The .env file is a text file that contains environment variables, commonly used store configuration settings for an application. It is written in a key-value pair format similar to a shell script.

• Some runtimes loads .env files automatically.

  • Vite loads .env files automatically, making them available as import.meta.env. As a result, frameworks based on Vite also inherit this behavior, such as Astro and SvelteKit. Do note that for these frameworks, environment variables may be evaluated at build time or runtime¹ and behavior can be different between development and production environments, so refer to the documentation for specifics.

  • Glitch, a platform for building web applications, automatically loads .env files in a project as a normal environment variable.

  • Docker Compose automatically loads .env files for the purpose of interpolation into the docker-compose.yml file. Note that this does not make the environment variables available to the containers managed by Docker Compose.

    More details for Docker Compose

    To make the environment variables available to the containers, specify the environment variable names in the environment section of the docker-compose.yml file. For example:

    services:
      myservice:
        image: myimage
        environment:
          - MY_ENV_VAR

    Docker Compose will pass on the contents of the MY_ENV_VAR environment variable (which may be automatically loaded from the .env file) to the container.

    Alternatively, if you want all environment variables from the .env file to be passed to the container, you can use the env_file directive in the docker-compose.yml file.

  • Bun loads .env files automatically.

• Some runtimes lets you load a .env file, but it must be explicitly done.

  • Node.js has support for --env-file since v20.

• Program your application to load the .env file.

  • Ruby apps can use the dotenv gem to load the .env file at startup.

  • Node.js apps can use the dotenv package to load the .env file at startup.

• Run your application through a wrapper that loads the .env file.

  • dotenvx lets you run arbitrary commands with environment variables loaded from a .env file.

    More details for dotenvx

    To run a command with .env file loaded:

    dotenvx run -- command

    To specify the .env file to load:

    dotenvx run -f .env.ci -- command

  • Docker lets you specify the --env-file for the container.

• Load variables from .env file into the shell.

  • direnv is a shell extension that loads (and unloads) environment variables from a .env file into the shell when you cd into (and out of) a directory. More advanced configuration can be done by using a .envrc file instead. (Nowadays I use mise-en-place instead of direnv.)

  • mise-en-place can automatically load the .env file in a directory by configuring it in .mise.toml.