In Ansible playbooks how can i set a variable depending on inventory_hostname filtering matching a list of predefined values?

Question

I'm trying to assign a variable in my playbook for later use based on hostname:

(without revealing actual hostnames)

• ...p........001
• ...s........001
• ...t........001
• etc...

and a list to assign depending on the 4th letter from the hostname

• Production
• Staging
• Test
• etc...

based on the 4th letter in the hostname, I want to set myvar per hostname which I run this playbook against:

• if p, myvar = Production
• if s, myvar = Staging
• if t, myvar = Test

I have tried, and decided that the 4th letter can be captured from the hostname as so:

inventory_hostname[3]

This method seems to work:

  - name: Some task
    set_fact:
      **myvar**: Production
    when: inventory_hostname[3] == "p"

  - name: Some task 2
    set_fact:
      **myvar**: Staging
    when: inventory_hostname[3] == "s"

  - name: Some task 3
    set_fact:
      **myvar**: Test
    when: inventory_hostname[3] == "t"

  - name: Content of myvar?
    debug:
      msg: "{{ myvar }}"
    when: myvar is defined

The output is as follows, which appears to work:

TASK [Prod environment?] ********************************************************************************************
ok: [...p........001]
    
TASK [Stage environment?] ********************************************************************************************
skipping: [...p........001]
    
TASK [Test environment?] ********************************************************************************************
skipping: [...p........001]
    
TASK [Content of myvar?] ********************************************************************************************
ok: [...p........001] => {
        "msg": "Production"
    }

I assume the solution might be a single task which literally translates to something like:

- name: Some task
  set_fact:
    **myvar**: if inventory_hostname[3] == p or s or t and this exists in {{ varfile }} set Production or Staging or Test

I want to either:

1. Reduce the number of tasks required to work this variable out by either doing a "loop and replace" based on the 4th character match, but I cant figure out the best way to do this within a playbook.
2. Accept a better solution to this problem.

Answer 1

Create a dictionary myvar_dict, declare myvar and put it into the group_vars

shell> cat group_vars/all/myvar.yml
myvar_dict:
  p: Production
  s: Staging
  t: Test
  default: Sales
myvar: "{{ myvar_dict[inventory_hostname.3]|default(myvar_dict.default) }}"

Given the inventory

shell> cat hosts
001production
001staging
001test
007business

The playbook

- hosts: all
  tasks:
    - debug:
        var: myvar

gives

TASK [debug] ************************************************************************************
ok: [001production] => 
  myvar: Production
ok: [001staging] => 
  myvar: Staging
ok: [001test] => 
  myvar: Test
ok: [007business] => 
  myvar: Sales

---

Create the dictionary from the list

Given the list

  myvar_list: [Production, Staging, Test]

declare the default and create a dictionary

  myvar_default: {default: Sales}
  myvar_dict: "{{ dict(myvar_list|map('first')|map('lower')|
                       zip(myvar_list))|
                  combine(myvar_default) }}"

gives

  myvar_dict:
    default: Sales
    p: Production
    s: Staging
    t: Test

Example of a complete playbook for testing

- hosts: all

  vars:

    myvar_list: [Production, Staging, Test]

    myvar_default: {default: Sales}
    myvar_dict: "{{ dict(myvar_list|map('first')|map('lower')|
                         zip(myvar_list))|
                    combine(myvar_default) }}"

    myvar: "{{ myvar_dict[inventory_hostname.3]|default(myvar_dict.default) }}"

  tasks:

    - debug:
        var: myvar_dict
      run_once: true

    - debug:
        var: myvar