The lookup plugin is always executed on the control node (that's your Ansible server), which is to say that the lookup plugin does not do something on your managed nodes (the target systems).

To use the pipe plugin, the Python pipe.py script must be in your Ansible plugins lookup directory, such as /usr/lib/python3.12/site-packages/ansible/plugins/lookup/pipe.py.

The env or printenv command will display certain global variables, something like this.

[john.doe@server1 ~]$ env
HOSTNAME=server1
SHELL=/bin/bash
USER=john.doe

The lookup plugin can be used to get the value of the global variables. For example, to display the value of the HOSTNAME global variable

---
- hosts: localhost
  tasks:
  - name: return control node hostname
    ansible.builtin.debug:
      msg: "{{ lookup('ansible.builtin.pipe', 'hostname') }}"
...

Running this playbook should return something like this. In this example, server1 is the hostname of the control node.

TASK [return control node hostname]
ok: [server1.example.com] => {
    "msg: "server1"
}