I found this thread when trying to answer the same question. As rob_au suggested, I tried Geo::IP but my ISP doesn't support it (they have the module, but it needs a separate database file that has to be updated). I didn't have the necessary expertise to install the current version (it comes with a C library) and I couldn't make Geo::IP::PurePerl work. In the end I plumped for Geo::IPFree which I installed without trouble. It has a slightly simpler interface if all you want is to extract the country name and short code:

use CGI;
use Geo::IPfree qw(LookUp);
my ($countrycode,$country) = LookUp($cgi->remote_host);
print $countrycode,"\n",$country;
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Returns, for example:

GB
United Kingdom
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§ George Sherston