#!/usr/bin/perl 

use strict;
use warnings;
use Regexp::Common qw /net/;
use IO::Prompt;

my $ip;

# formatting the input

while ( $ip = prompt "Enter a valid IP address: ", -until => qr/^$RE{net}{IPv4}{-sep=> '.'}$/ )  {
    print "Your say: '$_'\n";
}

# dotted-quad format to hexadecimal
my $hex_ip = unpack "H*", pack "C4", split '\.', $ip;