Send me an email when a machine becomes pingable

ping-email.rb

#!/usr/bin/env ruby
require 'rubygems'
require 'net/ping'
require 'net/smtp'


server=ARGV.first
smtp_server='mailhost.shef.ac.uk'
from_name="Pingy Test Thingy"
from_address="pingy@yourdomain.com"
to_name="Test User"
to_address="a.j.beresford@sheffield.ac.uk"

message=<<MESSAGE_END
From: #{from_name} <#{from_address}>
To: #{to_name} <#{to_address}>
Subject: #{server} came back

Good News Everybody! #{server} is back with us!
MESSAGE_END

pinger=Net::Ping::ICMP.new server

MISSED_PING_HYSTERESIS_LIMIT=3
SECONDS_BETWEEN_PINGS=5

missed_pings=0
already_alerted=false
loop do 
  if pinger.ping
    puts "ACK: #{server}"
    unless already_alerted
      puts "Sending Mail"
      Net::SMTP.start(smtp_server) { |smtp| smtp.send_message(message, from_address, to_address) }
      already_alerted=true
      missed_pings=0
    end
  else
    puts "NACK: #{server}"
    missed_pings++
    already_alerted=false if missed_pings > MISSED_PING_HYSTERESIS_LIMIT
  end
  sleep SECONDS_BETWEEN_PINGS  
end