List extra-vars provided to the playbook - ansible

Question

I have following scaled down version of playbook and I need to find out the list of extra-vars passed to this playbook. This is needed because sometimes user by typing mistake provide incorrect name of the extravar and the playbook will not use misspelled variable. SO I need to make sure user provide correct name of the extravar`.
---
- hosts: localhost
vars:
restart: 'on'
tasks:
- name: "WHEN CONDITION CHECK"
shell: echo reboot
when: "'off' in restart "
Example:
#This should run
ansible-playbook playbook.yml -e restart=off
#This should get detected, like some extra var is passed.
ansible-playbook playbook.yml -e restarttt=off
Note: I already know restart is not defined check, I am trying to find the list of vars. As I want to use defaults also, So cannot use not defined check.
I am expecting to print following as output:
restart
restarttt

Answer 1

If you run below code
- hosts: all
gather_facts: True
tasks:
- name: host
debug: var=vars
You will find your extra vars in the JSON structure, but it seems that it goes to the 'root' of the tree and to hostvars 'branch'
Hope it helps.

Answer 2

You may leverage /proc/<process-pid>/cmdline file to read the command line arguments passed to the ansible playbook.
---
- hosts: localhost
gather_facts: False
tasks:
- name: "Get the command line args"
shell: "cat -A /proc/{{ lookup('pipe', 'echo $PPID') }}/cmdline |sed -r 's/\\^#/ /g'"
register: cmd_line
delegate_to: localhost
- name: "Print the arguments passed to the playbook"
debug:
msg: "{{ cmd_line.stdout.split(' ')|select() }}"
Example:
ansible-playbook foo.yml -i inventory.yml -e foo=123 -e 'bar=0 zoo=1'
PLAY [localhost] ********************************************************************************************************************************************************************************************************************
TASK [Get the command line args] ****************************************************************************************************************************************************************************************************
changed: [127.0.0.1 -> localhost]
TASK [Print the arguments passed to the playbook] ***********************************************************************************************************************************************************************************
ok: [127.0.0.1] => {
"msg": [
"/usr/bin/python3",
"/home/p/.local/bin/ansible-playbook",
"foo.yml",
"-i",
"inventory.yml",
"-e",
"foo=123",
"-e",
"bar=0",
"zoo=1"
]
}
Once you have the list of args passed to the ansible-playbook you may write whatever logic is needed.
Note: the file /proc/<pid>/cmdline is having null separated list of arguments; you might want to write a better parsing logic if your code break at any point.