perldoc -q intersection

Found in C:\Perl\lib\pod\perlfaq4.pod
  How do I compute the difference of two arrays?  How do I compute the
+ intersection of two arrays?
            Use a hash. Here's code to do both and more. It assumes th
+at
            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 : \@
+difference }, $element;
                }

            Note that this is the *symmetric difference*, that is, all
            elements in either A or in B but not in both. Think of it 
+as an
            xor operation.
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