I can only think of two minor potential problems with $0.

Firstly, there are many circumstances where it can end up holding a relative path to the script, rather than an absolute one. If you then chdir, the relative path won't make sense. So don't do that.

Secondly, $0 is meaningless when perl is interpreting standard input. So don't do that either.

Other than that, I think you're golden. By definition the current process *must* have sufficient permission to read the script file, or it can't run it. So unless there's some bizarre suid situation I'm not considering, it should always be safe to open.