How to Read Environment Variables from Bnlang

Environment variables are key-value pairs the operating system makes available to a process. They're the standard way to pass configuration (ports, database URLs, secrets) without baking values into the code.

The built-in sys module exposes them; the dotenv library layers a .env file on top for local development.

Reading One Variable

sys.env(name) returns the value as a string, or null if the variable isn't set. Pair it with a default.

import "sys" as sys;

var user = sys.env("USER");
if (user == null) { user = "Guest"; }

print("Current user:", user);

USER=Alice bnl env.bnl
# Output: Current user: Alice

Reading Multiple Variables

import "sys" as sys;

var host = sys.env("HOST"); if (host == null) { host = "localhost"; }
var port = sys.env("PORT"); if (port == null) { port = "3000"; }

print("Server will run at http://" + host + ":" + port);

HOST=127.0.0.1 PORT=8080 bnl config.bnl
# Output: Server will run at http://127.0.0.1:8080

Dumping the Whole Environment

import "sys" as sys;

var all = sys.envs();      // map of every env var
for (var k of all.keys()) {
    print(k, "=", all[k]);
}

Local .env Files with the dotenv Library

For local development you usually don't want to export each variable in the shell. The dotenv library parses a .env file into a map you can read from.

# .env
DATABASE_URL=postgres://localhost/myapp
API_KEY=dev-secret

import "dotenv" as dotenv;

var env = dotenv.load_or_empty(".env");
print(env.DATABASE_URL);
print(env.API_KEY);

Best Practices

Always provide a sensible default for every variable you read.
Keep .env out of version control — commit a .env.example template instead.
Don't log secrets. Treat API_KEY / *_TOKEN / *_SECRET as sensitive.
For multi-environment apps, layer .env.local over .env and let real OS environment variables win at the top.