在 Ansible 剧本中将变量插入花括号的最易读方式

Question

I'm trying to use the loop feature to set the following lines in a config file:

$nrconf{kernelhints} = 0;
$nrconf{ucodehints} = 0;

The code below fails with "jinja2.exceptions.TemplateSyntaxError: unexpected '}'".

- name: disable kernelhints on apt install
  lineinfile:
    path: /etc/needrestart/needrestart.conf
    regexp: '^.*\$nrconf\{{{ item }}\}.*$'
    line: '$nrconf\{{{ item }}\} = 0;'
  loop:
    - 'kernelhints'
    - 'ucodehints'

I understand that I can use either {% raw %} or {{ '{' }}{{ item }} or {{ '{' + item }} approach, but the resulting code look makes me sad. Is there any trick to make the code clean and clear?

Answer 1

You could use string formatting:

    - name: disable kernelhints on apt install
      lineinfile:
        path: needrestart.conf
        regexp: '{{ "^.*\$nrconf{%s}.*$" % item }}'
        line: '{{ "$nrconf{%s} = 0" % item }}'
      loop:
        - 'kernelhints'
        - 'ucodehints'

I think that's a little more clear.

When writing this sort of thing for myself, I try to avoid nested quotes and instead use some of YAML's quote operators, like this:

    - name: disable kernelhints on apt install
      lineinfile:
        path: needrestart.conf
        regexp: >-
          {{ "^.*\$nrconf{%s}.*$" % item }}
        line: >-
          {{ "$nrconf{%s} = 0" % item }}
      loop:
        - 'kernelhints'
        - 'ucodehints'

Operationally it's identical, but it removes one level of quoting so that you don't go insane if you need nested quotes inside your expression.

Answer 2

In regexp , put the braces into brackets. In line , concatenate the strings

        regexp: '^.*\$nrconf[{]{{ item }}[}].*$'
        line: "{{ '$nrconf{' ~ item ~ '} = 0;' }}"

---

Example of a complete playbook for testing

shell> cat pb.yml - hosts: localhost tasks: - name: disable kernelhints on apt install lineinfile: path: /tmp/needrestart.conf regexp: '^.*\$nrconf[{]{{ item }}[}].*$' line: "{{ '$nrconf{' ~ item ~ '} = 0;' }}" loop: - kernelhints - ucodehints

For example, given the file

shell> cat /tmp/needrestart.conf $nrconf{undef} = 0;

The playbook gives running with --check --diff options

shell> ansible-playbook pb.yml -CD PLAY [localhost] ***************************************************************************** TASK [disable kernelhints on apt install] **************************************************** --- before: /tmp/needrestart.conf (content) +++ after: /tmp/needrestart.conf (content) @@ -1 +1,2 @@ $nrconf{undef} = 0; +$nrconf{kernelhints} = 0; changed: [localhost] => (item=kernelhints) --- before: /tmp/needrestart.conf (content) +++ after: /tmp/needrestart.conf (content) @@ -1 +1,2 @@ $nrconf{undef} = 0; +$nrconf{ucodehints} = 0; changed: [localhost] => (item=ucodehints) PLAY RECAP *********************************************************************************** localhost: ok=1 changed=1 unreachable=0 failed=0 skipped=0 rescued=0 ignored=0

The result

shell> cat /tmp/needrestart.conf $nrconf{undef} = 0; $nrconf{kernelhints} = 0; $nrconf{ucodehints} = 0;