Thanks, this is exactly the kind of thing I was looking for. I'll likely end up stealing your sanity checks. :-)

As for your reply to Abigail-II's note, I am avoiding File::Temp for similar reasons. Even adding the extra checking you have here, my code will do far less and have a much smaller intended scope than File::Temp. Furthermore, I am not making temporary files, so using a module designed to do so seems to me kind of like using $#array+1 when I want scalar @array.