[JNRowe]

If you're looking for a general solution to that specific type of problem, then dateutils¹ is really useful. It deals with conversions, durations, matching, repeats, etc. It also has a clear and well defined date input format, and being a collection of command line tools it is easy to mangle it in to other tools.

¹ http://www.fresse.org/dateutils

[indentit]

thanks for the recommendation, I hadn't come across this before and it looks really useful!