.env Loader

The gist: build a library that loads a .env file from disk and sets environment variables from the specified files.

When working on software, especially web servers, there's a need to configure global settings. Whether it's an API URL or a secure token, you won't want those values committed in the source. So people configure their applications via environment variables.

When working on your own computer, it's a pain to manage environment variables for all of the various applications you may be working on. So a common pattern is to specify a .env file that's ignored by Git and have that be loaded into the environment variables for your application.

The goal of this project is to write a library that loads and parses a .env and loads those values into the environment that your application can then access. If the file is missing, don't load it.


Here's what a simple .env file would be like. The syntax is that each line is KEY=value where the key is SCREAMING_SNAKE_CASE, and = sign to separate, and the value is any chars following that.


When the library runs, it should parse that file and insert those keys and values into the environment.


  • Write a function or entry-point into the lib for loading the .env file in the project root
  • Ensure the environment keys and values are properly set and accessible within the code using the lib
  • Support custom path to the .env file
  • Don't load the .env if it's not present
  • Error if any line is improperly formatted
    • But be okay with empty lines


  • Parsing files
  • Validating file is correct
  • Working with the environment

Extra Credit

  • Support per-environment configs (.env.test, .env.dev, etc.)
  • Explore setting the environment variables just for the program that uses the library or globally for the entire running OS. What are the pros and cons of this?
  • Allow for comments with lines that start with # or //
  • Are there other formats you'd prefer over this simple approach like JSON or TOML or YAML? Support it!
  • While sensitive data is often configured via environment variables, sometimes you have config data that isn't sensitive. What if you extended this library or made a separate library that loads config settings via a JSON, YAML, or TOML and made them easily accessible within the codebase? That'd be useful!