How do I do date math in a bash script on OS X Leopard?
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 do date math in a bash script on OS X? I've seen a post (on another site) where someone did the following:
date -d "-1 day"
But this does not seem to work on OS X.
Addendum:
Several people have commented and responded that Ruby, Python, Perl, and the like come standard with OS X. I'm familiar with all three of these languages and could easily write a script that does what I want. As a matter of fact, I already have such a script, written in Ruby.
So perhaps I should clarify what I mean by 'external dependency'. What I mean is, I don't want my bash script to have to call any other script external to it. In other words, I want it to use some utility available in a vanilla installation of OS X and already on the path.
However, it doesn't look like this is possible, so I will have to make due with my external dependency: a Ruby script.
Answer
$ date -v -1d
-d sets Daylight Savings time flag.
Try man date for more info.