How to check if a process is running in Ruby

running = !(Process.getpgid(pid) rescue nil).nil?

pid_file = "#{shared_dir}/tmp/pids/http_proxy_server.pid"
if File.exist?(pid_file)
    pid = IO.readlines(pid_file).first.chomp
    running = !(Process.getpgid(pid) rescue nil).nil?
    log_message = running ? "Iniciando proceso #{pid}\nEscuchando en puerto #{port}..." : "Process #{pid} not running"
else
    log_message = "pid file for http_proxy_server not found"
end
puts log_message