sort needs both time and space to perform the sort no matter how cleverly implemented. I find it hard to imagine a system that is so poorly configured that it can't handle sorting a paultry 500kB file. But I don't think that really matters in this particular case.

There is a reason that "sort -u" came to be. It is much slower to sort all 57000 instances of several IPs and then throw all but one of each away. So I think "sort | uniq -c" would be much slower than using Perl.

Unfortunately, it doesn't appear that even GNU sort has bothered to implement a -u option that counts the duplicates.

Thanks for making me realize a typo.
The file that I am parsing is 500MB, not 500kB....
That's why sort freaks out.