If you find yourself "uniquifying" keys for a hash you should probably be using an array. Consider:

use strict;
use warnings;

use constant KEY => 1;

my @sort_data;
while (my $record = <DATA>) {
    my $key = (split(/,/, $record))[KEY];
    push @sort_data, [$record, $key];
}

foreach my $pair (sort {$a->[1] cmp $b->[1]} @sort_data) {
    print "$pair->[0]";
}
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using the same data as in previous samples prints:

BUT, It runs with no errors, but nothing prints.
I tried your code, and it seems quite simple, hence, efective.
At the moment, due to the small file size, sort time is unimportant.
At some point, when I get to that stage, the sorted data will be reuse
+d.
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