use strict;
use warnings;

use Fcntl ':flock';
use Parallel::ForkManager;

my $PORT_NO = '80';           # Default port of HTTP
my $SERVICE = "http";
my $pm = new Parallel::ForkManager(20); # At any instant maximum 20 processes can run simultaneously
my $ip;                 # Stores the IP address supplied by user

if(!$ARGV[0]) {
  print "Program intended to check the machines where webserver is running. \n";
  print "USAGE: perl wst.pl [ip(xxx.xxx.xxx)] \nInput only 3 octets\n";
  exit;
}
if($ARGV[0] =~ /^\d{1,3}\.\d{1,3}\.\d{1,3}$/) {
    $ip = $ARGV[0];
} else {
    print "Enter IP in valid format (xxx.xxx.xxx) \n";
    print "USAGE: perl wst.pl [ip(xxx.xxx.xxx)] \n";
    exit;
}

## file to write to
open(my $fh, '+>', "ipaddresses.txt") or die "ack: $!";

foreach my $i (1..254) {
  my $ip_add = sprintf("%s.%s",$ip,$i);
  my $pid = $pm->start and next;
  my $val = `nmap -sT -p $PORT_NO $ip_add | grep $SERVICE`;
  if ($val) {
    my $test = (split(/\s+/,$val))[1];
    if ($test =~ m/open/) {
      flock $fh, LOCK_EX;
      print "$ip_add\n";
      flock $fh, LOCK_UN;
    } 
  } 
  $pm->finish;
} 
print "reaping....might take some time\n";
$pm->wait_all_children;

seek $fh, 0, 0;
print "Web Server is running at : ", <$fh>, "\n";

exit 0;