This is pathetically simple, but I might develop it into something more useful.

{(current date) - (1 * weeks), (current date) - (4 * weeks)}

I can't find it. man cal says "command appeared in FreeBSD 2.2.6" which is since like 1998. Pretty sure it was working on whatever flavor of 10.6 I was last using. Also, related, is there a simple way to dope which build of Darwin I'm rocking? Also, would like to see a detailed list of feature upgrades to see what else I've missed.