when user presses a button, you can manage it to invoke a sub which, in turn, will do what I just said and return.

Here is oneliner for Win32 that will demonstrate what I just said:

perl -MTk -lwe "for(tkinit){$_->Button(-text=>'test',-command=>sub{pri
+nt'do anything you want here, i.e. call your favourite program'})->pa
+ck;$_->Text->pack};MainLoop"
[download]

OTOH there are quite a lot of examples of Tk programs here and there, so you can start using them right away.

Courage, the Cowardly Dog