---
- name: Defining variable through command line and using it in playbook below
  hosts: nodes
  tasks:
    - name: Installing packages
      yum:
        name: "{{ rpm }}"
        state: latest
...
# We have to define a variable value while executing the playbook.
# ansible-playbook cmdline_variable -e rpm=zsh these value will pass here inside playbook { -e is to add variable value }