#! /usr/bin/perl
use strict;
use warnings;
use Parallel::ForkManager;

my @arr;
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;
}

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

print "Web Server is running at : @arr \n";

exit 0;