{
    my %hash = (
        'Ask'   =>  1,
        'Bob'   =>  1,
        'Cat'   =>  1,
        'amy'   =>  1,
        'ben'   =>  1,
        'can'   =>  1,
    );

    print join "\n", sort case_sorter keys %hash;
}

sub case_sorter {

    my $first_a = substr $a, 0, 1;
    my $first_b = substr $b, 0, 1;

    if ( ($first_a eq uc($first_a)) && ($first_b eq uc($first_b)) ) {
        return $a cmp $b;
    }
    elsif ( $first_a eq uc($first_a) ) {
        return 1;
    }
    elsif ( $first_b eq uc($first_b) ) {
        return -1;
    }
    else {
        return $a cmp $b;
    }
}