playbook.yml

---
- name: inventory, task variables and facts
  hosts:
    - test

  tasks:
    - name: example task
      command: hostname
      register: hostname_var

    - name: facts can be determined by output of tasks
      set_fact:
        flag_task_a: "{{ hostname_var.stdout }}"
      when: hostname_var.rc == 0

    - debug: var=flag_task_a
    - debug: var=flag_task_b
    - debug: var=flag_user_a
    - debug: var=flag_user_b
    - debug: var=flag_user_c

  vars:
    flag_task_a: "a"
    flag_task_b: "b"
    flag_user_a: "{{ flag_a | default('a') }} "
    flag_user_b: "{{ flag_b | default('b') }} "
    flag_user_c: "{{ flag_c | default('c') }} "