Invoke command only on file change

Question

In Puppet I need to trigger an action if a file resource is changed. I know I can define an execresource for the action, and notify that from the file resoure:

file { '/path/to/myfile':
  content => template("${module_name}/mytemplate.erb"),
  notify  => Exec['my action'],
}

exec { 'my action':
  command   => '...',
  logoutput => true,
}

However, if I do the above, Puppet tries to always apply the exec resource, not just on file changes. How do I ensure that the action is only triggered when the file is modified?

Answer 1

Add the parameter refreshonly to your exec resource and set it to true:

exec { 'my action':
  command     => '...',
  refreshonly => true,
  logoutput   => true,
}

From the documentation:

Refresh: exec resources can respond to refresh events (via notify, subscribe, or the ~> arrow). The refresh behavior of execs is non-standard, and can be affected by the refresh and refreshonly attributes:

• If refreshonly is set to true, the exec runs only when it receives an event. This is the most reliable way to use refresh with execs.