Variable is undefined when running Ansible 'debug' ad-hoc - ansible

Question

Could you explain why following behaviour happens. When I try to print remote Ansible IP with following playbook everything works as expected:
---
- hosts: centos1
tasks:
- name: Print ip address
debug:
msg: "ip: {{ansible_all_ipv4_addresses[0]}}"
when I try ad-hoc command it doesn't work:
ansible -i hosts centos1 -m debug -a 'msg={{ansible_all_ipv4_addresses[0]}}'
Here is the ad-hoc error:
centos1 | FAILED! => {
"msg": "The task includes an option with an undefined variable. The error was: 'ansible_all_ipv4_addresses' is undefined.
'ansible_all_ipv4_addresses' is undefined" }
I don't find any difference in both approaches that is why I was expecting both to work and print the remote IP address.

Answer 1

I don't find any difference in both approaches that is why I was expecting both to work and print the remote IP address.
This is because no facts were gathered. Whereby via ansible-playbook and depending on the configuration Ansible facts become gathered automatically, via ansible only and ad-hoc command not.
To do so you would need to execute the setup module instead. See Introduction to ad hoc commands - Gathering facts.
Further Q&A
How Ansible sets variables?
Why does Ansible ad-hoc debug module not print variable?
Please take note of the variable names according
Conflict of variable name packages with ansible_facts.packages
Could you please give some example on How to output "Your IP address is "{{ ansible_all_ipv4_addresses[0] }}"? using ad-hoc approach with setup module?
Example
ansible test.example.com -m setup -a 'filter=ansible_all_ipv4_addresses'
test.example.com | SUCCESS => {
"ansible_facts": {
"ansible_all_ipv4_addresses": [
"192.0.2.1"
]
},
"changed": false
}
or
ansible test.example.com -m setup -a 'filter=ansible_default_ipv4'
test.example.com | SUCCESS => {
"ansible_facts": {
"ansible_default_ipv4": {
"address": "192.0.2.1",
"alias": "eth0",
"broadcast": "192.0.2.255",
"gateway": "192.0.2.0",
"interface": "eth0",
"macaddress": "00:00:5e:12:34:56",
"mtu": 1500,
"netmask": "255.255.255.0",
"network": "192.0.2.0",
"type": "ether"
}
},
"changed": false
}
It is also recommend to have a look into the full output without the filter argument to get familiar with the result set and data structure.
Documentation
setup module - Examples