Code shared from the Rust Playground

env_var_loop.rs

use std::env;

fn env_vars() {
    // Iterate over all environment variables.
    for (key, value) in env::vars() {
        println!("{}: {}", key, value);
    }

    // You can also filter the environment variables.
    println!("\nFiltered environment variables:");
    for (key, value) in env::vars().filter(|(key, _)| key.starts_with("PATH")) {
        println!("{}: {}", key, value);
    }

    // Get a specific environment variable.
    if let Ok(path) = env::var("PATH") {
        println!("\nPATH: {}", path);
    } else {
        println!("\nPATH environment variable not found.");
    }

    // Get an environment variable, handle missing value gracefully.
    let user = env::var("USER").unwrap_or_else(|_| String::from("unknown"));
    println!("\nUser: {}", user);

    // Using env::vars_os() to get os specific strings.
    println!("\nOS Specific environment variables:");
    for (key_os, value_os) in env::vars_os() {
        if let (Ok(key_str), Ok(value_str)) = (key_os.into_string(), value_os.into_string()) {
            println!("{}: {}", key_str, value_str);
        } else {
            println!("Non-UTF8 env var");
        }
    }

    // Using env::var_os for os specific strings
        if let Some(path_os) = env::var_os("PATH") {
            if let Ok(path_string) = path_os.into_string() {
                println!("\nOS PATH: {}", path_string);
            } else {
                println!("\nOS PATH env var is not valid UTF-8");
            }

        } else {
            println!("\nOS PATH env var not found");
        }
}

fn main() {
  env_vars();
}