I keep saying time and time again that Ansible is not a programming language, it’s similar to one, it can do some programming things but ultimately it’s messy and I hate it BUT I can make it do some strange things.
List manipulation being one of those.

In this example I have two directories that I want to compare, directory one (/tmp/1) and directory two (/tmp/2). Directory one is the Source, that I want directory two to look like.

The use case is I want to sync /tmp/1 to /tmp/2 but you only want to remove the files in that are no longer /tmp/1, then you can sync (copy/template) the /tmp/1 directory knowing that nothing exists /tmp/2 that shouldn’t be there.

The ansible code is this with debug statements:

- hosts: local
  become: false
  tasks:

    - name: find 1
      find: path=/tmp/1
      register: one
    - debug: msg="{{ one }}"

    - name: find 2
      find: path=/tmp/2
      register: two

    - debug: msg="{{ item.path }}"
      with_items:
        - "{{ two.files }}"

    - set_fact:
        one_list: []
        two_list: []
        new_list: []

    - name: append
      set_fact: one_list="{{ one_list }} + [ '{{ item.path | basename }}' ]"
      with_items:
        - "{{ one.files }}"

    - name: append
      set_fact: two_list="{{ two_list }} + [ '{{ item.path | basename }}' ]"
      with_items:
        - "{{ two.files }}"

    - debug: msg="{{ one_list }}"
    - debug: msg="{{ two_list }}"

    - set_fact: new_list="{{ two_list | difference(one_list) }}"
    - debug: msg="{{ new_list }}"

The final result is new_list is a list (array) that contains what needs to be removed from /tmp/2 to bring it in line with /tmp/1