my %convert = (
        to_currency => { US => 'USD',
                         USA => 'USD',
                         MR => 'MRD',
                         MARS => 'MRD',
                       },
        to_country => { US => 'USA',
                        USD => 'USA',
                        MR => 'MARS',
                        MRD => 'MARS',
                       },
        to_code => { USA => 'US',
                     USD => 'US',
                     MARS => 'MR',
                     MRD => 'MR',
                    },
);

my $code = 'US';
print "$code currency is: $convert{to_currency}{$code}\n";
print "$code country is: $convert{to_country}{$code}\n";

my $currency = 'USD';
print "Code for $currency is: $convert{to_code}{$currency}\n";

my $country = 'MARS';
print "$country currency is: $convert{to_currency}{$country}\n";