title: How to combine variables into new variable?
body: <p>I have Ansible task defined in custom role:</p>
  
  <pre><code>- name: Connect to db
    script: "shell.sh --url={{ db_conn }}"
  </code></pre>
  
  <p>Variable <strong>db_conn</strong> defined in playbook:</p>
  
  <pre><code> vars : 
    db_host: "localhost"
    db_port: 5432
    db_conn: "http://{{ db_host }}:{{ db_port }}"
  </code></pre>
  
  <p>Ansible terminates with error:</p>
  
  <blockquote>
    <p>A variable inserted a new parameter into the module args. Be sure to quote variables if they contain equal signs (for example: "{{var}}").</p>
  </blockquote>