Thanks to all, I've learnt a lot.

In my rush to try the code suggested by choroba, I failed to notice the second step, i.e. system sort, duh!.

I've tried it now and it seems good for my purposes - I liked that it seemed to be able to use all cores (showed 99% CPU usage, versus 12% for perl.exe which I assume is just one of my 8 cores). I'm off now to learn more about the sort command - I need it to recognise tab separation.

In reply to Re: What is the most memory efficient way to (sort) and print a hash? by a_salway
in thread What is the most memory efficient way to (sort) and print a hash? by a_salway

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