use Net::Whois::IP ('whoisip_query');  # This module is not installed automatically with a
                                        # Perl installation, so you'll need to install it 
                                        # from CPAN in order to be able to use its 
                                        # whois_ip_query function.

use Fcntl (':flock');

if ($userIP) {

    my $location_of_some_log_file = '/var/logs/my_log_file.log';

    open ( my $log_fh, '>> :encoding(UTF-8)', $location_of_some_log_file )
      or die "FATAL: Trouble opening '$location_of_some_log_file' for appending: $!";

    flock ( $log_fh, LOCK_EX );

    my $ip_whois_response = whoisip_query($userIP);
    if ($ip_whois_response) {
        print {$log_fh} "Running whois on IP address '", $userIP, "':\n\n";

        foreach ( sort keys( %{$ip_whois_response} ) ) {
            print {$log_fh} "$_ $ip_whois_response->{$_} \n";
        }
    }
    else {
        print {$log_fh} qq|Cannot run whois to do an IP lookup, because no response received when invoking whoisip_query method of Perl module Net::Whois::IP on IP '$userIP'\n\n|;
    }

    close $log_fh or warn "WARNING: Some trouble closing file handle for '$location_of_some_log_file': $!";
}