Thanks! That is exactly what I needed. I didn't know the difference between a LIST and an ARRAY. I guess I still need to learn about it, but your solution for an anonymous array reference is exactly what I was looking for.

Thanks a million.

Here is my final code, for what it is worth. Yes, I needed to reinvent the wheel for portability, since getting List::MoreUtils is not an option...

sub compare {
  my @refs = @_;
  my ($all, $inter, $diff);
  my %files;
  foreach my $ref (@refs) {
    foreach (@$ref) {
      $files{$_}++;
    }
  }
  $all = [ keys %files ];
  foreach my $e (@$all) {
    push @{ $files{$e} > 1 ? $inter : $diff }, $e;
  }
  return ($all, $inter, $diff);
}
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