How do I do date math in a bash script on OS X Leopard?

Question

I realize I could whip up a little C or Ruby program to do this, but I want my script to have as few dependencies as possible.

Given that caveat, how does one d

Answer 1

For example, this OS X date command will add 14 days to the input string 20160826 (not the present time):

date -j -f %Y%m%d -v+14d 20160826 +%Y%m%d