Ansible : evaluate variable inside a variable with register

Question

I have a task where i need to evaluate a variable attribute , where the name is already a vaiable.

here is the scenario :

i'm executing a shell command ( docker ps ) and i'm registering the output in a variable , where the name is already dynamic:

- name : Display running containers for {{apiType}}
  shell: docker ps
  register: docker_containers_{{apiType}}
  when:
    - '"containers" in type'

no i want to display the content of that ouput and not only the string itself , so i need to do something like this:

- name: Display running containers for {{apiType}}
  debug:
   msg: {{docker_containers_{{apiType}}.stdout}}
  when:
    - '"containers" in type'

of course , this : {{docker_containers_{{apiType}}.stdout}} is syntaxically refused

i ve tried this : {{docker_containers_[apiType].stdout}}

but it fails.

Suggestions?

Answer 1

This is a FAQ. You can build a string and use that to index the hostvars for your current host:

- name: Display running containers for {{apiType}}
  debug:
   msg: "{{ hostvars[inventory_hostname]['docker_containers_' + apiType].stdout}}"
  when:
    - '"containers" in type'

...this assumes that your docker_containers_... variable is a host fact, rather than, say, something set via group_vars or a vars stanza in your playbook.

Here's a runnable example:

- hosts: localhost
  gather_facts: false
  vars:
    apiType: foo

  tasks:
    - set_fact:
        docker_containers_foo:
          stdout: "this is foo"
    - set_fact:
        docker_containers_bar:
          stdout: "this is bar"

    - name: Display running containers for {{apiType}}
      debug:
        msg: "{{ hostvars[inventory_hostname]['docker_containers_' + apiType].stdout}}"