Unable to get the list value returned by the json query from the ansible facts - ansible

Question

I am trying to get the size_available value for the /home filesystem from the ansible facts.
I am using the following code after setting gather_facts: True
{{ansible_facts['mounts']|json_query('[?mount==`/home`].size_available')}}
This way I get something like this [34545646] with msg: from the debug module.
I need to compare this value to a static one and continue or not the playbook but when I try:
{{ansible_facts['mounts']|json_query('[?mount==`/home`].size_available')[0]}}
I get:
"msg": "template error while templating string: expected token 'end of print statement', got '['. String: > {{ansible_facts['mounts']|json_query('[?mount==`/home`].size_available')[0]}}
Even if the type_debug shows me the result should be indeed a list that should be accessible by the [0] extension.

Answer 1

You need to parenthesize the initial expression before attempting to index the result, like this:
{{
(
ansible_facts['mounts'] |
json_query('[?mount==`/home`].size_available')
)[0]
}}
E.g., if I run this playbook on my system:
- hosts: localhost
gather_facts: true
tasks:
- debug:
msg: >-
{{
(
ansible_facts['mounts'] |
json_query('[?mount==`/home`].size_available')
)[0]
}}
I get this output for the debug task:
TASK [debug] ********************************************************************************************
ok: [localhost] => {
"msg": "402658955264"
}

Answer 2

Q: "Get the size_available value for a mount point from the ansible facts."
A: Declare the dictionary below, for example in group_vars
shell> cat group_vars/all/mount_vars.yml
mount_size_available: "{{ ansible_mounts|
items2dict(key_name='mount',
value_name='size_available') }}"
gives, for example
mount_size_available:
/: 8480206848
/boot/efi: 30278656
/export: 12902629376
Then, you can easily reference an available size at a mount point, for example
mount_size_available['/export']: '12902629376'
Example of a project for testing
shell> tree .
.
├── ansible.cfg
├── group_vars
│   └── all
│   └── mount_vars.yml
├── hosts
└── pb.yml
2 directories, 4 files
shell> cat ansible.cfg
[defaults]
gathering = explicit
inventory = $PWD/hosts
remote_tmp = ~/.ansible/tmp
retry_files_enabled = false
stdout_callback = yaml
shell> cat group_vars/all/mount_vars.yml
mount_size_available: "{{ ansible_mounts|
items2dict(key_name='mount',
value_name='size_available') }}"
size_1G: "{{ 1 * 1024 * 1024 * 1024 }}"
size_10G: "{{ 10 * 1024 * 1024 * 1024 }}"
size_100G: "{{ 100 * 1024 * 1024 * 1024 }}"
shell> cat hosts
localhost
shell> cat pb.yml
- hosts: localhost
tasks:
- setup:
gather_subset: mounts
- debug:
var: mount_size_available
- debug:
var: mount_size_available['/export']
- debug:
msg: "Free space at /export is greater than 10G."
when: mount_size_available['/export'] > size_10G|int
- debug:
msg: "Free space at /export is less than 100G."
when: mount_size_available['/export'] < size_100G|int
gives
shell> ansible-playbook pb.yml
PLAY [localhost] *****************************************************************************
TASK [setup] *********************************************************************************
ok: [localhost]
TASK [debug] *********************************************************************************
ok: [localhost] =>
mount_size_available:
/: 8479465472
/boot/efi: 30278656
/export: 12901998592
TASK [debug] *********************************************************************************
ok: [localhost] =>
mount_size_available['/export']: '12901998592'
TASK [debug] *********************************************************************************
ok: [localhost] =>
msg: Free space at /export is greater than 10G.
TASK [debug] *********************************************************************************
ok: [localhost] =>
msg: Free space at /export is less than 100G.
PLAY RECAP ***********************************************************************************
localhost: ok=5 changed=0 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0