my %hash2 = (
            a_b__ca => {comment => 'abca', para1 => 1, para2 => 2},
            a_b__cb => {comment => 'abcb', para1 => 7, para2 => 2},
            a_b__cc => {comment => 'abcc', para1 => 4, para2 => 2},
            a_b__cd => {comment => 'abcd', para1 => 9, para2 => 2},
        );