Skip a Loop based on a Condition#

Problem#

We want to skip an entire task that contains a loop. If we use when as usual, the loop will still be evaluated, but each task will be skipped. So the following would not work:

skip_loop.yaml

- name: Cleanup Directory
  hosts: web
  vars:
    expected_files:
      - one.txt
      - two.txt
      - picture.jpg
    grass: red
  tasks:
    - name: Clean up files
      ansible.builtin.file:
        path: "{{ item }}"
        state: absent
      loop: "{{ expected_files }}"
      when: grass == "green"

Solution#

We use a condition in line of the template variable to execute the loop with an empty list.

skip_loop.yaml

- name: Cleanup Directory
  hosts: web
  vars:
    expected_files:
      - one.txt
      - two.txt
      - picture.jpg
    grass: red
  tasks:
    - name: Clean up files
      ansible.builtin.file:
        path: "{{ item }}"
        state: absent
      loop: "{{ expected_files if grass == 'green' else [] }}"

Another common use case is to execute a run only if the variable containing the list is defined:

skip_loop.yaml

- name: Cleanup Directory
  hosts: web
  tasks:
    - name: Clean up files
      ansible.builtin.file:
        path: ‘{{ item }}’
        state: absent
      loop: "{{ expected_files | default([]) }}"

Explanation#

If a task contains a loop, when is evaluated for each element in this loop. Think of a loop as just a wrapper to execute the same task multiple times.