foreach $input (@in) { $data{$input}++ }
foreach $db (@db) { $data{$db}++ }
@db = [];
foreach $value (keys %data) {if ($data{$value}) = 1 {push @db $value} }


What does this do?


Assuming @in = 1,3,5 and @db = 3, 5, 6
First foreach %data = { 1=>1, 3=>1, 5=>1}
Second foreach %data = { 1=>1, 3=>2, 5=>2, 6=>1}


Now when the lists are combined, all keys with values
equal to 1 only occurs once, any keys that have values
greater than 1 occur in both lists.