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std/env ​

Environment variable access.

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from "std/env" import { Env }

Functions ​

Env.get ​

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fn Env.get(name: string): Option<string>

Look up an environment variable. Returns None if unset.

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match Env.get("HOME") {
    Some(home) => writeStdout(home),
    None => writeStdout("HOME not set"),
}

Env.getOr ​

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fn Env.getOr(name: string, fallback: string): string

Look up an environment variable with a default.

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let port = Env.getOr("PORT", "8080")

Env.set ​

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fn Env.set(name: &string, value: &string): Result<Unit, EnvError>

Set a variable in this process's environment, replacing any current value. Children spawned afterwards inherit it; the parent shell never sees it. To give one child a variable without changing your own environment, use Command.env in std/process.

EnvError.InvalidName means the name was empty or contained =.

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let _ = Env.set("RUST_LOG", "debug")!

Not thread-safe

C's setenv may free the block a concurrent getenv is reading, and no platform offers a thread-safe version. It is safe from a single-threaded program and from green tasks (which never switch inside this call), but not concurrently with Promise.blocking work, which runs on real OS threads and may call getenv through any C library. Set the environment during startup, before spawning anything — the same advice Go and Rust give.

Env.remove ​

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fn Env.remove(name: &string): Result<Unit, EnvError>

Remove a variable from this process's environment. Removing a name that is not set succeeds. Same thread-safety limits as Env.set.