Welcome to the Monastery, mattp341!

What's happening is you're receiving an undefined/null value from inet_aton() when you mistype a hostname, and that's what inet_ntoa() is complaining about.

You should check the return from inet_aton() before sending it into inet_ntoa(). Here's a very rough example. It'll ask the user for a hostname until inet_aton() returns something useful:

my $addr;

while (! $addr){
    print "enter a damned FQDN: ";
    my $input = <STDIN>;
    chomp $input;

    $addr = inet_aton($input);
}

my $ip = inet_ntoa($addr);
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You could also just terminate the application if a hostname is mistyped instead of looping and re-asking for input:

my $addr = inet_aton($input);

die "invalid hostname specified\n" if ! $addr;

my $ip = inet_ntoa($addr);

...
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