Need help with perl script with a while loop reading file

Shell Programming and Scripting
1

Good morning, I appreciate any assistance that I can get from the monks out there. I am able to get this to work for me so that I can do a hostname lookup if I only specify one hostname in the script. What I want to do is have a file with hostnames and do lookups for each name in the file. Here is the code that works, and the output:

#!/usr/bin/perl
use strict;
use warnings;

use Net::DNS::Resolver;

my $hostname = 'perlmonks.org';
my $res = Net::DNS::Resolver->new(
  nameservers => [qw(8.8.8.8)],
);

my $query = $res->search($hostname);

if ($query) {
  foreach my $rr ($query->answer) {
    next unless $rr->type eq "A";
    print "Found an A record for $hostname: ".$rr->address;
    print "\n";
  }
}

This is the output you get when you run it:

Found an A record for perlmonks.org: 66.39.54.27
Found an A record for perlmonks.org: 216.92.34.251
Found an A record for perlmonks.org: 209.197.123.153

So now taking it a step further, I want to check a whole file of names. This is the code I have, but it's not working. Can someone please help and let me know where I went wrong?

#!/usr/bin/perl
use strict;
use warnings;

use Net::DNS::Resolver;

open FILE, "<hostname_check.txt" || die $!;
while (<FILE>) {
my $res = Net::DNS::Resolver->new(
  nameservers => [qw(8.8.8.8)],
);
my $query = $res->search($_);

if ($query) {
  foreach my $rr ($query->answer) {
    next unless $rr->type eq "A";
    print "Found an A record for $_: ".$rr->address;
    print "\n";
  }
}
}
close FILE;

---------- Post updated at 08:25 AM ---------- Previous update was at 08:01 AM ----------

I found the mistake.

Here is the updated code that works:


#!/usr/bin/perl
use strict;
use warnings;

use Net::DNS::Resolver;

my $res = Net::DNS::Resolver->new(
  nameservers => [qw(8.8.8.8)],
);

open FILE, "<hostname_check.txt" || die $!;
while (<FILE>) {
chomp;
my $hostname = $_;
my $query = $res->search($hostname);

if ($query) {
  foreach my $rr ($query->answer) {
    next unless $rr->type eq "A";
    print "Found an A record for $_: ".$rr->address;
    print "\n";
  }
}
}
close FILE;

Here is the sample output:

2

Sightly off topic,

Even you you provide a non existence file, die would not be executed and you might screw up your time to troubleshoot the problem. The reason is "||" will return true or every non-empty string you provide as filename.

Always use or instead of || to avoid this.

If you do want to use || , supply the parenthesis to open call.

open (FILE, "<hostname_check.txt") || die $!;

or

open FILE, "<hostname_check.txt" or die $!;

In general, using parenthesis is always a good practice.