Use of uninitialized value $domain in string ne at dnsdig.cgi line 9.
Use of uninitialized value $domain in concatenation (.) or string at dnsdig.cgi line 18.
Can't call method "answer" on an undefined value at dnsdig.cgi line 19.

##</code><code>##

#!/usr/bin/perl -w

use strict;
use Net::DNS;
my $dns = new Net::DNS::Resolver;

my $domain;

if($domain ne "") {
print "<form action=\"dnsdig.cgi\" method=\"post\">
<input name=\"domain\" type=\"text\" value=\"\" />
<input type=\"submit\" value=\"Get MX\" />
</form>";
} else {
    my $mx = $dns->query( $domain, 'MX' );

print "content-type:text/html; charset=utf-8\n\n";
    print "$domain:\n\n";
    foreach my $rr ($mx->answer) {
        print "<br />", $rr->exchange, ' [<b>', $rr->preference, "</b>]\n";
    }
}