get the value from a dict using filter

Question

I have a dictionary, not a dict list, let's say I read a dict from JSON file something.json has content {"a": "b"}

I would like to extract the value using a filter, so I could process that with more filters

# Expecting 'lookup('file', 'something.json') | from_json | ???' gives the value 'b'
- debug:
    msg: "{{ lookup('file', 'something.json') | from_json | ??? | urlencode() }}"

I searched that all other examples are for dict list, but I only have a dict here

Answer 1

Given the file below

shell> cat something.json 
{"a": "b"}

---

Q: "Get the value from a dict using a filter."

A: I read your question: "Get the value from a hash without knowing the key." There are many options:

1. Include the variable from the file to a dictionary, e.g. d1, and display the first value

- hosts: localhost
  tasks:
    - include_vars:
        file: something.json
        name: d1
    - debug:
        msg: "{{ d1.values() | first }}"

gives

shell> ansible-playbook pb.yml

PLAY [localhost] *****************************************************************************

TASK [include_vars] **************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************
ok: [localhost] => 
  msg: b

PLAY RECAP ***********************************************************************************
localhost: ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---

2. You can put the declarations into the vars

- hosts: localhost
  vars:
    d1: "{{ lookup('file', 'something.json') }}"
    v1: "{{ d1.values() | first }}"
  tasks:
    - debug:
        var: v1
    - debug:
        var: d1 | type_debug
    - debug:
        var: d1

gives

PLAY [localhost] *****************************************************************************

TASK [debug] *********************************************************************************
ok: [localhost] => 
  v1: b

TASK [debug] *********************************************************************************
ok: [localhost] => 
  d1|type_debug: dict

TASK [debug] *********************************************************************************
ok: [localhost] => 
  d1:
    a: b

PLAY RECAP ***********************************************************************************
localhost: ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---

3. Use json_query

- hosts: localhost
  vars:
    d1: "{{ lookup('file', 'something.json') }}"
    v1: "{{ d1 | json_query('values(@)') | first }}"
  tasks:
    - debug:
        var: v1

gives

PLAY [localhost] *****************************************************************************

TASK [debug] *********************************************************************************
ok: [localhost] => 
  v1: b

PLAY RECAP ***********************************************************************************
localhost: ok=1    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---

All the above options assume the file is available at the controller. If the file is at the remote host:

4. Use slurp

- hosts: localhost
  vars:
    d1: "{{ out.content|b64decode }}"
    v1: "{{ d1.values() | first }}"
  tasks:
    - slurp:
        src: "{{ playbook_dir }}/something.json"
      register: out
    - debug:
        var: v1

gives

PLAY [localhost] *****************************************************************************

TASK [slurp] *********************************************************************************
ok: [localhost]

TASK [debug] *********************************************************************************
ok: [localhost] => 
  v1: b

PLAY RECAP ***********************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---

5. You can also register the output of cat

- hosts: localhost
  vars:
    d1: "{{ out.stdout }}"
    v1: "{{ d1.values() | first }}"
  tasks:
    - command:
        cmd: "cat something.json"
        chdir: "{{ playbook_dir }}"
      register: out
    - debug:
        var: v1

gives

PLAY [localhost] *****************************************************************************

TASK [command] *******************************************************************************
changed: [localhost]

TASK [debug] *********************************************************************************
ok: [localhost] => 
  v1: b

PLAY RECAP ***********************************************************************************
localhost: ok=2    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0

---