“One of the issues that has long irritated Unix users when
setting up cron jobs is how to set up a job to run on the last day
of the month. Unless one wants to set up a separate cron job for
every month (and this still leaves the problem of leap years), it
isn’t at all straightforward how to attack this seemingly ordinary
problem with an ordinary solution. However, there are some reliable
ways to code around the problem. One long winded but workable way
to determine the last day of any month in any year is to string
together some well known Unix commands…”