General :: File Association For Desktop Environment

With a desktop environment, there are file associations that goes with it. I'm a minimalistic user, who doesn't use any of such, but still want some kind of file associations to ease my burden. So I'm searching for a program that does something like the following. open file.pdf this will look at the extension, and translate to okular file.pdf. Of course one can always write a bash script to do this. I wonder if there is something existing, so I don't reinvent the wheel.