Issue

I'm trying to insert an output of Linux shell to a variable, but for some reason, the variable always empty.

Here is the Ansible code:

  - name: Check PHP version
    shell: php -v 2> /dev/null | awk '{print $2; exit}'
    register: php_version

  - debug: var=php_version

And here is the output:

ok: [10.0.0.5] => {
    "php_version": {
        "changed": true, 
        "cmd": "php -v 2> /dev/null | awk '{print $2; exit}'", 
        "delta": "0:00:00.015180", 
        "end": "2017-01-08 18:41:00.323773", 
        "rc": 0, 
        "start": "2017-01-08 18:41:00.308593", 
        "stderr": "", 
        "stdout": "", 
        "stdout_lines": [], 
        "warnings": []
    }
}

When i run the command directly on the server, i get a valid result:

php -v 2> /dev/null | awk '{print $2; exit}'
7.0.14

What could be the issue?

Solution

As to possible reasons, why you can run the command from CLI, but not Ansible, most likely the path to the php executable is not defined in the PATH variable when you run shell through a non-interactive SSH session^* (as Ansible does).

Use a full path instead of just php in the shell module argument.

What could be the issue?

As you are using a pipeline in the shell call, the return code will be that of the last command (awk) and although the first one fails, you won't be notified.

Awk does not get any input to process and it quits gracefully, and because you are redirecting stderr to /dev/null you don't see any error from the php command.

For example if you explicitly run a non-existent command:

- name: Check PHP version
    shell: qwerty -v 2> /dev/null | awk '{print $2; exit}'
    register: php_version

- debug: var=php_version

you will also get:

"rc": 0,
"start": "2017-01-09 06:35:10.588258",
"stderr": "",
"stdout": "",
"stdout_lines": [],
"warnings": []

^* See the Difference between Login Shell and Non-Login Shell? question on Unix.SE.

Answered By - techraf

Answer Checked By - Dawn Plyler (WPSolving Volunteer)

Friday, July 22, 2022

[SOLVED] Ansible: shell script output always empty

Issue

Solution