Tool: checkip.rb

26 Jan 2010

Often I find my self in need of accessing my home network for various reasons but the IP address changes more often than not. So I wrote this little script, that will connect to whatismyip.com and email me if the IP has changed. I also setup a crontab entry that will run the script every hour to look for ip address changes. The code and the crontab are posted below if anyone feels they could use the script. Please let me know if there are any errors or if you need help.

#!/usr/bin/env ruby

#Jacob Hammack
#http://www.hammackj.com
#checkip.rb is a tool to check the internet facing ip and emailing a specific user if the ip changes from the previously noted ip

require 'rubygems'
require 'open-uri'
require 'hpricot' #sudo gem install hpricot
require 'net/smtp'

$FROM_EMAIL = "FROMEMAILADDRESSHERE"
$TO_EMAIL = "TOEMAILADDRESSHERE"

# read_ip () reads the locally stored .checkip file for the last known ip
#
def read_ip()
  ip = ""
  begin
    File.open(".checkip", "r") { |f| ip = f.gets() }
  rescue => err
    #file doesn't exist, can ignore it
  end

  return ip
end

# main() checks the whatismyip.com website for changes in ip address stored locally
#
def main()
  puts "checkip.rb\nJacob Hammack\nhttp://www.hammackj.com\n"

  new_ip = Hpricot(open("http://www.whatismyip.com/automation/n09230945.asp"))
  new_ip = new_ip.html.chomp
  ip = read_ip()
  ip.chomp! unless ip == nil

  if new_ip != ip
    puts "[!] Different IP Address Detected emailing admin!"
    email_admin(new_ip)
    File.open(".checkip", "w") { |f| f.puts new_ip }
  else
    puts "[*] No IP change"
  end
end

# email_admin(ip) sends a email to the $TO_EMAIL variable using a local sendmail mta
#
def email_admin(ip)
  msg = sprintf "From: checkip.rb <%s>\nTo: %s <%s>\nSubject: Your IP has been updated!\nDate: %s\nMessage-Id: <%s@hammackj.net>\n\nYour IP address has changed to %s\n", $FROM_EMAIL, $FROM_EMAIL, $TO_EMAIL, Time.now, ip, ip

  Net::SMTP.start('localhost', 25) do |smtp|
    smtp.send_message msg, $FROM_EMAIL, $TO_EMAIL
  end
end

main()

[hammackj@frijoles:/opt/scripts]# sudo crontab -l
# m h  dom mon dow   command
0 * * * * /usr/bin/ruby /opt/scripts/checkip.rb