I have a bat script that I'd like to make work on windows/Mac/linux, but I read .bat is only for windows. How can I make this script work on Mac and linux, or what type of script can I write that would work on all 3.
If you don't want to step up to a language like C, I would suggest Python as a multi-platform scripting language. It's easy to learn and has lots of generic, multi-platform libraries and functions.
You'll need to install it on Windows, and maybe OS X as well. But it's not difficult in any way.