Ansible shell module returns error when grep results are empty

Question

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.

Example:

Answer 1

grep by design returns code 1 if the given string was not found. Ansible by design stops execution if the return code is different from 0. Your system is working properly.

To prevent Ansible from stopping playbook execution on this error, you can:

• add ignore_errors: yes parameter to the task

• use failed_when: parameter with a proper condition

Because grep returns error code 2 for exceptions, the second method seems more appropriate, so:

- name: Get the http_status
  shell: grep "http_status=" /var/httpd.txt
  register: cmdln
  failed_when: "cmdln.rc == 2"
  check_mode: no

You might also consider adding changed_when: false so that the task won't be reported as "changed" every single time.

All options are described in the Error Handling In Playbooks document.

Answer 2

Like you observed, ansible will stop execution if the grep exit code is not zero. You can ignore it with ignore_errors.

Another trick is to pipe the grep output to cat. So cat exit code will always be zero since its stdin is grep's stdout. It works if there is a match and also when there is no match. Try it.

- name: Get the http_status
  shell: grep "http_status=" /var/httpd.txt | cat
  register: cmdln
  check_mode: no