Consider something like this.

#!/usr/bin/perl

use strict;

my %continent_of;

while( <DATA>) {
    my ($key) = (split /:/)[0];
    $continent_of{$key}++;
}

print join "\n", sort keys %continent_of;

__DATA__
Europe:Germany
Europe:France
Asia:India
Europe:Italy
Asia:Japan
Asia:Indonesia
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