How to substitute a variable with a default when it's not empty/undefined?

Question

For the ansible variable param I'd like the behaviour that is similar to the following bash code:

echo ${param:+--arg=}$param

It outputs nothing when the variable is undefined or empty. When the variable has a non-empty value it prints --arg=value.

Is this the best that can be done?

- debug:
  msg: "{{ (param | default('') | length > 0) | ternary('--arg=', '') + (param | default('')) }}"

Vladimir Botka · Accepted Answer · 2023-01-09 18:03:44Z

3

Jinja seems to be simpler

  options: |
    {% if param|d('')|length > 0 %}
    --arg={{ param }}
    {% else %}
    {{ '' }}
    {% endif %}

answered Jan 9, 2023 at 18:03

Vladimir Botka

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3 Comments

TIL you can use jinja2 directly with playbooks

See Flow Scalar Styles. It's very useful to understand the differences among the styles: double-quoted, single-quoted and plain (unquoted).

Thanks for the d() filter. The if/else doesn't make it shorter, but it's clearer.