Ansible and `changed_when` based on `stdout` value

Question

I am running a custom command because I haven't found a working module doing what I need, and I want to adjust the changed flag to reflect the actual behaviour:

- name: Remove unused images   shell: '[ -n "$(docker images -q -f dangling=true)" ] && docker rmi $(docker images -q -f dangling=true) || echo Ignoring failure...'   register: command_result   changed_when: "command_result.stdout == 'Ignoring failure...'"  - debug: var="1 {{ command_result.stdout }}"   when: "command_result.stdout != 'Ignoring failure...'" - debug: var="2 {{ command_result.stdout }}"   when: "command_result.stdout == 'Ignoring failure...'" 

(I know the shell command is ugly and could be improved by a more complex script but I don't want to for now)

Running this task on an host where no Docker image can be removed gives the following output:

TASK: [utils.dockercleaner | Remove unused images] ****************************  changed: [cloud-host] => {"changed": true, "cmd": "[ -n \"$(docker images -q -f dangling=true)\" ] && docker rmi $(docker images -q -f dangling=true) || echo Ignoring failure...", "delta": "0:00:00.064451", "end": "2015-07-30 18:37:25.620135", "rc": 0, "start": "2015-07-30 18:37:25.555684", "stderr": "", "stdout": "Ignoring failure...", "stdout_lines": ["Ignoring failure..."], "warnings": []}  TASK: [utils.dockercleaner | debug var="DIFFERENT {{ command_result.stdout }}"] ***  skipping: [cloud-host]  TASK: [utils.dockercleaner | debug var="EQUAL {{ command_result.stdout }}"] ***  ok: [cloud-host] => {     "var": {         "EQUAL Ignoring failure...": "EQUAL Ignoring failure..."     } } 

So, I have this stdout return value "stdout": "Ignoring failure...", and the debug task shows the strings are equal, so why is the task still displayed as "changed"?

I am using ansible 1.9.1.

The documentation I am refering to is this one: http://docs.ansible.com/ansible/playbooks_error_handling.html#overriding-the-changed-result

Answer 1

I think you may have misinterpreted what changed_when does.

changed_when marks the task as changed based on the evaluation of the conditional statement which in your case is:

"command_result.stdout == 'Ignoring failure...'"

So whenever this condition is true, the task will be marked as changed.