use diagnostics -verbose;

 while( my ( $key, $value ) = each %$data_a ){
      
    $data_b->{ $key } = $value
	
	}

 printf "%10s%12s\n", 'key:', ':value';

		
 while( my ( $k, $v ) = each %$data_b ){
    my $c;      
    printf "%9s%-8s%-11s\n", $k, ++$c % 2 == 1 ?  '  ---  ' : '', $v; 
	
	}


__END__   
      key:      :value
    house  ---   main
    first        Mary
   number  ---   0123
     area        north
 fullname  ---   Ms Mary Lou
     last        Lou
     code  ---   zip