my @old_stock1 = ('products','here');
my @old_stock2 = ('products','here');

# define hash to store quantities
my %new_stock;

# iterate through old
for (@old_stock1, @old_stock2) {

  # add one to count for this element
  # (creating it if it doesn't exist)
  $new_stock{$_}++;

}

##</code><code>##

for (keys %new_stock) {
  print "$_ = $new_stock{$_}\n";
}