Ansible: Insert line if not exists

Question

I\'m trying insert a line in a property file using ansible. I want to add some property if it does not exist, but not replace it if such property already exists in the file.

Answer 1

- name: add couchbase.host to properties, works like add or replace
  lineinfile:
    path: /database.properties
    regexp: '^couchbase.host=(?!(127.0.0.1))\b'
    line: 'couchbase.host=127.0.0.1'

This code will replace any line ^couchbase.host=* except couchbase.host=127.0.0.1 or will add new line if it does not exist