Environment Variables

Environment variables can be used to configure the behavior of a program, or pass data from one program to another.

Here an environment variable with the name "PORT" is read. If this variable is set the return value will be a string. If it is unset it will be `undefined`.

const PORT = Deno.env.get("PORT");
console.log("PORT:", PORT);

You can also get an object containing all environment variables.

const env = Deno.env.toObject();
console.log("env:", env);

Environment variables can also be set. The set environment variable only affects the current process, and any new processes that are spawned from it. It does not affect parent processes or the user shell.

Deno.env.set("MY_PASSWORD", "123456");

You can also unset an environment variable.

Deno.env.delete("MY_PASSWORD");

Note that environment variables are case-sensitive on unix, but not on Windows. This means that these two invocations will have different results between platforms.

Deno.env.set("MY_PASSWORD", "123");
Deno.env.set("my_password", "456");
console.log("UPPERCASE:", Deno.env.get("MY_PASSWORD"));
console.log("lowercase:", Deno.env.get("my_password"));

Access to environment variables is only possible if the Deno process is running with env var permissions (`--allow-env`). You can limit the permission to only a specific number of environment variables (`--allow-env=PORT,MY_PASSWORD`).

Run this example locally using the Deno CLI:

deno run --allow-env https://examples.deno.land/environment-variables.ts

Additional resources:

Handling OS Signals Subprocesses: Collecting Output