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user2233709
Asked: 2019-09-27 00:27:27 +0800 CST

Replace a line in a file with Ansible, while ensuring that line is present

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I’m using Ansible and I need to replace a line in a file. The file is a logrotate configuration file for apache /etc/logrotate.d/apache2. Before modification, the line reads

/var/log/apache2/*.log {

which I want to replace with

/var/log/apache2/*.log /var/log/apache2/*/*.log {

I’d rather not rewrite the whole file, not to affect the content of the configuration.

I can do this with the lineinfile module:

- name: Configure logrotate for Apache
  lineinfile:
    dest: /etc/logrotate.d/apache2
    regexp: '^(/var/log/apache2/\*\.log) (?:/var/log/apache2/\*/\*\.log )?{$'
    # The backrefs option is required to ensure the line won’t just be 
    # added, breaking the syntax of the file…
    backrefs: yes
    line: '\1 /var/log/apache2/*/*.log {'

Unfortunately, this task succeeds (with no action) if the regexp is not matched in the configuration file. I’d rather have it fail.

The solution I found is to check the configuration with an extra task:

- name: Check logrotate’s configuration for Apache
  command: egrep '^/var/log/apache2/\*\.log /var/log/apache2/\*/\*\.log {$' /etc/logrotate.d/apache2
  changed_when: no

This seems to work, but I’m unhappy with the duplication of the regexp…

Is there a better way to change a line while failing if that line is not present?

Note that I’m currently stuck with (the quite ancient) Ansible 2.2, but I’m still interested by solutions that work with newer versions.

ansible

1 Answers

  1. Q: "Before modification, the line reads

    /var/log/apache2/*.log {

    which I want to replace with

    /var/log/apache2/*.log /var/log/apache2/*/*.log {

    A: The task below does the job with lineinfile

    - lineinfile:
    path: /etc/logrotate.d/apache2
    regexp: '^(/var/log/apache2/\*\.log)\s+{$'
    line: '\1 /var/log/apache2/*/*.log {'
    backrefs: yes

    Q: "Is there a better way to change a line while failing if that line is not present?"

    A: The task below fails when pattern is not in the configuration file

       - fail:
        msg: Pattern not in file
      when: not lookup('file', my_conf).splitlines()|
            select('match', pattern)|list
      vars:
        pattern: '^/var/log/apache2/\*\.log\s+{$'
        my_conf: '/etc/logrotate.d/apache2'

   - replace:
       path: /etc/logrotate.d/apache2
       regexp: '^(/var/log/apache2/\*\.log)\s+{$'
       replace: '\1 /var/log/apache2/*/*.log {'
    • 3