How to test that a registered variable is not empty?
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
(ansible 2.9.6 ansible-lint 4.2.0)
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
Quoting from source code
"Use
when: var|length > 0
rather thanwhen: var != ""
(or ' 'converselywhen: var|length == 0
rather thanwhen: var == ""
)"
Notes
- Test empty bare variable e.g.
- 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"
- But, testing non-empty bare variable string depends on CONDITIONAL_BARE_VARS. Setting
ANSIBLE_CONDITIONAL_BARE_VARS=false
the condition works fine but settingANSIBLE_CONDITIONAL_BARE_VARS=true
the condition will fail
- debug:
msg: "String '{{ var }}' evaluates to True"
when: var
vars:
var: 'abc'
gives
fatal: [localhost]: FAILED! =>
msg: |-
The conditional check 'var' failed. The error was: error while
evaluating conditional (var): 'abc' is undefined
Explicit cast to Boolean prevents the error but evaluates to False i.e. will be always skipped (unless var='True'
). When the filter bool
is used the options ANSIBLE_CONDITIONAL_BARE_VARS=true
and ANSIBLE_CONDITIONAL_BARE_VARS=false
have no effect
- debug:
msg: "String '{{ var }}' evaluates to True"
when: var|bool
vars:
var: 'abc'
gives
skipping: [localhost]
- Quoting from Porting guide 2.8 Bare variables in conditionals
- include_tasks: teardown.yml
when: teardown
- include_tasks: provision.yml
when: not teardown
" based on a variable you define as a string (with quotation marks around it):"
In Ansible 2.7 and earlier, the two conditions above evaluated as True and False respectively if teardown: 'true'
In Ansible 2.7 and earlier, both conditions evaluated as False if teardown: 'false'
In Ansible 2.8 and later, you have the option of disabling conditional bare variables, so when: teardown always evaluates as True and when: not teardown always evaluates as False when teardown is a non-empty string (including 'true' or 'false')
- Quoting from CONDITIONAL_BARE_VARS
"Expect that this setting eventually will be deprecated after 2.12"
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.