push (@{%newhash->{$rows[0]}}, @newrows);
push (@{%newhash->{$rows[0]}}, @newrows);

##</code><code>##

push @{$newhash{IP}}, @newrows);
push @{$newhash{IP}}, @newrows);

##</code><code>##

push @{$newhash{IP}}, [@newrows]);
push @{$newhash{IP}}, [@newrows]);

##</code><code>##

$VAR1 = {
          'IP' => [
                    [
                      'value1',
                      'value2'
                    ],
                    [
                      'value1',
                      'value2'
                    ]
                  ]
        };

##</code><code>##

@printrows = $newhash{$key}; # wrong -> the hash will contain a reference to an array
@printrows = @{$newhash{$key}}; # right -> de-reference the array first