Use value of CLI variable as the name of a host_vars variable?

October 8, 2022

Is there a way to use the value of one Ansible variable as the name of another variable so I can extract a value from its list?

host_vars:

this:
  does: walk
  says: hi

that:
  does: run
  says: hello

On the CLI when I run the playbook, I add -e="thing=this".

In the playbook, I’ve tried all manner of things to expand the variable thing to its value this, then use this to extract the value of does in the host_vars file.

Using the variable name directly obviously works:

- name: Check what the thing does
  debug:
    msg: "{{ this['does'] }}"

But the following do not:

{{ thing['does'] }}
{{ {{ thing }}['does'] }}

Those, plus several other iterations I’ve tried all either throw an error or print out the literal string.

>Solution :

You need the vars lookup plugin to indirectly address variables. See

shell> ansible-doc -t lookup vars

For example,

    - debug:
        msg: "{{ lookup('vars', thing).does }}"

should give (abridged)

shell> ansible-playbook pb.yml -e "thing=this"
  ...
  msg: walk

Example of a complete playbook for testing

- hosts: localhost

  vars:

    this:
      does: walk
      says: hi
    that:
      does: run
      says: hello

  tasks:

    - debug:
        msg: "{{ lookup('vars', thing).does }}"