Load Environment Variables From ".env" Files In Your Rust Program

A good practice in software development is to separate the “secrets” — such as API Tokens — from your source code. Otherwise, people, when visualizing the code could take those secrets, and that represents a security breach.

Today, I was working on setting up a newsletter on my website, that’s open source, and had the need MAILCOACH_API_TOKEN to interact with the mailcoach.app. Now, because my website is built on Rust, I’ve used the dotenv crate to collect environment variables from a “.env” file.

So, first I’ve used cargo to add the dotenv to my project:

cargo add dotenv

After, I’ve created a .env file in the root of my project, and inserted the necessary API TOKEN there:

MAILCOACH_API_TOKEN=my_api_token_here

Next, I’ve changed the entry point of my Rust program src/bin/server.rs to load these environment variables when my program starts:

use dotenv::dotenv;

fn main() {
    dotenv().ok(); // This line loads the environment variables from the ".env" file.

    // ..
}

Finally, I’ve adjusted the code to collect the Mailcoach API Token when necessary using the standard library:

let mailcoach_api_token = std::env::var("MAILCOACH_API_TOKEN").expect("MAILCOACH_API_TOKEN must be set.");

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