Executing a command in ansible on some hosts from a file

I have a group of hosts in the inventory

[group 1]
host1
host2

[group 2]
host1
host2
host3
host4
host5

hoste1 has a json file with a list of some objects, example:

[ { "hostName": "host2"}, { "hostName": "host4"}]

or maybe one host

[ { "hostName": "host1"}]

I need to read this file from ansible and execute the command only on hosts from this file

Reading the file

- name: Read /tmp/hosts.json
  shell: "/tmp/hosts.json | jq '.[].hostName'"
  register: data
  when:
    - inventory_hostname == groups['group1'][0]

I get the result normally

- name: T14
  debug: msg="data - {{ data | to_nice_json }}"
  when:
    - inventory_hostname == groups['group1'][0]


ok: [host1] => 
  msg: |-
    data - {
        "changed": true,
        "cmd": "/tmp/hosts.json | jq '.[].hostName'",
        "delta": "0:00:00.036695",
        "end": "2023-06-14 22:39:20.125326",
        "failed": false,
        "msg": "",
        "rc": 0,
        "start": "2023-06-14 22:39:20.088631",
        "stderr": "",
        "stderr_lines": [],
        "stdout": "\"host4\"",
        "stdout_lines": [
            "\"host4\""
        ]
    }

I can't figure out how to further process this list in order to execute my command, let's say:

- name: Command
  shell: "ls /tmp"
  when:
    - inventory_hostname == date.standard output....

Do you have any ideas how to do this?

Given the file at host1

shell> ssh admin@host1 cat /tmp/hosts.json
[{"hostName": "host1"}, {"hostName": "host3"}]

Read the file

    - block:
        - command: cat /tmp/hosts.json
          register: out
        - set_fact:
            data: "{{ out.stdout|from_yaml|map(attribute='hostName') }}"
      when: inventory_hostname == groups.group1.0
      run_once: true

This will create the list of data for all hosts when you set run_once: true

    - debug:
        var: data

gives abridged

TASK [debug] **********************************************************************************
ok: [host2] => 
  data:[host1, host3]
ok: [host1] => 
  data:[host1, host3]
ok: [host3] => 
  data:[host1, host3]
ok: [host5] => 
  data:[host1, host3]
ok: [host4] => 
  data:[host1, host3]

Now you can execute the command only on hosts from this file. For example,

    - block:
        - command: date
          register: out
        - debug:
            var: out.stdout
      when: inventory_hostname in data

gives

TASK [command] ********************************************************************************
skipping: [host2]
skipping: [host4]
skipping: [host5]
changed: [host1]
changed: [host3]

TASK [debug] **********************************************************************************
skipping: [host2]
ok: [host1] => 
  out.stdout: Thu Jun 15 04:24:28 UTC 2023
ok: [host3] => 
  out.stdout: Thu Jun 15 04:24:28 UTC 2023
skipping: [host4]
skipping: [host5]

<hr>

<sup>

Example of a complete playbook for testing

- hosts: all

  tasks:

    - block:
        - command: cat /tmp/hosts.json
          register: out
        - set_fact:
            data: "{{ out.stdout|from_yaml|map(attribute='hostName') }}"
      when: inventory_hostname == groups.group1.0
      run_once: true

    - debug:
        var: data|to_yaml

    - block:
        - command: date
          register: out
        - debug:
            var: out.stdout
      when: inventory_hostname in data

<hr>

Use lookup pipe if you want to use jq to parse the data. For example, the set_fact below gives the same list of hosts data

        - set_fact:
            data: "{{ lookup('pipe', cmd).splitlines() }}"
          vars:
            cmd: "echo '{{ out.stdout }}' | jq -r '.[].hostName'"

</sup>