features of register:

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1

Hello,

The feature

  • name: capture output
    debug: msg=“hello world”
    register: myvar
    allows to capture the result of the task inside the variable myvar.

if a with_item is added, myvar.results becomes a list with all the results

I have a few questions regarding this :

1/ register and role variables

is it possible to register inside myvar only a subpart of the result, like

register: myvar filter=subkey

2/ variable expansion

is it possible to name a variable by variable

vars:

  • varname: myvar

tasks:

  • name: register into variable myvar
    debug: msg=“hello world”
    register: “{{ varname }}”

I have tried some things but cannot make them work

thank you

2

  1. No, you must name a top level variable with register and cannot add to an existing variable.

  2. Maybe you should try it and let us know :slight_smile: … However, a major goal of Ansible is readability and auditability, so I don’t think you should probably do that in most cases unless you’ve got a really good use case for it - it would probably make your playbooks much less transparent.

3

regarding “variable expansion” it does not work currently I think (except if my test is wrong):

  • hosts: localhost
    gather_facts: no
    vars:
  • varname: myvar
    tasks:
  • name: register into myvar
    tags: expansion
    debug: msg=“hello world”
    register: “{{ varname }}”
  • name: output myvar
    tags: expansion
    debug: var=myvar

PLAY [localhost] **************************************************************

TASK: [register into myvar] ***************************************************
ok: [127.0.0.1] => {
“msg”: “hello world”
}

TASK: [output myvar] **********************************************************
ok: [127.0.0.1] => {
“myvar”: “{{ myvar }}”
}

note that if i do

debug: var={{myvar}}

I get
fatal: [127.0.0.1] => One or more undefined variables: ‘myvar’ is undefined

so it does not work currently. I can think of some use cases where it could be handy to have such expansions.

the main case I see “pro” expansion is the following :

1/ register: foo inside a role
2/ call the role 2 times with different parameters
you lost one of the 2 results.

it’s like programming
my_important_result = role(params1)
my_important_result = role(params2)

but I agree with you variable expansion is probably dangerous for readability.

Jerome

4

Wrong:

register: “{{ varname }}”

Correct:

register: varname