You really need to explain your question better because it is hard to understand what exactly you are asking... but I am going to give two tries...

1) If you mean that you need your script to run once a day over 31 days, well then it sounds like you need to check out "cron" on your system -- this is not a Perl specific item.

2) If you are looking to populate a drop-down list of 31 days from the present, then you might want to check out the Date::Calc library which has some nice date calculation routines. You can search for it on cpan.org.

Good Luck