Not working?

I think I must be missing something but this command isn't renaming the file specified... Pointers, tips appreciated! system("rename('/path/to/new.sh', '/path/to/old.$today')"); /to directory has permissions set to current user and is also owned by the current user (test_user)... I can write files into the directory and delete files form the directory using the 'unlink()' command but the rename function I am having problems with. Jas