mattp341 has asked for the wisdom of the Perl Monks concerning the following question:

I am brand spanking new to Perl and this is my first script ever, please go easy on me. So this is my code here: 

 
#Author: Matt Pawlaczyk
#Date:   1-6-2017
#Desc:   This script takes in a URL and continuosly pings it. The IP e
+quivalent of the hostname is returned
#        and a message displays to indicate if it is online or not.

use strict;
use warnings;
use 5.010;
use Socket;
use Net::Ping;
#acquire a host to ping from the user
   print "Enter a website to ping:\n";
   my $input = <STDIN>;
   chomp $input;
#get the IP address for the hostname   
   my $address = inet_ntoa(inet_aton($input));
#a ping object is created, the protocol by default is TCP, changed to 
+icmp
   my $p = Net::Ping->new("icmp");
#ping the inputted website to see if it is live or not. (we do this 10
+ times)  
   print "Attempting to ping $input.....\n";
   for(my $i = 1; $i <= 10; $i = $i++){
      if ($p->ping($input))
      {
         print "Response from $address succesful\n";
         #delay execution by 1 second
         sleep(1);
      }
      else
      {
         return undef;
          print "No response from server, try again.\n";
      }
   }
   print "Done.";

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When I enter in for example, "google.com" It works, the ping is successful and I get the IP for the hostname - life is good. However, when I enter in an invalid URL, I get an error message that I am having trouble making sense of. It says to me: 
Use of uninitialized value in subroutine entry at pingTest.pl line 16,
+ <STDIN> line 1.
Bad arg length for Socket::inet_ntoa, length is 0, should be 4 at ping
+Test.pl line 16, <STDIN> line 1.

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Can anybody help me? I've been searching for about an hour now and cannot come up with an answer to this problem.

Replies are listed 'Best First'.
Re: Getting what I seem to believe are error with inet_ntoa(inet_aton())
by stevieb (Canon) on Jan 06, 2017 at 20:46 UTC

    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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      Thanks so much I got it working!

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