Check the defined variable is empty or not in Ansible - ansible

Question

- hosts: localhost
vars:
files_list:
#it may contain the file_list like
#file_list:
# - "file*"
tasks:
- name: copy
copy:
src: "{{item}}"
dest: "/tmp/"
with_fileglob: "{{files_list}}"
when: files != None
I want to copy some multiple files with a specific pattern from the files_list. but sometimes the file_list may be empty. so how to check if the file_list is empty I have tried above code but it doesn't work. it is giving me following error
The full traceback is:<br>
Traceback (most recent call last):<br>
File "/usr/lib/python2.7/site-packages/ansible/executor/task_executor.py", line 104, in run<br>
items = self._get_loop_items()<br>
File "/usr/lib/python2.7/site-packages/ansible/executor/task_executor.py", line 245, in _get_loop_items<br>
items = wrap_var(mylookup.run(terms=loop_terms, variables=self._job_vars, wantlist=True))<br>
File "/usr/lib/python2.7/site-packages/ansible/plugins/lookup/fileglob.py", line 60, in run<br>
term_file = os.path.basename(term)<br>
File "/usr/lib64/python2.7/posixpath.py", line 121, in basename<br>
i = p.rfind('/') + 1<br>
AttributeError: 'NoneType' object has no attribute 'rfind'<br>
fatal: [machine1.kirusa.com]: FAILED! => {<br>
"msg": "Unexpected failure during module execution.", <br>
"stdout": ""<br>
}
Can you also explain whats this mean.
thank you in advance.

Answer 1

Q: "Check whether the defined variable is empty or not in Ansible."
A: Simply test the variable. An empty list evaluates to False. This also covers the case when the variable is not defined. YAML None is Python null. None also evaluates to False. For example
- debug:
msg: The variable files is an empty list or None.
when: not files|default(None)
In the loop, it's not necessary to test whether the list is empty or not. An empty list will be skipped anyway.
YAML string is a list of characters. An empty string evaluates to False the same way as an empty list does.
Notes
The evaluation of 'not item' works in the context of this question if the variable is a string, list, dictionary, or None. if the variable is a boolean or number this test does not work. See the self-explaining test below
- debug:
msg: "{{ not item }}"
loop:
- ''
- []
- {}
-
- null
- true
- false
- 1
- 0
gives
TASK [debug] **************************************************
ok: [localhost] => (item=) =>
msg: true
ok: [localhost] => (item=[]) =>
msg: true
ok: [localhost] => (item={}) =>
msg: true
ok: [localhost] => (item=None) =>
msg: true
ok: [localhost] => (item=None) =>
msg: true
ok: [localhost] => (item=True) =>
msg: false
ok: [localhost] => (item=False) =>
msg: true
ok: [localhost] => (item=1) =>
msg: false
ok: [localhost] => (item=0) =>
msg: true
To fix this problem test the variable is iterable
- debug:
msg: "{{ item is iterable }}"
loop:
- ''
- []
- {}
-
- null
- false
- 0
gives
TASK [debug] ******************************************************
ok: [localhost] => (item=) =>
msg: true
ok: [localhost] => (item=[]) =>
msg: true
ok: [localhost] => (item={}) =>
msg: true
ok: [localhost] => (item=None) =>
msg: false
ok: [localhost] => (item=None) =>
msg: false
ok: [localhost] => (item=False) =>
msg: false
ok: [localhost] => (item=0) =>
msg: false
Complete test: The variable is empty or None
- debug:
msg: The variable is empty or None.
when:
- not item
- item is iterable or item is none
loop:
- ''
- []
- {}
-
- null
- true
- false
- 1
- 0
gives
TASK [debug] ***************************************************
ok: [localhost] => (item=) =>
msg: The variable is empty or None.
ok: [localhost] => (item=[]) =>
msg: The variable is empty or None.
ok: [localhost] => (item={}) =>
msg: The variable is empty or None.
ok: [localhost] => (item=None) =>
msg: The variable is empty or None.
ok: [localhost] => (item=None) =>
msg: The variable is empty or None.
skipping: [localhost] => (item=True)
skipping: [localhost] => (item=False)
skipping: [localhost] => (item=1)
skipping: [localhost] => (item=0)
A dictionary is also iterable. A list of the keys is used
- debug:
var: item
loop: "{{ files|list }}"
vars:
files:
a: 1
b: 2
c: 3
gives
TASK [debug] ********************************************************
ok: [localhost] => (item=a) =>
ansible_loop_var: item
item: a
ok: [localhost] => (item=b) =>
ansible_loop_var: item
item: b
ok: [localhost] => (item=c) =>
ansible_loop_var: item
item: c

Answer 2

To check if it is empty you need to give as below
when: not files_list
See Default rules here: https://docs.ansible.com/ansible-lint/rules/default_rules.html
It states: Don’t compare to empty string, use when: var rather than when: var != "" (or conversely when: not var rather than when: var == "")

Answer 3

You can first assert that it is indeed a list and then assert that it has more than one element:
when: (files_list is defined) and (files_list | type_debug == 'list') and (files_list | count > 0)