run_once.rb

# Use it by including it directly in the unix-ruby script

def run_script_once
  emails = %w[[email protected]]

  path = "#{$0}.pid"
  if File.exists?(path)
    pid = IO.read(path).to_i
    begin
      if Process.getpgid(pid)
        puts "Already Running!"
        hostname = `/bin/hostname`
        emails.each do |email|
          `/usr/bin/mail -s "WARNING: script #{path} on host #{hostname} already running" "#{email}" < /dev/null`
        end
        exit
      end
    rescue Errno::ESRCH
      puts "** .pid file exists, but process isn't running, continue.. **"
    end
  end
  at_exit {  File.unlink(path) if File.exist?(path) }
  IO.write(path, Process.pid.to_s)
end

run_script_once

run_once_test.rb

#!/usr/bin/env ruby

require "#{__dir__}/run_once"


max = 12
delay = 10
1.upto(max) do |idx|
  puts "#{idx}/#{max} Waiting #{delay} seconds .."
  sleep delay
end