Makes me think in this way. Not sure if I miss anything. 
my @non_unique;
(in_array($_,\@temp)) && (push @non_unique, $_)  for (@temp2);

sub in_array {
   ($_ eq $_[0]) && (return $_) for (@{$_[1]})  ;
}

[download]
Thanks.

In reply to Re: Compare Lists (Non Unique Intersection) by Mandrake
in thread Compare Lists (Non Unique Intersection) by rsiedl

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