Environment Variables

Reading an environment variable is one of the simplest I/O operations there is, but access differs slightly: Node.js treats process.env like an object; Go, Rust, and Java all use a function that takes the variable's name, while Swift indexes the environment dictionary with a subscript. Go returns an empty string when the variable doesn't exist, Rust returns a Result (use unwrap_or_default() to get a similarly empty string), and Swift and Java return nil/null.

Reading an environment variable

const key = process.env['API_KEY']
 
console.log(key)

package main
 
import (
	"fmt"
	"os"
)
 
func main() {
	key := os.Getenv("API_KEY")
 
	fmt.Println(key)
}

use std::env;
 
fn main() {
    let key = env::var("API_KEY").unwrap_or_default(); // Err if the variable is missing or not valid UTF-8
    println!("{key}");
}

import Foundation
 
let key = ProcessInfo.processInfo.environment["API_KEY"] ?? ""
print(key)

void main() {
    String key = System.getenv("API_KEY"); // null if the variable doesn't exist
    IO.println(key);
}

$ API_KEY=foobar node env_vars.js
foobar
 
$ API_KEY=foobar go run env_vars.go
foobar
 
$ API_KEY=foobar cargo run
foobar
 
$ API_KEY=foobar swift env_vars.swift
foobar
 
$ API_KEY=foobar java Main.java
foobar