my @list = (1, 2, 3, 6, 9, 10, 13, 22, 20, 19, 15, 21);

printf "<=>: %s\n", join ",", sort { $a <=> $b } @list;
printf "cmp: %s\n", join ",", sort { $a cmp $b } @list;
printf "   : %s\n", join ",", sort @list;