use strict;
use warnings;

my $filepath = "ip.txt";
my $outfile  = "output.txt";

open (HOSTLIST, "$filepath") || die "ERROR: opening $filepath\n";
my @hosts = <HOSTLIST>;
close HOSTLIST;

open (OUTFILE, ">> $outfile") || die "ERROR: opening $outfile\n";

foreach my $host(@hosts)
{
   my $results = `nslookup $host`;
   chomp ($host);
   print OUTFILE "Results for $host:\n";
   print OUTFILE "$results\n\n";
}

close OUTFILE;