I wonder if this is what you are aiming to do.

use strict;
use warnings;

use Data::Dumper;

my %continents;
while ( <DATA> )
{
    chomp;
    my( $continent, $country ) = split m{:};
    push @{ $continents{ $continent } }, $country;
}

print Data::Dumper->Dumpxs(
   [ \ %continents ],
   [ qw{ *continents } ]
   );

__DATA__
Europe:Germany
Europe:France
Asia:India
Europe:Italy
Asia:Japan
Asia:Indonesia
[download]

The output.

%continents = (
                'Europe' => [
                              'Germany',
                              'France',
                              'Italy'
                            ],
                'Asia' => [
                            'India',
                            'Japan',
                            'Indonesia'
                          ]
              );
[download]

I hope I have guessed correctly and this is of some help.