Yep, that's what I wanted.

You would think that in the few weeks I've been learning Perl that I wouldn't have time to forget stuff like that. I know I read it in the Camel or the Lama, but I hadn't used it and - poof - gone. :-(

So the solution I was after is like this:

local($^I, @ARGV) = ('.bak', 'delme.txt');
print outFile while <>;
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