#/usr/local/bin/perl 

# Creates a list of all subnets 
$sn = 0xffff & system("ypcat hosts | cut -f1-3 -d \".\" | sort -u | sort -k 1n,1 
n -k 2n,2n -k 3n,3n -t \".\" -r>subnets.list"); 

# User is prompted to anter an IP address 
open(CHECK, ">check.list") || die "ERROR! This file cannot be created!\n"; 
print "Enter an IP address.\n"; 
$ip = <STDIN>; 
chomp ($ip); 
$partial = rindex($ip, "."); 
$ip_subnet = substr($ip, 0, $partial); 
chomp ($ip_subnet); 
print CHECK "$ip_subnet\n"; # Checkpoint - prints subnet 

# Match entered subnet to active subnet list 
open(SUBNET, "subnets.list") || die "Unable to open file: subnets.list\n"; 
while (<SUBNET> ) { 
if ($ip_subnet eq $subnet) { 
print "PASS\n"; 
} else { 
print "FAIL\n"; 
} 
}