How to create an empty file with Ansible?

Question

The documentation of the file module says

If state=file, the file will NOT be created if it does not exist, see the copy or template module if you want that behavior.

So we use the copy module, using force=no to create a new empty file only when the file does not yet exist (if the file exists, its content is preserved).

- name: ensure file exists
  copy:
    content: ""
    dest: /etc/nologin
    force: no
    group: sys
    owner: root
    mode: 0555

This is a declarative and elegant solution.

Something like this (using the stat module first to gather data about it and then filtering using a conditional) should work:

- stat: path=/etc/nologin
  register: p

- name: create fake 'nologin' shell
  file: path=/etc/nologin state=touch owner=root group=sys mode=0555
  when: p.stat.exists is defined and not p.stat.exists

You might alternatively be able to leverage the changed_when functionality.

Another option, using the command module:

- name: Create file
  command: touch /path/to/file
  args:
    creates: /path/to/file

The 'creates' argument ensures that this action is not performed if the file exists.

Building on the accepted answer, if you want the file to be checked for permissions on every run, and these changed accordingly if the file exists, or just create the file if it doesn't exist, you can use the following:

- stat: path=/etc/nologin
  register: p

- name: create fake 'nologin' shell
  file: path=/etc/nologin 
        owner=root
        group=sys
        mode=0555
        state={{ "file" if  p.stat.exists else "touch"}}