my %seen;

++$seen{$_} while <$fh_in1>;
--$seen{$_} while <$fh_in2>;

for (keys(%seen)) {
   print($fh_out1 $_) if $seen{$_} > 0;
   print($fh_out2 $_) if $seen{$_} < 0;
}

##</code><code>##

my %seen1; ++$seen1{$_} while <$fh_in1>;
my %seen2; ++$seen2{$_} while <$fh_in2>;

print $fh_out1 grep !$seen2{$_}, keys %seen1;
print $fh_out2 grep !$seen1{$_}, keys %seen2;