I could be wrong, as I only learned about the concept of a quine recently. But the way I understand it, it is good enough to simply output it. I suppose you could write to a file as well, but where would you write to? The wikipedia page for a quine has a lot of examples and all of them seem to simply output to stdout, just as I did. I don't think the challenge talks at any point about I/O, so I do think you can use it if you would want to.