From perlman:perlfaq4:

How do I compute the intersection of two arrays?

Use a hash. Here's code to do both and more. It assumes that each element is unique in a given array:

@union = @intersection = @difference = ();
%count = ();
foreach $element (@array1, @array2) { $count{$element}++ }
foreach $element (keys %count) {
   push @union, $element;
   push @{ $count{$element} > 1 ? \@intersection : \@diff
erence }, $element;
}
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