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

User robo's regexp & absent method is quite clean, so I've fleshed it out here for easy use and added improvements from comments by @assylias and @Olivier:

- name: Ensure /tmp/my.conf contains 127.0.0.1
  lineinfile:
    path: /tmp/my.conf
    regexp: '^127\.0\.0\.1.*whatever'
    state: absent
  check_mode: yes
  changed_when: false
  register: out

- debug:
    msg: "Yes, line exists."
  when: out.found

- debug:
    msg: "Line does NOT exist."
  when: not out.found

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)


- name: Check whether /tmp/my.conf contains "127.0.0.1"
  command: grep -Fxq "127.0.0.1" /tmp/my.conf
  register: checkmyconf
  check_mode: no
  ignore_errors: yes
  changed_when: no

- name: Greet the world if /tmp/my.conf contains "127.0.0.1"
  debug: msg="Hello, world!"
  when: checkmyconf.rc == 0

Update 2017-08-28: Older Ansible versions need to use always_run: yes instead of check_mode: no.


With the accepted solution, even though you ignore errors, you will still get ugly red error output on the first task if there is no match:

TASK: [Check whether /tmp/my.conf contains "127.0.0.1"] ***********************
failed: [localhost] => {"changed": false, "cmd": "grep -Fxq "127.0.0.1" /tmp/my.conf", "delta": "0:00:00.018709", "end": "2015-09-27 17:46:18.252024", "rc": 1, "start": "2015-09-27 17:46:18.233315", "stdout_lines": [], "warnings": []}
...ignoring

If you want less verbose output, you can use awk instead of grep. awk won't return an error on a non-match, which means the first check task below won't error regardless of a match or non-match:

- name: Check whether /tmp/my.conf contains "127.0.0.1"
  command: awk /^127.0.0.1$/ /tmp/my.conf
  register: checkmyconf
  changed_when: False

- name: Greet the world if /tmp/my.conf contains "127.0.0.1"
  debug: msg="Hello, world!"
  when: checkmyconf.stdout | match("127.0.0.1")

Notice that my second task uses the match filter as awk returns the matched string if it finds a match.

The alternative above will produce the following output regardless of whether the check task has a match or not:

TASK: [Check whether /tmp/my.conf contains "127.0.0.1"] ***********************
ok: [localhost]

IMHO this is a better approach as you won't ignore other errors in your first task (e.g. if the specified file did not exist).

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