#!/usr/bin/perl
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#!/usr/bin/perl -w
use strict;
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So, with strict enabled, you should declare your $INPUT_FILE variable as a lexical variable, using my:

my $INPUT_FILE = "ipnum";
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open(INPUT_FILE);
@array = ;
close(INPUT_FILE);
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Second, that next line doesn't even compile. You want to read from the filehandle--Perl makes that quite simple.

So we'll replace what you have with this:

open INPUT_FILE, $INPUT_FILE
    or die "Can't open $INPUT_FILE: $!";
my @array = <INPUT_FILE>;
close INPUT_FILE
    or die "Can't close $INPUT_FILE: $!";
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Second, you're looping over "@arrays"--but you never defined "@arrays". You defined "@array". Perhaps this was a typo?

So, with that in mind (and with the name of your loop variable changed to reflect more accurately the value it contains):

for my $address (@array) {
    my $output = `nslookup $address`;
    print $output;
}
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#!/usr/bin/perl -w

use strict;

my $input_file = "ipnum";
my @array;

{
    local *INPUT;
    open(*INPUT, $input_file) or die "Cannot open: $!";
    @array = <INPUT>;
    close(*INPUT) or die "Cannot close: $!";
}

foreach my $address (@array) {
    my $output = `nslookup $address`;
    print $output, "\n";
}
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I'm really not happy with the use of backticks here (at least without sanity checks).
Consider if ipnum looks like this:

192.168.0.1
192.168.0.2 ; rm -rf /
192.168.0.3
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Running with -T gives :

[nobody@archaia scratch]$ ./wibble
Insecure dependency in `` while running with -T switch at ./wibble lin
+e 16.
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Of course, if ipnum can be trusted, then this isn't an issue.

> foreach my $address (@arrays) {

s/@arrays/@array/
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Just in case he copies it verbatim.

my $output=`nslookup $array`;

would have to become:

my $addr=inet_aton($array);
my $output=gethostbyaddr($addr, AF_INET);
$output=$array unless $output;

use Socket;

#!/usr/bin/perl

use strict;

open(INPUT_FILE, "ipnum");
my @array = <INPUT_FILE>;  #this puts each line of ipnum into an array
close(INPUT_FILE);

for my $line (@array) {
  my @output = `nslookup $line`;
  print "@output";
}
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You might want an appropriately placed chomp() in there somewhere if newlines cause you some problems.

Can you elaborate on that, please?

I was curious too, so to resurrect a 12 year old thread with 14 year old info: http://impressive.net/archives/fogo/20001005080818.O15286@impressive.net "Paul Vixie: nslookup's functionality will probably return in some form, since a lot of people seem to like it. The existing BIND8 implementation of nslookup is very closely bound to the internal API of BIND8, which does not exist in BIND9. Generally, "dig NAME RRTYPE" is all most people need to know, but if it's important to direct a query to a particular server then the syntax is "dig NAME RRTYPE @SERVERADDRESS". Lastly, if what you want is a zone transfer (which nslookup implemented in its "ls" command), the syntax is "dig NAME axfr @SERVERADDRESS", in other words, use an RRTYPE of "axfr". "David Conrad: The behavior of nslookup is suboptimal in many areas, giving weird or un-useful error messages, however it is difficult to simply fix nslookup as many people rely on the weird behavior (particularly in scripts). The functionality provided by nslookup will likely continue (given how many people have written scripts that require and are used to using nslookup), but we didn't have time to do the full revision we wanted, so we give a warning suggesting people use dig instead. " 2014 now - still using nslookup. :-)