@oldstock = ("widgets:10:5",
             "wodgets:4:2",
             "spanners:5:3");

@newstock = ("screwdrivers:8:3",
             "hammers:5:1",
             "widgets:3:1");

##</code><code>##

@totalstock = ("widgets:13:6",  # Both widget entries joined
               "wodgets:4:2",
               "spanners:5:3",
               "screwdrivers:8:3",
               "hammers:5:1");

##</code><code>##

my %stock = ();
my %shown = ();

# Build our records

foreach my $record (@newstock @oldstock) {
    my ($name, $stock, $shown) = split(/:/$record);
    $stock{$name} += $stock;
    $shown{$name} += $shown;
}

# Print the result.

foreach my $name (keys %stock) {
    print join(":",$name,$stock{name},$shown{name}),"\n";
}