How to convert an XML file produced by RSS feed to a file in Atom format?

[shealg]

I have an XML file (obviously) which is the output of an RSS feed. I would like to convert that file to the Atom format.There are plenty of Q&A's on StackOverflow about converting feeds, but I want to convert a file.I expect this is going to involve XSLT, but that is beyond me, and it's possible that such a converter already exists. Can anyone point me in the right direction?Thanks!