How to access a programmatically constructed ansible variable?

Question

I have constructed an ansible variable using two other defined ansible variables. The constructed variable is defined in the vars/main.yml and I want to access the defined value in vars/main.yml. vars/main.yml

---
var1_var2: "some value"

Now, I construct the variable

---
- name: Construct and get the value
  hosts: localhost
  tasks:
  - include_vars: "vars/main.yml"
  - set_fact:
      variable1: "var1"
      variable2: "var2"
  - set_fact:
      final_variable: "{{ variable1 }}_{{ variable2 }}"

  - set_fact: 
      ultimate_variable: "{{ final_variable }}"

If I run the playbook with -vvv flag, I can see that ultimate_variable sets to var1_var2 while I want to get the value defined in the vars/main.yml i.e., some value

TASK [set_fact] 

ok: [localhost] => {
"ansible_facts": {
    "variable1": "var1",
    "variable2": "var2"
},
"changed": false,
"failed": false
}

TASK [set_fact] task path: /home/ubuntu/test.yml:78

ok: [localhost] => {
"ansible_facts": {
    "final_variable": "var1_var2"
},
"changed": false,
"failed": false
}

TASK [set_fact] 

ok: [localhost] => {
"ansible_facts": {
    "ultimate_variable": "var1_var2"
},
"changed": false,
"failed": false
}

Answer 1

updated answer:

use the lookup plugin to do the double replacement:

ultimate_variable: "{{ lookup('vars', '{{final_variable}}') }}"

playbook:

  - include_vars: "vars/main.yml"

  - set_fact:
      variable1: "var1"
      variable2: "var2"
  - set_fact:
      final_variable: "{{ variable1 }}_{{ variable2 }}"

  - set_fact: 
      ultimate_variable: "{{ lookup('vars', '{{final_variable}}') }}"

  - debug:
      var: ultimate_variable

output:

PLAY [localhost] ****************************************************************************************************************************************************************************************************

TASK [include_vars] *************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [set_fact] *****************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [set_fact] *****************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [set_fact] *****************************************************************************************************************************************************************************************************
ok: [localhost]

TASK [debug] ********************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "ultimate_variable": "some value"
}

PLAY RECAP **********************************************************************************************************************************************************************************************************
localhost                  : ok=5    changed=0    unreachable=0    failed=0

hope it helps.