Rust .env

Posted on Jan 11, 2023

Environment Variables

Good practice in software development is parametrizing our environment; for example, if we’re accessing a database and want to store the URL, username, and password, we should parametrize them so we can deploy staging and production environments without changing code.

Enviroment Varaibles in Rust

We can access the environment variables from std::env::var.

use std::env;

fn main() {
    let db_url = env::var("DB_URL").unwrap();
    let db_user = env::var("DB_USER").unwrap();
    let db_pass = env::var("DB_PASS").unwrap();
    println!("{db_url} {db_user} {db_pass}");
}

Then we can run the project.

DB_URL=database.com DB_USER=dbuser DB_PASS=password cargo run

# will output
# database.com dbuser password

Now appending the env variables at the start of the command doesn’t feel right.

.env

The .env will make our parametrizion much easier by storing all our env vars in it.

Add dotenv crate.

cargo add dotenv

Then put your environment variables in a .env file in the form of KEY=value.

DB_URL=database.com
DB_USER=dbuser
DB_PASS=password

# This is a comment
# SECRET_KEY=1234

Finally, call dotnev()

use dotenv::dotenv;
use std::env;

fn main() {
    _ = dotenv();
    let db_url = env::var("DB_URL").unwrap();
    let db_user = env::var("DB_USER").unwrap();
    let db_pass = env::var("DB_PASS").unwrap();
    println!("{db_url} {db_user} {db_pass}");
}

Lots of boilerplates?

Use dotenv_codegen, and getting the environment variable is as simple as dotenv("DB_USER").

cargo add dotenv_codegen

Final code:

#[macro_use]
extern crate dotenv_codegen;
use dotenv::dotenv;

fn main() {
    _ = dotenv();
    let db_url = dotenv!("DB_URL");
    let db_user = dotenv!("DB_USER");
    let db_pass = dotenv!("DB_PASS");
    println!("{db_url} {db_user} {db_pass}");
}