This is a simple script that I run on my raspberry-pi to update my public WAN IPv4 at tunnerbroker.net. Most of the script is configurable so you might use it for other providers with low effort.

update_tunnelbroker.rb

#!/usr/bin/env ruby
require 'net/http'
require 'net/https'

BASEDIR = '/etc'
LAST_IP_FILE = "#{BASEDIR}/tunnelbroker.lastip"

# for debugging.
BE_VERBOSE = false

# point your browser to http://ipv4.tunnelbroker.net/ipv4_end.php for more detailed information
tunnel_options = {
  ip: 'auto', # use auto here, do not use any response from ifconfig.me or similar services for security reasons
  pass: 'echo -n YOURPASSWORD | md5sum',
  apikey: 'YOUR API KEY, FIND IT ON THE MAIN PAGE OF YOUR TB ACCOUNT',
  tid: 000000 # your tunnel id as int
}
# Enpoint to update the tunnel ip. This must be called via https!
tunnel_url = 'ipv4.tunnelbroker.net'
tunnel_path = '/ipv4_end.php'

# Check external ip via this service.
# If you want to change this, you must ensure that only the ip is returned from that
# endpoint. e.g. "123.123.123.123\n"
check_ip_host = 'ifconfig.me'
check_ip_path = '/ip'

# Set fake ip for comparison
ip = "127.0.0.1"

# check for actual file
$stdout.puts "Checking for existing last-ip-file at #{LAST_IP_FILE}" if BE_VERBOSE
if File.exist? LAST_IP_FILE
  last_ip_file = File.open(LAST_IP_FILE, 'r')
  ip = last_ip_file.lines.first.chomp
  $stdout.puts "Found one with IP: #{ip}" if BE_VERBOSE
  last_ip_file.close
end
$stdout.puts "Checking WAN IP" if BE_VERBOSE
external_ip = Net::HTTP.get(check_ip_host, check_ip_path).chomp
$stdout.puts "#{check_ip_host} tells us #{external_ip} as WAN IPv4" if BE_VERBOSE

if ip == external_ip
  $stdout.puts 'IPs are equal, nothing to do. Exiting.' if BE_VERBOSE
  exit 0
end

# Save the last ip in a file
$stdout.puts "Writing new IP to file" if BE_VERBOSE
last_ip_file = File.open(LAST_IP_FILE, 'w')
last_ip_file << external_ip
last_ip_file.close

# Do not reuse the external ip here. this could lead to a security flaw.
# If you do not understand why, please do not change this anyway.
$stdout.puts "Requesting tunnel endpoint to update your WAN IP" if BE_VERBOSE
uri = URI.parse("https://#{tunnel_url}#{tunnel_path}")
uri.query = URI.encode_www_form(tunnel_options)
http = Net::HTTP.new(uri.host, uri.port)
http.use_ssl = true
request = Net::HTTP::Get.new(uri.request_uri)
update_response = http.request(request)

unless update_response.is_a?(Net::HTTPSuccess)
  $stderr.puts "Request unsuccessful", update_response
  exit 1
end

update_result = update_response.body.chomp
$stdout.puts "Recieved [#{update_result}]" if BE_VERBOSE
$stderr.puts update_result if update_result.match /^-ERROR:/