Rendering environment variables in an Ansible shell command - ansible

Question

I'm trying to run a shell command on a remote host using Ansible, and this command must also include a local environment variable.
While the variable is correctly set, the output is not the one I'd expect and I don't understand why.
This is a sample playbook that I prepared for this case:
---
- name: "Ansible local variable in shell command"
hosts: localhost
vars:
variable: "{{ lookup('env', 'VARIABLE') }}"
connection: local
tasks:
- name: "Prints the local variable"
shell: "echo {{ vars.variable }}"
register: "output"
- debug: var=output.stdout_lines
If running VARIABLE=random ansible-playbook playbook.yml I would expect it to print random, what I get instead is this error:
fatal: [localhost]: FAILED! => {"changed": true, "cmd": "echo {{ lookup('env', 'VARIABLE') }}", "delta": "0:00:00.004725", "end": "2023-02-17 21:56:21.282225", "msg": "non-zero return code", "rc": 2, "start": "2023-02-17 21:56:21.277500", "stderr": "/bin/sh: -c: line 1: syntax error near unexpected token `('\n/bin/sh: -c: line 1: `echo {{ lookup('env', 'VARIABLE') }}'", "stderr_lines": ["/bin/sh: -c: line 1: syntax error near unexpected token `('", "/bin/sh: -c: line 1: `echo {{ lookup('env', 'VARIABLE') }}'"], "stdout": "", "stdout_lines": []}
The most relevant part is the content of stderr, where we can see this one:
"/bin/sh: -c: line 1: syntax error near unexpected token `('\n/bin/sh: -c: line 1: `echo {{ lookup('env', 'VARIABLE') }}'
From my understanding, this means that vars.variable has been considered as a plain string instead of being rendered with the result of the lookup function.
But why does this happen? What am I missing on this one?

Answer 1

You must not use vars.variable (which contains the raw Jinja2 string as seen in your error message) but simply variable as demonstrated in the following fixed example:
---
- name: "Ansible local variable in shell command"
hosts: localhost
vars:
variable: "{{ lookup('env', 'VARIABLE') }}"
connection: local
tasks:
- name: "Prints the local variable"
#shell: "echo {{ vars.variable }}"
shell: "echo {{ variable }}"
register: "output"
- debug: var=output.stdout_lines
works fine for me:
$ VARIABLE="Hello, world" ansible-playbook playbook2.yml
PLAY [Ansible local variable in shell command] *******************************************************************************************************************************************************************************************************************************
TASK [Gathering Facts] *******************************************************************************************************************************************************************************************************************************************************
ok: [localhost]
TASK [Prints the local variable] *********************************************************************************************************************************************************************************************************************************************
changed: [localhost]
TASK [debug] *****************************************************************************************************************************************************************************************************************************************************************
ok: [localhost] => {
"output.stdout_lines": [
"Hello, world"
]
}
PLAY RECAP *******************************************************************************************************************************************************************************************************************************************************************
localhost : ok=3 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0