Ok R. Below,I am trying to modify and add comment in my code

#!/usr/bin/perl  -w
use String::Util 'trim';

=head1 NAME

ping_linux.pl - This script works on Linux system  pings a host and re
+turns statistics data.

=head1 VERSION

Version 1.0

=head1 AUTHOR

Gaurav Dubey (gaurav.d@ronankiinfotech.com

=head1 SYNOPSIS

  ./ping_linux.pl [-c --> count (Number of echo requests to be sent)] 
+[-i --> interval (Interval in milliseconds between echo  requests)] [
+-s --> packetsize (Size of icmp packet)] [-h --> destinationIP (Ip ad
+dress of destination host)] [-w --> AllowableTime (Max time in second
+s for sending receiving echo requests/reponse)]"

=head1 DESCRIPTION

This pings a host via the system ping command and returns RTA ,Tx pack
+ets,Rx packets,TTL,Packet-loss

=cut

use strict;

use Getopt::Long;
use Pod::Usage;

my ($host,$count,$interval,$packetsize,$allowableTime);
GetOptions(
    "h|host=s",    \$host,
    "c|count=i",    \$count,
    "i|interval=i",     \$interval,
    "s|packetsize=i", \$packetsize,
    "w|allowableTime=i",\$allowableTime,
);

#pod2usage("$0: No host given!\n") unless($host);
pod2usage("$0:No host given!\n") unless($host && $host =~ /^((([2][5][
+0-5]|([2][0-4]|[1][0-9]|[0-9])?[0-9])\.){3})([2][5][0-5]|([2][0-4]|[1
+][0-9]|[0-9])?[0-9])$/);
$count = 5 unless ($count);
$interval = 1 unless ($interval);
$packetsize = 56 unless ($packetsize);
$allowableTime = 1 unless ($allowableTime);

#Here I am opening a ping process on linux system .
open CMD, "/bin/ping -c $count -i $interval -s $packetsize -w $allowab
+leTime $host |" or die "Can't open ping: $!";

#This code has been working fine by executing "./ping_linux.pl -h 192.
+168.1.150 -c 1" from terminal.And I want to mention it that this host
+ is up and running with in our network.
my (@values1,@val1,@values2,@val2,@values3,@values4,@values5); 
 while (<CMD>) {
#In below, if-block I am extracting the host-ip,Packet Size,Packet+Hea
+der Size from the output line 
#PING 192.168.1.150 (192.168.1.150) 56(84) bytes of data

        if ( $_ =~ /PING/ ){
           @values1 = split ;
          @val1 = split(/\(/,$values1[3]); 
         $val1[1] =~ s/\)//;
           }  
#Below if-block has been used to extract the TTL values from the line 
+"64 bytes from 192.168.1.150: icmp_req=1 ttl=254 time=4.43 ms"
#which is 254
    
      if ($. == 2) {
        @values2 = split;
          @val2 = split(/\=/ , $values2[5]);
           }
#in this if-block I am extracting the transfer-recieved packets and pa
+cket loss ,from the output line "3 packets transmitted, 3 received, 0
+% packet loss, time 2003ms"
      if ($_ =~ /packets/) {
          #print "$_ ";
         @values3 = split;
          }
#In last if-block I am extracting the rtt avg/max/min/med values ,from
+ the output-line "rtt min/avg/max/mdev = 2.113/2.895/4.434/1.089 ms"
      if ($_ =~ /^rtt/) {
           #print "$_ ";
        @values4 = split /\=/;
         @values5 = split(/\// ,$values4[1]);
        }
   }



#print "$values1[1] \n";
 #   print "$val1[0] \n";
 #print "$val1[1] \n";
#print "$val2[1] \n";
#print "$values3[0] \n";
#print "$values3[3] \n";
#print "$values3[5] \n";
#print "$values4[1]";
#my $min = trim($values5[0]); 
#print "$min\n";
#print "$values5[1] \n";
#print "$values5[2] \n";
#print "$values5[3] ";

close CMD
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So its working fine

Now when I passed an IP which is not present in our company network say

 ping 192.168.1.10 -c 1
PING 192.168.1.10 (192.168.1.10) 56(84) bytes of data.

--- 192.168.1.10 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms
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So How can I relay a message by using perl that host is not present in our network?

But if it's present in our company's network but system is down.Say,

#ping 192.168.1.25  -c 1
PING 192.168.1.25 (192.168.1.25) 56(84) bytes of data.
From 192.168.1.23 icmp_seq=1 Destination Host Unreachable

--- 192.168.1.25 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0
+ms
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for this I have to say system is down.Remember here one thing that I am using this perl script on Fedora-14 Redhat Linux System

You really need to use some helpful names for your variables. I started to work on your code and gave up because while I have a good idea what this means:

print "$hostname\n";
print "$ip\n";
print "$pkt_size\n";
print "$ttl\n";
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it will take me some time to work out what this means:

#print "$values1[1] \n";
#   print "$val1[0] \n";
#print "$val1[1] \n";
#print "$val2[1] \n";
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I would suggest, other than using sane variable names, that you alter your series of if statements to use the if/elsif/else construct. This will give you a way to catch the error conditions from your ping.

On a more minor point, it looks like you only allow a restricted range of IP addresses for your $host value. Yet later you capture the IP used by ping. Is there a case where you ask it to ping n.n.n.n and it pings m.m.m.m? If not you can just use the IP you fed into it.

Cheers,
R.

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