#type 'perl scansub.pl' for help
#
#This program scans a C-class subnet and prints the results to corresponding text file.
#If a computer has once answered the ping, it will not be added to the list again.
#To sort the output type 'perl scansub.pl sort <textfile>'

use strict;
use Net::Ping;

my $host;
my $subnet;
my %state;
my $h;
my $time;
my $if;
my $of;
my $line;

if ($ARGV[0] eq 'sort'){
	&sort;
	exit;
}

unless ($subnet=$ARGV[0]){
	&usage;
	exit;
}
open OF,">>$subnet\.txt";


for $h(1 .. 255){
	$host="$subnet\.$h";
	$state{$host}=''
}


while(){
open OF,">>$subnet\.txt";
for $h(1 .. 254){
	#sleep 2;
	$host="$subnet\.$h";
	my $p=Net::Ping->new('icmp');
	print "\nPinging host $host";
	if ($p->ping($host,1)){
		print " alive";
		if ($state{$host} ne 'up'){
			$time=localtime();
			print OF "$host\twas up at $time\n";
			$state{$host}='up';
		}
	
	}
   }
close OF;
sleep 600
}

sub usage{
	print"
This program scans a C-class subnet 
and lists all machines, that have answered ping,
in a text file.
Use this program to sort the output.

Usage:		perl scansub.pl <subnet>
Example:	perl scansub.pl 192.168.0

Sort:		perl scansub.pl sort <file>
Example:	perl scansub.pl sort 192.168.0.txt

";
}

sub sort{
	unless ($if=$ARGV[1]){
		&usage;
		exit;
	}
open IF,"$if" or die "Cannot open file $if for read: $!";
$of=">s.$if";
open OF,$of;

my @data=<IF>;
my @sorted=grep {s/(^|\D)0+(\d)/$1$2/g,1} sort
    grep {s/(\d+)/sprintf"%06.6d",$1/ge,1} @data;

foreach $line(@sorted){
	print OF $line;
}
close IF;
close OF;

exit;
}