Thanks Ken - seeing a working example is extremely helpful.

My first thought is that I would need to use a pipe but then realised that there doesn't seem to be anything to pipe to...

You are right, I am using Perl v5.16 (still not moved toa VPS). I will try it without writing out and deleting a file some time but it is not a very high priority as the thing now works and will only get used a couple of times each month. Speed is not at all important - it could take half an hour, and it would still be acceptable.