Only check whether a line present in a file (ansible)

Question

In ansible, I need to check whether a particular line present in a file or not. Basically, I need to convert the following command to an ansible task. My goal is to only check.

grep -Fxq "127.0.0.1" /tmp/my.conf

Answer 1

Use check_mode, register and failed_when in concert. This fails the task if the lineinfile module would make any changes to the file being checked. Check_mode ensures nothing will change even if it otherwise would.

- name: "Ensure /tmp/my.conf contains '127.0.0.1'"
  lineinfile:
    name: /tmp/my.conf
    line: "127.0.0.1"
    state: present
  check_mode: yes
  register: conf
  failed_when: (conf is changed) or (conf is failed)