answer for "ref ... and ... っていうのは何がしたい？"

ref_and_undef.pl

use strict;
use warnings;
use Data::Dumper;

### case of scalar
{
    my $data = 123;
    ref $data and $data = undef;
    print Dumper({'SCALAR' => $data});
};

### case of reference
{
    my $data = { hoge => 'fuga' } ;
    ref $data and $data = undef;
    print Dumper({'HASHREF' => $data});
};

$VAR1 = {
          'SCALAR' => 123
        };
$VAR1 = {
          'HASHREF' => undef
        };