Script to get subnets in CIDR notation for the selected countries

subnets.pl

#!/usr/bin/perl
# dnf install perl-Net
# wget ftp://ftp.ripe.net/ripe/dbase/split/ripe.db.inetnum.gz
# wget https://ftp.apnic.net/apnic/whois/apnic.db.inetnum.gz
# zcat ripe.db.inetnum.gz | ./subnets.pl RU BY
# zcat apnic.db.inetnum.gz | ./subnets.pl MN

use Net::CIDR qw(range2cidr);
use Symbol;
use strict;
use warnings;

my $fds = {};
my @countries = @ARGV;

die "Invalid specified country code\n" if grep {!/^[A-Z]{2}$/} @countries;

foreach (@countries) {
    $fds->{$_} = gensym;
    my $fname = "$_.subnets";
    open $fds->{$_}, "> $fname" or die "Cannot open $fname for write: $!\n";
}

undef $/;
++$|;
$_ = <STDIN>;

while (/inetnum:\s*(?<range>[^\n]+)\n.*?country:\s+(?<country>\w{2})/gsmx) {
    my $cidr = range2cidr($+{range});
    my $country = $+{country};
    if (~~@countries) {
        next unless scalar(grep { $+{country} eq $_ } @countries) > 0;
        my $fd = $fds->{$country};
        print $fd "$cidr\n";
    } else {
        print "$cidr\n";
    }
}