DB<4> $h{a}{b}=[1,2]; $h{a}{c}=[3,4]  #hash with two elements (arrays) and in 2 levels

  DB<5> use Data::Dumper  #good way to display 

  DB<6> p Dumper\($a,%h)
$VAR1 = \undef;
$VAR2 = {
          'a' => {
                   'c' => [
                            3,
                            4
                          ],
                   'b' => [
                            1,
                            2
                          ]
                 }
        };

  DB<7> p 'da' if !$h{p}{m}  #checking for an existent keys and element
da
  DB<8> p Dumper\($a,%h)
$VAR1 = \undef;
$VAR2 = {
          'p' => {},            # <<== created one !!!
          'a' => {
                   'c' => [
                            3,
                            4
                          ],
                   'b' => [
                            1,
                            2
                          ]
                 }
        };

  DB<9> delete $h{p}