Using environment variables in the site configuration 

Environment variables in the site configuration allows setting placeholders for configuration options that get replaced by environment variables specific to the current environment.

The format for environment variables is %env(ENV_NAME)%. Environment variables may be used to replace complete values or parts of a value.

Examples 

base: 'https://%env(BASE_DOMAIN)%/'
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When using environment variables in conditions, make sure to quote them correctly:

condition: '"%env(my_env)%" == "my_comparison_string"'
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