#!/usr/bin/perl -w
use strict;

my $first;
my $ip;

# use the address from @ARGV if it exists or request from STDIN
if (@ARGV) {
	$ip = shift @ARGV;		
} else { 
	print "Enter an ip address: ";
	chomp( my $ip = <STDIN> );
}


# split the ip address into subnets and store in an array
my @subnets = split(/\./, $ip);
# ensure the ip address is valid. 
sanitize(@subnets);


for (0..$#subnets) {
	# take each subnet and generate the hex out of the subnet divided by 16 
	# then the remainder
	my $pair = hexize((int($subnets[$_]/16)),($subnets[$_]%16));
	print $pair;
}
print "\n";

sub sanitize {
	# takes a subnet and makes sure that its not over 255,
	# greater than 0 and that there are 4 subnets. 
	foreach $_ (@_) {
		if ($_ > 255) {
			print "illegal ip address\n";
			exit;
		} elsif ($_ < 0) {
			print "illegal ip address\n";
			exit;
		} elsif ($#_ != 3) {
			print "illegal ip address\n";
			exit;
		}
	}
}
sub hexize {
	# Takes two values 
	# 1: the subnet divided by 16 
	# 2: the subnet divided by 16's remainder
	# Then it applies the right letter if applicable
	my @unit;
	foreach $_ (@_) {
		if ($_ == 10) {
			push @unit,"A";
		} elsif ($_ == 11) {
                	push @unit,"B";
        	} elsif ($_ == 12) {
                	push @unit,"C";
        	} elsif ($_ == 13) {
                	push @unit,"D";
        	} elsif ($_ == 14) {
                	push @unit,"E";
        	} elsif ($_ == 15) {
                	push @unit,"F";
        	} else {
			push @unit,$_;
		}
	}
	return "$unit[0]$unit[1]";
}