Using an environment variable (from `.env` file) in custom Twig function in Symfony 4

Here’s an easier way (Symfony 4) that does not involve any custom extensions. In my case, I wanted to set the Google Tag Manager Id as an environment variable in the .env file:

GOOGLE_TAG_MANAGER_ID="GTM-AAA12XX"

Next, reference the environment variable in the config/packages/twig.yaml file:

twig:
    globals:
        google_tag_manager_id: '%env(GOOGLE_TAG_MANAGER_ID)%'

Now you can use the tag manager value in your Twig templates like this:

{{ google_tag_manager_id }}

For a production system, you may not have a .env file. In that case, set the variable in your Apache config file:

SetEnv GOOGLE_TAG_MANAGER_ID GTM-AAA12XX

I have not tested things with nginx config files, but I think this should work:

fastcgi_param GOOGLE_TAG_MANAGER_ID "GTM-AAA12XX";

For more details, see the Symfony documentation for Configuration Based on Environment Variables, and Environment Variable Processors. Environment Variable Processors let you do things like trim variables or set defaults.