A straight forward way to do an intersection of two arrays (provided their elements are scalar values) is to create a hash using one array, where the keys correspond to the elements of that array. Then run over the other array, and if a key in the original hash corresponds with an element (i.e., it exists) then you've found an element in common.

The following solutions ensures all unique items in the intersection, even if both arrays contain duplicate items:

my @array1 = qw/a a b b c c d d/;
my @array2 = qw/        c c d d e e f f g g/;
my @array3 = ();
my %filter = ();

foreach (@array1) {
  $filter{$_} = 1;
}
foreach (@array2) {
  if (exists($filter{$_}) && 2 == ++$filter{$_}) {
    push(@array3,$_);
  }
}
print join(' ',@array3);
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If your arrays are do not contain scalar values, i.e., array/hash/sub refs, etc; then you can write a function to pass $_ through to serialize it first.