title: Ansible shell module returns error when grep results are empty
body: <p>I am using Ansible's shell module to find a particular string and store it in a variable. But if grep did not find anything I am getting an error.</p>
  
  <p>Example:</p>
  
  <pre><code>- name: Get the http_status
    shell: grep "http_status=" /var/httpd.txt
    register: cmdln
    check_mode: no
  </code></pre>
  
  <p>When I run this Ansible playbook if <code>http_status</code> string is not there, playbook is stopped. I am not getting stderr.</p>
  
  <p>How can I make Ansible run without interruption even if the string is not found?</p>