Ansible Demo: Compare

README.md

Ansible Compare

Frequently we might need to make a change to a file and respond to removals as well as additions.

This playbook demonstrates how we can detect changes (using the Ansible host).

1. Run the playbook in regular mode ansible-playbook demo-compare.yaml. Look for a file named demo-compare.txt alongside the playbook.
2. Change a name in the file_data list.
3. Re-run the playbook in --check mode.
4. If any changes would be made (--check mode) or are made (regular mode) as a result, these are displayed by the final debug module.

Output (snippet)

TASK [debug] ******************************************************************
ok: [127.0.0.1] => {
      "msg": "removed: []\nadded: ['rudolph']\n"
}

demo-compare.yaml

---
- hosts: 127.0.0.1
  vars:
    file_data:
      - dasher
      - dancer
      - prancer
      - vixen
      - comet
      - cupid
      - donder
      # - rudolph

  tasks:

    - name: create a file with one name per line
      copy:
        dest: "{{ hostvars[inventory_hostname].playbook_dir }}/demo-compare.txt"
        content: |
          {% for thing in file_data %}{{ thing }}
          {% endfor %}
      diff: yes
      register: file_result

    - debug:
        var: file_result

    - when: file_result.changed
      block:
        - name: split the before and after variables into lines
          set_fact:
            file_lines_before: "{{ file_result.diff[0].before.split() }}"
            file_lines_after: "{{ file_result.diff[0].after.split() }}"

        - name: difference the lines both ways round
          set_fact:
            file_lines_removed: "{{ file_lines_before | difference(file_lines_after) }}"
            file_lines_added: "{{ file_lines_after | difference(file_lines_before) }}"

        - debug:
            msg: |
              removed: {{ file_lines_removed }}
              added: {{ file_lines_added }}