my @numbers = (15,5,7,3,9,1,20,13,9,8,
    15,16,2,6,12,90);
printf ('The maximum number is %s%s', max(@numbers), "\n");

sub max {
    my $first = shift;
    while ($#_ >= 0) { # until list exhausted
        if ($first >= $_[0]) { # keep throwing away inferiors
            shift;
        }
        else {
            $first = shift; # crown the new king
        }
    }
    return $first; # end of list, inferiors exhausted
}