Trying to write a shell script with someone else (for the first time for me), thought to myself:
What would I do on Windows as an equivalent?
And I came up with a Javascript solution. Now thinking further I thought: Why not try to write a script that will run within the Windows Scripting Host, the .NET CLR and a browser?
The funny thing is: You can actually write such a script. The only thing (with such a simple script) that differs is IO. But thanks to Javascript´s try - catch (Which I hadn´t known of until three weeks ago, and I have done a lot of JS), that is not a problem either.
You can take a look at the script
here. It´s nothing spectacular, takes a date, adds X days an returns the new date, all without the Date object (I did the script as a pre-version of the shell script, so I kept all the fancy stuff out).