Is there a way to build up a single string from a list of values using standard Ansible/Jinja2 templating syntax?

Question

I have a variable that looks something like this:

files:
  - a.yaml
  - b.yaml
  - c.yaml

Using the ansible.builtin.template module, I'd like to build a file which contains the following string:

OPTIONS="--config=a.yaml --config=b.yaml --config.yaml"

I can't hard-code this as I don't always know:

1. How many files there will actually be
2. What the names of the files will be

...because they may be set via any one of Ansible's variable setting options (host|group_vars, role defaults etc.). This means I need to "build" it up and then "inject" it into a template somehow.

Is there a way to build up a string from a list like this?

Thanks!

Answer 1

You can achieve this by using the join filter in Ansible.

Here i provide an example playbook that demonstrates how you can build your desired string from the list of files (not limited to 3 files) using the join filter:

---
- name: Build string from a list in Ansible
  hosts: <your_target_hosts>
  gather_facts: false  # here you can adjust this based on your needs

  tasks:
    - name: Set the list of files
      set_fact:
        files_list:
          - a.yaml
          - b.yaml
          - c.yaml

    - name: Build the OPTIONS string
      set_fact:
        options_string: "--config={{ files_list | join(' --config=') }}"

    - name: Debug the OPTIONS string ( to show the value )
      debug:
        var: options_string

Now, you can use the "options_string" variable in your template module or other tasks as you need