UNIX date manipulation with yest

Somebody's finally written a version of the classis UNIX program date that can handle simple arithmetic operations. yest appears to be the tool that lets you print yesterday's date, or 90 days from now.

In completely related news, I'm thinking about updating my rent-paying reminder application to notify me before the last Saturday of the month. This way I'll know in advance when I will be able to deliver the check to my leasing office in person. Some ideas:

Play with yest; rewrite the damn thing in three lines of Python; refactor the damn thing in C to use some sort of day-of-the-week-checking loop (provided I can still track down the source code); other? The sky's the limit here. I could write some kind of uberscript in Perl or Ruby, but it would be hard to justify it to myself.