How to write dynamic variable in Ansible playbook

Question

Based on extra vars parameter I Need to write variable value in ansible playbook

ansible-playbook playbook.yml -e "param1=value1 param2=value2 param3=value3"

If only param1 passed

myvariable: 'param1'  

If only param1,param2 passed

myvariable: 'param1,param2' 

If param1,param2,param3 are passed then variable value will be

myvariable: 'param1,param2,param3' 

When I try to create variable dynamically through template then my playbook always takes previous variable value. But inside dest=roles/myrole/vars/main.yml its writing correct value.

What I make a try here

- hosts: local
  user: roop
  gather_facts: yes
  connection: local

  tasks: 

  - template: src=roles/myrole/templates/myvar.j2 dest=roles/myrole/vars/main.yml

  - debug: var=myvariable

  roles:
        - { role: myrole }

So inside myrole directory I have created template and vars

- roles
  - myrole
    - vars/main.yml
    - templates/myvar.j2 

templates/myvar.j2

{% if param1 is defined and param2 is defined and param3 is defined %}
  myvariable: 'param1,param2,param3'
{% elif param1 is defined and param2 is defined %}
  myvariable: 'param1,param2'
{% elif param1 is defined %}
  myvariable: 'param1'
{% else %}
  myvariable: 'default-param'
{% endif %} 

As I know if only two condition then I can do this using inline expression like below

{{ 'param1,param2' if param1 is defined and param2 is defined else 'default-param' }}

<do something> if <something is true> else <do something else>

Is it possible if - elif - else in inline expression like above. Or any other way to assign value dynamically in ansible playbook?

Answer 1

I am sure there is a smarter way for doing what you want but this should work:

- name         : Test var
  hosts        : all
  gather_facts : no
  vars:
    myvariable : false
  tasks:
    - name: param1
      set_fact:
        myvariable: "{{param1}}"
      when: param1 is defined

    - name: param2
      set_fact:
        myvariable: "{{ param2 if not myvariable else myvariable + ',' + param2 }}"
      when: param2 is defined

    - name: param3
      set_fact:
        myvariable: "{{ param3 if not myvariable else myvariable + ',' + param3 }}"
      when: param3 is defined

    - name: default
      set_fact:
        myvariable: "default"
      when: not myvariable

    - debug:
       var=myvariable

Hope that helps. I am not sure if you can construct variables dynamically and do this in an iterator. But you could also write a small python code or any other language and plug it into ansible

Answer 2

my_var: the variable declared

VAR: the variable, whose value is to be checked

param_1, param_2: values of the variable VAR

value_1, value_2, value_3: the values to be assigned to my_var according to the values of my_var

my_var: "{{ 'value_1' if VAR == 'param_1' else 'value_2' if VAR == 'param_2' else 'value_3' }}"

Answer 3

I would first suggest that you step back and look at organizing your plays to not require such complexity, but if you really really do, use the following:

   vars:
    myvariable: "{{[param1|default(''), param2|default(''), param3|default('')]|join(',')}}"