Ansible tasks to set (aka register) a variable, based on stdout of a shell command

gistfile1.yml

- name: get gridfs host ip from name (required for nginx gridfs module)
  shell: 'ping -q -c 1 -t 1 {{ gridfs_host }} | grep PING | sed -e "s/).*//" | sed -e "s/.*(//"'
  register: gridfs_ip_command
  when: gridfs_ip is not defined

- name: set gridfs ip
  set_fact: gridfs_ip={{ gridfs_ip_command.stdout }}
  when: gridfs_ip is not defined