Command-line-interface (CLI) calculator to work out the difference between 2 dates

["j t" <mark473@gmail.com>]

Hi all.

Does anyone have any suggestions for a command-line-interface (CLI)
calculator that can work out the difference between 2 (gregorian)
dates (i.e. that is calendar aware). My favourite cli calculator
("bc") doesn't seem to have any knowledge of the gregorian calendar.

Just to make it clear, I'd like to be able to type in:

20080824-20080724 and it would work out the answer as 31

(I'm happy to use any date format for input - I've only used ISO8601
as an example)

J :-)