kdb is available on Windows, Linux, Solaris and Mac OS X. Like most functional languages, q is a very high level language. As long as you stick with forward slashes in your file paths, you will be rarely notice the difference between operating systems. The only significant issue we’ve come across is that multi-threading is not supported on Macs.
If you do need to distinguish different operating systems, use the variable .z.o to detect the operating system in which your code is running.