Changing apache user and group in /etc/apache2/envvars using sed in a puppet exec. Stolen from https://github.com/Intracto/Puppet/blob/master/apache2/manifests/init.pp#L12-L26

example.pp

exec { "sed -i 's/www-data/vagrant/g' /etc/apache2/envvars":
  onlyif => "/bin/grep -c 'www-data' /etc/apache2/envvars",
  notify => Service['apache2'],
  require => Package['apache2'],
}