in reply to hello who can help a newbie "me" with a perl file?...
We can help you with the Perl part, but the rest I think you're going to have to figure out yourself.
To run a task every 20 minutes you'll probably want to use cron; and you can use Perl's Net::Ftp module to connect to your ftp server, delete and upload files.
If this is coursework, perhaps there are notes or a text book that you can consult.
Alex / talexb / Toronto
Thanks PJ. We owe you so much. Groklaw -- RIP -- 2003 to 2013.