open(INPUT, $ARGV[0]) || die "Cannot do eet! $!";  	# Takes the input file name on the command line and builds an array.
while (<INPUT>) {									# This is the ARP Cache file created from a copy/paste of a routers 
  push @data, "$_";									# show arp command.
}
close(INPUT);
													
for (@data) {     # This section iterates over the ARP cache array and pulls the IP and MAC address out and stores it into a hash
  if ($_ =~ m/([\d]+\.[\d]+\.[\d]+\.[\d]+).*([\w]{4})\.([\w]{4})\.([\w]{4})/i) {			# Key is MAC 
    my $temp = $2.$3.$4;																	# Value is IP
    $hash{$temp} = $1;
  }
}