My brother at one time, long ago in the mid 90's, tried to create a program in Visual Basic without any programming experience... --He threatened to name his next dog, "Subscript Out Of Range." An array always has a size, even if it's empty. When you access array elements by their index number, you are, in less common terms, actually using a "subscript" number. In perl, array index/subscript numbers are positive integers starting at 0 for the first element. If an array is accessed in scalar context, it will return the number of elements in the array. If an array is empty in perl (no elements) and accessed in scalar context, it will return -1, an invalid index/subscript for all arrays. As a perl beginner, you're missing some of the basics, namely always use 'strict' and 'warnings' and while developing, also using 'diagnostics' can be real helpful.

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;    # this makes error messages nicer.
[download]

As for the problem with your code, I'd bet you have a blank line in your input file. You're not checking $_ (default input), so you'd be feeding an empty string into Net::Whois::ARIN.

#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;    # this makes error messages nicer.
use Net::Whois::ARIN;

my $file="file_containing_IPs.txt";

open(LIST,$file) or die "Unable to open file $file:$!\n";

my $w = Net::Whois::ARIN->new(
  host    => 'whois.arin.net',
  port    => 43,
  timeout => 30,
);

while(<LIST>) {
  foreach ($_) {
    chomp;
    if(defined $_ && $_) {
      my @output = $w->network($_);
      foreach my $net (@output) {
        printf(
          "CIDR: %s\tNetName: %s\tNetHandle: %s\n",
          $net->CIDR,
          $net->NetName,
          $net->NetHandle,
        );
      }
    }
  }
}

close(LIST);
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.