Others have posted appropriate perl solutions to your sorting problem, which should be helpful -- and may even point to things you can do with perl that you can't do on the command line with the unix "sort" utility.

And folks are right -- this is a perl site, not a unix tool site (even though perl counts in many ways as a tool for unix users). Still, I can't resist pointing out that you are using the wrong options on the unix sort command line -- I think it would work as you intended if done like this:

 sort -k 3,3 -k 1,1n file
[download]

Reading all the way through the unix man page for "sort" should explain how the "-k" option is used. (Note that column indexes for "-k" start at 1, not at 0.)