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my %present;
for my $a ( @array1, @array2, @array3 ) { $present{ $a }++ }
my @only_two = grep $present{ $_ } == 2, keys %present;

use List::MoreUtils qw(uniq);
my %present = ();
for my $a ( uniq(@array1), uniq(@array2), uniq(@array3) ) { $present{ 
+$a }++ }
my @only_two = grep $present{ $_ } == 2, keys %present;