How do I specify host as a variable in ansible?

There are examples on the internet but none of them seem to work for me:

test.yaml

---

- hosts: "{{ non_default_host }}"
  tasks:
    - debug:
        msg: 'This is the host specified"

then I run this with

ansible-playbook -i hosts test.yaml -e "non_default_host=<somehost>"

All I see is bunch of warnings:

[WARNING]: No inventory was parsed, only implicit localhost is available
[WARNING]: provided host list is empty, only localhost is available
[WARNING]: Could not match supplied host pattern, ignoring somehost

PLAY [somehost]
skipping: no hosts matched

But if I change the hosts to all

test.yaml

---

- hosts: all
  tasks:
    - debug:
        msg: 'This is the host specified"

and then below command this works fine

   ansible-playbook -i 'somehost,'  test.yaml

Solution

For an inventory file example with content of

[example:children]
default
non_default

[default]
node[01:03].example.com

[non_default]
node[01:03].example.net

checked with

ansible-inventory --inventory example --graph
@all:
  |--@ungrouped:
  |--@example:
  |  |--@default:
  |  |  |--node01.example.com
  |  |  |--node02.example.com
  |  |  |--node03.example.com
  |  |--@non_default:
  |  |  |--node01.example.net
  |  |  |--node02.example.net
  |  |  |--node03.example.net

a minimal example playbook

---
- hosts: "{{ host }}"
  become: false
  gather_facts: false
  connection: local

  tasks:

  - debug:
      msg: "This is the 'hosts: {{ host }}' specified"

called via

 ansible-playbook --inventory example test.yml --extra-vars="host=node03.example.com"

will result into an output of

PLAY [node03.example.com] **********************************

TASK [debug] ***********************************************
ok: [node03.example.com] =>
  msg: 'This is the ''hosts: node03.example.com'' specified'

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