deferred evaluation (?)

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1

I’m trying to loop over a set of strings with ansible.builtin.debug, and I want to produce a three-part message for each string, like this:

  • name: Demo expressions
    ansible.builtin.debug:
    msg:
  • ‘{{ item }}’
  • ‘evaluate item as a Jinja2 expression’
  • ‘like previous, but with “| bool” appended’
    loop:
  • “0”
  • “1”
  • “2”
  • “[‘aa’, ‘bb’, ‘cc’] | intersect([‘bb’, ‘cc’])”
  • “[‘aa’, ‘bb’, ‘cc’] | intersect([‘bb’, ‘cc’]) | length > 0”

The first part of the message should show the string, and it does.
The second part somehow needs to show the result of evaluating the string as a Jinja2 expression.
The third part is supposed to append “| bool” onto the string, evaluate that as a Jinja2 expression, and show the result.

I feel like there should be some way to do this with lookup(‘items’,…), but I’m having no luck. I’d appreciate any suggestions. Thanks,

2

try the template lookup

3

I’m confused. The template lookup wants a [list of] file[s]. I’d rather not write these strings out to temp files just to get them templated. Or am I misinterpreting your suggestion?

4

post expected result

5

Sure. Here’s a complete example where the debug task’s output msg contains exactly what I want. However, instead of each item being a 3-element list of strings, I want to pass in a single string, and use that string in various ways within the msg: expressions to accomplish the same thing.

To be clear: as presented below, this problem isn’t worth solving. After all, there’s the playbook down below already! But that’s not the point. The point is to understand effective run-time techniques to build strings containing Jinja2 expressions and have them evaluated. (“Templated” I guess is the verb rather than “evaluated,” but that feels backwards. In my brain, “to template” means to examine a sufficiently large set of outputs and create a template adequate to reproduce those outputs from reasonable inputs. But I digress.)

Apparently it’s possible to write such strings to a file and use lookup(‘template’,tmpfilename), but there doesn’t seem to be the equivalent of lookup(‘template’,jinja2_expression_string). Not that I have found anyway.

[utoddl@tango ansible]$ **cat deferred.yml** 
---
# deferred.yml
- name: Deferred evaluation demo
  hosts: localhost
  gather_facts: false
  tasks:
    - name: Evaluate booleanness of various expressions
      ansible.builtin.debug:
        msg:
          - '{{ item.0 }}'
          - '{{ item.1 }}'
          - '{{ item.2 }}'
      loop:
        - [   "0",
           "{{ 0 }}",
           "{{ 0 | bool }}"]
        - [   "1",
           "{{ 1 }}",
           "{{ 1 | bool }}"]
        - [   "2",
           "{{ 2 }}",
           "{{ 2 | bool }}"]
        - [   "['aa', 'bb', 'cc'] | intersect(['bb', 'cc'])",
           "{{ ['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) }}",
           "{{ ['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) | bool }}"]
        - [   "['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) | length > 0",
           "{{ ['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) | length > 0 }}",
           "{{ ['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) | length > 0 | bool }}"]
[utoddl@tango ansible]$ **ansible-playbook deferred.yml**

PLAY [Deferred evaluation demo] *************************************************************************

TASK [Evaluate booleanness of various expressions] ******************************************************
ok: [localhost] => (item=['0', '0', False]) => {
    "msg": [
        "0",
        "0",
        false
    ]
}
ok: [localhost] => (item=['1', '1', True]) => {
    "msg": [
        "1",
        "1",
        true
    ]
}
ok: [localhost] => (item=['2', '2', False]) => {
    "msg": [
        "2",
        "2",
        false
    ]
}
ok: [localhost] => (item=["['aa', 'bb', 'cc'] | intersect(['bb', 'cc'])", ['bb', 'cc'], False]) => {
    "msg": [
        "['aa', 'bb', 'cc'] | intersect(['bb', 'cc'])",
        [
            "bb",
            "cc"
        ],
        false
    ]
}
ok: [localhost] => (item=["['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) | length > 0", True, True]) => {
    "msg": [
        "['aa', 'bb', 'cc'] | intersect(['bb', 'cc']) | length > 0",
        true,
        true
    ]
}

PLAY RECAP **********************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0
6

Create a template. For example,

cat create_test.j2

{% for i in strings %}
{{ i }} = {{ '{{' }} {{ i }} {{ '}}' }}
{% endfor %}

Then, the below playbook

cat pb.yml

- hosts: localhost
  tasks:
    - template:
        src: create_test.j2
        dest: /tmp/test.j2
      vars:
        strings:
          - '0'
          - '1'
          - "['aa', 'bb', 'cc']|intersect(['bb', 'cc'])"
          - "['aa', 'bb', 'cc']|intersect(['bb', 'cc'])|length > 0"
    - debug:
        msg: "{{ lookup('template', '/tmp/test.j2') }}"

gives abridged

  msg: |-
    0 = 0
    1 = 1
    ['aa', 'bb', 'cc']|intersect(['bb', 'cc']) = ['bb', 'cc']
    ['aa', 'bb', 'cc']|intersect(['bb', 'cc'])|length > 0 = True