Skipping duplicate cities and regexp

#!/usr/bin/perl -w
use strict;
use Data::Dumper;


my $country; # Hash ref ;)
my $sep = q{,};

while (<DATA>) {
    chomp;
    next if /\A\z/;
    /\s* (.+) \s* $sep \s* (.+) \s*/msx;
    next unless defined $1 and defined $2; 
    grep { /$1/i } @{ $country->{$2} } 
      or push @{ $country->{$2} }, $1; 
}

print Dumper $country;

__DATA__

Chicago, USA
Frankfurt, Germany
Berlin, Germany
Washington, USA
Helsinki, Finland
Berlin, Germany
New York, USA
Freetown, Sierra Leone
[download]

hth,
PooLpi