open(RESULTS2, "ping.txt") || die;
@results = <RESULTS2>;
open(RESULTS, ">ping.txt") || die;
$j = 1;
$a = 0; $f = 0;
while (@results) {
  print $_;
  if (m/Reply/) {
    $output[$j] = $baseIP.$j.": Alive\n";
    $j++; $a++;
  } elsif (m/Request/) {
    $output[$j] = $baseIP.$j.": Dead\n";
    $j++; $f++;
  } else {
    #@output[$j] = $baseIP.$j.": Unusual Results, requires Manual Ping
+\n";
  }
}

print RESULTS "Pinger Results:\n\n";
print RESULTS "Alive Nodes: $a\n";
print RESULTS "Dead Nodes: $f\n";
print RESULTS "\n\nDetailed Results:\n";
print RESULTS @output;
close(RESULTS);
close(RESULTS2);
[download]

you're getting that warning (and an infinite loop also) because you're using "while" instead of "foreach".

while only automatically sets $_ in the following case:

while (<FILE>)
[download]

otherwise, it does not.