不会出现警告信息
-i, which asks for every deletion to be confirmed (“interactive”) - 在删除前会询问用户是否操作
-f, which ignores non-existent files and overrides any confirmation prompts (“force”), although it will not remove files from a directory if the directory is write-protected. - 递归删除