Trigger an exec upon changes to a semi-managed file

monitor_exec.pp

$subject = '/etc/sysconfig/authconfig'
$monitor = '/var/tmp/authconfig_monitor'

file { $subject:
  ensure => file,
}

exec { "trigger on update to $subject":
  provider => shell,
  command  => "date > $monitor && /bin/dostuff",
  onlyif   => "[ ! -e $monitor -o $subject -nt $monitor ]",
  require  => File[$subject],
}