There was a time when I worked with non utf-8 coded files quite a lot. They were usually saved using Windows-1250 encoding and obviously I wanted them in utf-8. I think I don’t need to tell you that you should probably use iconv for that, but there is also quite interesting tool called sponge that will allow you to pipe output of iconv to the very same file. In ubuntu it comes with packed called moreutils (also check out other apps it provides!