passing var to role arg

foo

# /tmp/foo
bar

gistfile1.txt

PLAY [all] ********************************************************************

TASK: [register a fact] *******************************************************
changed: [localhost]

PLAY [all] ********************************************************************

TASK: [tmp | do something] ****************************************************
ok: [localhost] => {
    "item": "",
    "myvar": "bar"
}

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

main.yml

# /etc/ansible/roles/tmp/tasks/main.yml
---
- name: do something
  debug: var=myvar

tmp.yml

# /etc/ansible/tmp.yml
---
- hosts: all
  gather_facts: no
  tasks:
    - name: register a fact
      command: cat /tmp/foo
      register: output

- hosts: all
  gather_facts: no
  roles:
    - { role: tmp, myvar: "{{ output.stdout }}" }