CodeIgniter makes it simple and effortless to set Environment Variables by using a “dotenv” (.env) file. CodeIgniter expects .env to be at the root of your project beside the system and app directories.
There is an env file at the project root in CodeIgniter. You can use this file as a starting place for your application by renaming the template to .env or by making a copy of it named .env.
In .env file a collection of name/value pairs separated by an equal sign.
CI_ENVIRONMENT = development