foreach my $e (@array1, @array2) {
    $union{$e}++ && $intersect{$e}++
}

##</code><code>##

my @sets = (\@array1, \@array2, ...);
for my $i (0..$#sets) {
  for my $j ($i+1..$#sets) {
    compute_stuff($sets[$i], $sets[$j]);
  }
}

##</code><code>##

sub union_intersection {
  my ($set1, $set2) = @_;
  my (%union, %intersection)
  for my $e (@$set1, @$set2) { ... }
  ...
}