How to test that a registered variable is not empty?

问题

How can I test that stderr is non empty::

- name: Check script
  shell: . {{ venv_name }}/bin/activate && myscritp.py
  args:
    chdir: "{{ home }}"
  sudo_user: "{{ user }}"
  register: test_myscript

- debug: msg='myscritp is Ok'
  when: not test_myscript.stderr

So if there is no error I could read::

  TASK: [deploy | debug msg='critp is Ok] *******
  ok: [vagrant] => {
      "msg": "myscritp is Ok"
  }

In case the stderr is not empty a FATAl error occurs.

回答1:

You can check for empty string (when stderr is empty)

- name: Check script
  shell: . {{ venv_name }}/bin/activate && myscritp.py
  args:
    chdir: "{{ home }}"
  sudo_user: "{{ user }}"
  register: test_myscript

- debug: msg='myscritp is Ok'
  when: test_myscript.stderr == ""

If you want to check for fail:

- debug: msg='myscritp has error: {{test_myscript.stderr}}'
  when: test_myscript.stderr != ""

Also look at this stackoverflow question

回答2:

See ansible-lint default rules. The condition below causes E602 Don’t compare to empty string

    when: test_myscript.stderr != ""

Correct syntax and also "Ansible Galaxy Warning-Free" option is

    when: test_myscript.stderr | length > 0

Update 1. Test bare variable

Quoting from Current rule says:

Use when: var rather than when: var != "" (or ' 'conversely when: not var rather than ``when: var == ""`

For example

    - debug:
        msg: "Empty string '{{ var }}' evaluates to False"
      when: not var
      vars:
        var: ''

    - debug:
        msg: "Empty list {{ var }} evaluates to False"
      when: not var
      vars:
        var: []

give

    "msg": "Empty string '' evaluates to False"
    "msg": "Empty list [] evaluates to False"

Update 2. Remove bare var handling from conditionals

See Ansible 2.8 Release notes

Since Ansible 2.8 bare variables don't work in conditionals anymore. For example

    - debug:
        msg: "The string '{{ my_var }}' evaluates to True"
      when: my_var
      vars:
        my_var: 'abcde'

gives

fatal: [localhost]: FAILED! => {"msg": "The conditional check 'my_var' failed. The error was: error while evaluating conditional (my_var): 'abcde' is undefined

See CONDITIONAL_BARE_VARS

$ ansible-config dump | grep BARE
CONDITIONAL_BARE_VARS(default) = True

回答3:

when: myvar | default('', true) | trim != ''

I use | trim != '' to check if a variable has an empty value or not. I also always add the | default(..., true) check to catch when myvar is undefined too.

来源：https://stackoverflow.com/questions/36912726/how-to-test-that-a-registered-variable-is-not-empty

标签

ansible

YAML