rust config environment

Environment variables with std::env for configuration

Marcus Chen Jan 2026

1 tab

use std::env;

fn main() {
    let port: u16 = env::var("PORT")
        .unwrap_or_else(|_| "8080".to_string())
        .parse()
        .expect("PORT must be a number");

    println!("Server will run on port {}", port);
}

1 file · rust Explain with highlit

Reading environment variables is a common way to configure applications. std::env::var("KEY") returns Result<String, VarError>, which you handle with ? or .unwrap_or_else(). I use env vars for secrets, runtime config, and feature flags. For parsing into types, use .parse() with ?. For optional vars, match on Ok/Err. I centralize env reading in a config struct at startup to catch missing vars early. For complex config, combine env vars with files (using dotenv or envy crates). Environment variables are simple, portable, and well-supported in deployment environments like Docker and Kubernetes.