Setting a property based on the OS

[Kurien Mathew]

Is it possible to set a property based on the OS?

For eg consider the following folder setup

redist
 |- win32
 |- mac
 |- linux

I would like to set a property ${redistdir} based on the OS and then use it
to copy redistributable files from the relevant folder.

If there is a better way to accomplish this. Please let me know.