Accessing OS environment variables from Jinja2 template

Question

Is it possible to access a OS environment variable directly from a Jinja2 template?

Answer 1

Following @Renier's pointer about custom filters in the comments, I figured out a possible solution.

Define a custom filter:

def env_override(value, key):
  return os.getenv(key, value)

Install the filter in the environment:

env.filters['env_override'] = env_override

Use the filter as follows:

"test" : {{ "default" | env_override('CUSTOM') }}

Where the appropriate environment variable can be set as:

export CUSTOM=some_value

If the environment variable is set the output will be:

"test" : some_value

Otherwise:

"test" : default