Regarding %set2 = ( %set2, %set1 );, This unrolls the hashes into a temporary list which is fine unless your hashes are big. If they're really big, you may want to use

while ( ($k,$v) = each %set2 ){
    $set1{$k} = undef ; # or perhaps more useful, ++
}

# or to merge two and leave them both intact.
my %merged = ()
foreach $hashref ( \%set1, \%set2 ) {
    while (($k, $v) = each %$hashref) {
        $merged{$k} = $v;
    }
}
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-Lee

"To be civilized is to deny one's nature."