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denoland-deno/docs/examples/os_signals.md
2020-09-27 13:49:41 -04:00

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# Handle OS Signals
> This program makes use of an unstable Deno feature. Learn more about
> [unstable features](../runtime/stability.md).
## Concepts
- Use the `--unstable` flag to access new or unstable features in Deno.
- [Deno.signal](https://doc.deno.land/builtin/unstable#Deno.signal) can be used
to capture and monitor OS signals.
- Use the `dispose()` function of the Deno.signal
[SignalStream](https://doc.deno.land/builtin/unstable#Deno.SignalStream) to
stop watching the signal.
## Async iterator example
You can use `Deno.signal()` function for handling OS signals:
```ts
/**
* 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:
```shell
deno run --unstable async-iterator-signal.ts
```
## Promise based example
`Deno.signal()` also works as a promise:
```ts
/**
* 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:
```shell
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:
```ts
/**
* 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:
```shell
deno run --unstable dispose-signal.ts
```
The above for-await loop exits after 5 seconds when `sig.dispose()` is called.