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

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

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.

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

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).

Use ansible lineinfile command, but this command will update the file with the line if it does not exists.

- lineinfile: dest=/tmp/my.conf line='127.0.0.1' state=present

Another way is to use the "replace module" then "lineinfile module".

The algo is closed to the one used when you want to change the values of two variables.

• First, use "replace module" to detect if the line you are looking for is here and change it with the something else. (Like same line + something at the end).
• Then if "replace" is true, It means your line is here then replace the new line with a particularity, with the new line looking.
• Else the line you are looking for is not here.

Example:

# Vars
- name: Set parameters
  set_fact:
    newline      : "hello, i love ansible"
    lineSearched : "hello"
    lineModified : "hello you"

# Tasks
- name: Try to replace the line
  replace:
    dest    : /dir/file
    replace : '{{ lineModified }} '
    regexp  : '{{ lineSearched }}$'
    backup  : yes
  register  : checkIfLineIsHere

- name: Line is here, change it
  lineinfile:
    state   : present
    dest    : /dir/file
    line    : '{{ newline }}'
    regexp  : '{{ lineModified }}$'
  when: checkIfLineIsHere.changed

• If the file contains "hello", it will become "hello you" then "hello, i love ansible" at the end.
• If the file content doesn't contain "hello", the file is not modified.

With the same idea, you can do something if the lineSearched is here:

# Vars
- name: Set parameters
  set_fact:
    newline      : "hello, i love ansible"
    lineSearched : "hello"
    lineModified : "hello you"

# Tasks
- name: Try to replace the line
  replace:
    dest    : /dir/file
    replace : '{{ lineModified }} '
    regexp  : '{{ lineSearched }}$'
    backup  : yes
  register  : checkIfLineIsHere

# If the line is here, I want to add something.
- name: If line is here, do something
  lineinfile:
    state   : present
    dest    : /dir/file
    line    : '{{ newline }}'
    regexp  : ''
    insertafter: EOF
  when: checkIfLineIsHere.changed

# But I still want this line in the file, Then restore it
- name: Restore the searched line.
  lineinfile:
    state   : present
    dest    : /dir/file
    line    : '{{ lineSearched }}'
    regexp  : '{{ lineModified }}$'
  when: checkIfLineIsHere.changed

• If the file contains "hello", the line will still contain "hello" and "hello, i love ansible" at the end.
• If the file content doesn't contain "hello", the file is not modified.

You can use the file plugin for this scenario.

To set a fact you can use in other tasks ... this works.

- name: Check whether /tmp/my.conf contains "127.0.0.1"
  set_fact:
    myconf: "{{ lookup('file', '/tmp/my.conf') }}"  
  ignore_errors: yes

- name: Greet the world if /tmp/my.conf contains "127.0.0.1"
  debug: msg="Hello, world!"
  when: "'127.0.0.1' in myconf"

To check the file content as a condition of a task ... this should work.

- name: Greet the world if /tmp/my.conf contains "127.0.0.1"
  debug: msg="Hello, world!"
  when: "'127.0.0.1' in lookup('file', '/tmp/my.conf')"

Another solution, also useful for other purposes is to loop over the contents of the file, line by line

- name: get the file
  slurp:
    src: /etc/locale.gen
  register: slurped_file

- name: initialize the matches list
  set_fact:
    MATCHES: []

- name: collect matches in a list
  set_fact:
    MATCHES: "{{ MATCHES + [line2match] }}"
  loop: "{{ file_lines }}"
  loop_control:
    loop_var: line2match
  vars:
    - decode_content: "{{ slurped_file.content | b64decode }}"
    - file_lines: "{{ decode_content.split('\n') }}"
  when: '"BE" in line2match'
  
- name: report matches if any
  debug:
    msg: "Found {{ MATCHES | length }} matches\n{{ MATCHES }}"
  when: 'listlen | int > 0'
  vars:
    listlen: "{{ MATCHES | length }}"

This mechanism can be use to get a specific value from a matched line if you use it for example with the jinja regex_replace filter