Your problem is the line

foreach my $hashKey (sort keys $hash{$processKey})
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$hash{$processKey} is a reference to a hash and keys requires an actual hash. Therefore, all you need to do is to dereference the hash reference before passing it to keys

foreach my $hashKey (sort keys %{$hash{$processKey}})
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It's also worth pointing out that had you been running with -w and use strict then perl would have told you what the problem was.