os_signals.md

Handle OS Signals

This program makes use of an unstable Deno feature. Learn more about unstable features.

Concepts

• Use the --unstable flag to access new or unstable features in Deno.
• Deno.signal can be used to capture and monitor OS signals.
• Use the dispose() function of the Deno.signal SignalStream to stop watching the signal.

Async iterator example

You can use Deno.signal() function for handling OS signals:

/**
 * async-iterator-signal.ts
 */
console.log("Press Ctrl-C to trigger a SIGINT signal");
for await (const _ of Deno.signal(Deno.Signal.SIGINT)) {
  console.log("interrupted!");
  Deno.exit();
}

Run with:

deno run --unstable async-iterator-signal.ts

Promise based example

Deno.signal() also works as a promise:

/**
 * promise-signal.ts
 */
console.log("Press Ctrl-C to trigger a SIGINT signal");
await Deno.signal(Deno.Signal.SIGINT);
console.log("interrupted!");
Deno.exit();

Run with:

deno run --unstable promise-signal.ts

Stop watching signals

If you want to stop watching the signal, you can use dispose() method of the signal object:

/**
 * dispose-signal.ts
 */
const sig = Deno.signal(Deno.Signal.SIGINT);
setTimeout(() => {
  sig.dispose();
  console.log("No longer watching SIGINT signal");
}, 5000);

console.log("Watching SIGINT signals");
for await (const _ of sig) {
  console.log("interrupted");
}

Run with:

deno run --unstable dispose-signal.ts

The above for-await loop exits after 5 seconds when sig.dispose() is called.