# Variables in host\_vars possible? **URL:** \ **Category:** Get Help\ **Tags:** playbook\ **Created:** [October 7, 2024, 10:29am UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740 "2024-10-07T10:29:30Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![starflighter](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/starflighter/32/4992_2.png) [@starflighter](https://forum.ansible.com/u/starflighter)\ **Post date:** [October 7, 2024, 10:29am UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/1 "2024-10-07T10:29:30Z")
Hi all, we use lists for vlans in our host\_vars files. Is it possible to reuse variables definded further up in the file? For example like this: ```auto vlans: - 34 - 356 - 22 reuse_vlans: vlans add_vlans: - vlans - 666 ``` I have trouble to get this working. Maybe you can help me? Thanks, starflighter Ansible-Version: ansible 2.10.6 (we are stuck at python version 3.6.15) ---
**Author:** ![dnmvisser](https://avatars.discourse-cdn.com/v4/letter/d/8e8cbc/32.png) [@dnmvisser](https://forum.ansible.com/u/dnmvisser)\ **Post date:** [October 7, 2024, 11:14am UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/2 "2024-10-07T11:14:25Z")
[https://docs.ansible.com/ansible/latest/collections/ansible/builtin/union\_filter.html](https://docs.ansible.com/ansible/latest/collections/ansible/builtin/union_filter.html) ---
**Author:** ![starflighter](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/starflighter/32/4992_2.png) [@starflighter](https://forum.ansible.com/u/starflighter)\ **Post date:** [October 7, 2024, 12:14pm UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/3 "2024-10-07T12:14:56Z")
@dnmvisser Do you have an example how to use the filter in a host\_vars file? That would be great 🙂 I can’t make it work. The filter is just printed out as string. content of host\_vars file: ```auto vlans: - 34 - 356 - 22 reuse_vlans: vlans add_vlans: "{{ vlan | union('666') }}" ``` Output of ansible-inventory --host xxx ```auto { "add_vlans": "{{ vlan | union('666') }}", "ansible_host": "xxx",, "reuse_vlans": "vlans", "vlans": [ 34, 356, 22 ] } ``` ---
**Author:** ![jiholland](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/jiholland/32/11273_2.png) [@jiholland](https://forum.ansible.com/u/jiholland)\ **Post date:** [October 7, 2024, 12:24pm UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/4 "2024-10-07T12:24:57Z")
```yaml --- vlans: - 34 - 356 - 22 add_vlans: - 666 all_vlans: "{{ vlans | union(add_vlans) }}" ``` ---
**Author:** ![starflighter](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/starflighter/32/4992_2.png) [@starflighter](https://forum.ansible.com/u/starflighter)\ **Post date:** [October 7, 2024, 12:53pm UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/5 "2024-10-07T12:53:46Z")
Hi @jiholland, I copied your example to host\_vars/r1-xxx. And the result from ansible-inventory --host r1-xxx is: ```auto { "add_vlans": [ 666 ], "all_vlans": "{{ vlans | union(add_vlans) }}", "ansible_host": "xxx", "vlans": [ 34, 356, 22 ] } ``` So the filter is not executed, do you have any Idea? Thanks, starflighter ---
**Author:** ![jiholland](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/jiholland/32/11273_2.png) [@jiholland](https://forum.ansible.com/u/jiholland)\ **Post date:** [October 7, 2024, 1:14pm UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/6 "2024-10-07T13:14:46Z")
You need to use it in a playbook. ```yaml - name: Print all_vlans. ansible.builtin.debug: var: all_vlans ``` ---
**Author:** ![bvitnik](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/bvitnik/32/4132_2.png) [@bvitnik](https://forum.ansible.com/u/bvitnik)\ **Post date:** [October 7, 2024, 9:10pm UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/7 "2024-10-07T21:10:23Z")
Just a note that lists can be concatenated in Jinja scripts using `+` operator so this is also valid: ```auto --- vlans: - 34 - 356 - 22 add_vlans: - 666 all_vlans: "{{ vlans + add_vlans }}" ``` Unlike with `union`, list element ordering is preserved in this case. ---
**Author:** ![bcoca](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/bcoca/32/9269_2.png) [@bcoca](https://forum.ansible.com/u/bcoca)\ **Post date:** [October 7, 2024, 9:27pm UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/8 "2024-10-07T21:27:30Z")
didn’t see anyone show the ‘reuse’, so here it is ```auto reuse_vlans: '{{vlans}}' ``` ---
**Author:** ![utoddl](https://sea1.discourse-cdn.com/ansible/user_avatar/forum.ansible.com/utoddl/32/249_2.png) [@utoddl](https://forum.ansible.com/u/utoddl)\ **Post date:** [October 8, 2024, 12:31am UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/9 "2024-10-08T00:31:34Z")
You can also do it at the YAML level — no Ansible involved! ```yaml --- vlans: &vlans - 34 - 356 - 22 reuse_vlans: *vlans add_vlans: - *vlans - 666 ``` Bonus: It uses the same syntax as C pointers, because _that’s_ never lead to mistakes. 🙂 You can read about [Anchors and Aliases](https://yaml.org/spec/1.2.2/#3222-anchors-and-aliases) in the YAML 1.2 spec, or [google it](https://www.google.com/search?q=yaml+anchors+aliases) for comprehensible explanations. The spec _says it_, but it doesn’t actually _tell you anything_ unless you already know what it means. Classic spec! Don’t get me wrong: it’s a good spec, but it’s not a tutorial. Note: “`add_vlans`” above results in a two-element list. The first element is the three-element `vlans` list, and the second element is “`666`”. Here’s the playbook with a little cheating. ```yaml # starflighter-01.yml - name: Variables in host_vars possible hosts: localhost gather_facts: false vars: vlans: &vlans - 34 - 356 - 22 reuse_vlans: *vlans add_vlans: - *vlans - 666 tasks: - name: Show vlans ansible.builtin.debug: msg: - '{{ vlans }}' - '{{ reuse_vlans }}' - '{{ add_vlans | flatten }}' # <-- I cheated! ``` which produces ```txt TASK [Show vlans] **** ok: [localhost] => msg: - - 34 - 356 - 22 - - 34 - 356 - 22 - - 34 - 356 - 22 - 666 ``` ---
**Author:** ![system](https://us1.discourse-cdn.com/ansible/original/1X/1882d9a01da5d8996a862359b0913cc568a39b84.svg) [@system](https://forum.ansible.com/u/system)\ **Post date:** [November 7, 2024, 12:31am UTC](https://forum.ansible.com/t/variables-in-host-vars-possible/9740/10 "2024-11-07T00:31:55Z")
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