in reply to date subtraction

There is. Have a look at the   Date   and   Time   modules on   CPAN.

I could have told you more, had you given me an example.

Update:
You find general examples in the Tutorials section of this site.

Pity me, no, there aren't any tutorials on the   Date   and   Time   modules (yet). Hint, hint...

Cheers, Sören