#!/usr/local/bin/perl

# Change this to the location of your krb5.conf file
my $krb = "/my/dir/krb5.conf";

use LWP;
use File::Copy;

# address that tells you your IP address
my $url = "http://www.myipaddress.com";;
# get a new agent
my $agent   = LWP::UserAgent->new;
# format request
my $request = HTTP::Request->new(GET => $url);
# get web page
my $response = $agent->request($request);
# check results
$response->is_success or die "$url: ", $response->message,"\n";
# parce answer
@parts = split /\n/, $response->content; 
$ipaddress = "";
foreach $_ (@parts) {
    if (/(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/) {
        warn "Found MULTIPLE copies of IP address.  Probably not good\n"
            if ($ipaddress);
        $ipaddress = $1;
        warn "Found IP address $ipaddress\n";
    }
}

die "Couldn't find your IP address.  Sorry\n" unless ($ipaddress);

# copy old file to .bak
copy ($krb, "$krb.bak");
open (SOURCE, "$krb.bak") or die;
open (TARGET, ">$krb") or die;

while (<SOURCE>) {
    # update proxy_gateway line
    if (/^\s+proxy_gateway/i) {
        print TARGET "        proxy_gateway = $ipaddress\n";
    } else {
        print TARGET;
    }
    print TARGET;
}