How to create a 'null' default in Ansible

Question

I want 'lucy' to follow the user module creators' default behaviour which is to create and use a group matching the user name 'lucy'. However for 'frank' I want the primary group to be an existing one; gid 1003. So my hash looks like this:

lucy:
  comment: dog
frank:
  comment: cat
  group: 1003

And my task looks like this:

- name: Set up local unix user accounts
  user:
    name: "{{ item.key }}"
    comment: "{{ item.value.comment }}"
    group: "{{ item.value.group | default(undef) }}"
  loop: "{{ users|dict2items }}"

This doesn't work, as undef is not recognised. Nor is anything else I can think of. 'null', 'None' etc. all fail. '' creates an empty string which is not right either. I can't find out how to do it. Any ideas?

Answer 1

default(omit) is what you are looking for. For example,

- name: Set up local Unix user accounts
  user:
    name: "{{ item.key }}"
    comment: "{{ item.value.comment }}"
    group: "{{ item.value.group | default(omit) }}"
  loop: "{{ users|dict2items }}"

---

Comments

Comment by Lucas Basquerotto: "... omit only works correctly when used directly in a module, it won't work in a set_fact ..."

A: You're wrong. For example, default(omit) works both in set_fact and in the module. The first item in the list defaults to false with the result "VARIABLE IS NOT DEFINED!". The second item defaults to omit. Omitted parameter get_checksum defaults to true with the checksum in the results

shell> cat pb.yml
- hosts: localhost
  tasks:
    - set_fact:
        test:
          - "{{ gchk|default(false) }}"
          - "{{ gchk|default(omit) }}"
    - stat:
        path: /etc/passwd
        get_checksum: "{{ item }}"
      loop: "{{ test }}"
      register: result
    - debug:
        var: item.stat.checksum
      loop: "{{ result.results }}"

gives

shell> ansible-playbook pb.yml | grep item.stat.checksum
  item.stat.checksum: VARIABLE IS NOT DEFINED!
  item.stat.checksum: 7c73e9f589ca1f0a1372aa4cd6944feec459c4a8

In addition to this, default(omit) works as expected also in some expressions. For example

    - debug:
        msg: "{{ {'a': item}|combine({'b': true}) }}"
      loop: "{{ test }}"

gives

  msg:
    a: false
    b: true

  msg:
    b: true

See the results without default values

shell> ansible-playbook pb.yml -e "gchk={{ true|bool }}"