Subprocesses: Spawning

For more complex usecases, we don't simply want the output of some command. In this case, we can spawn a subprocess and interact with it.

The Deno namespace has a unified api for interacting with the outside system called Deno.Command. With it, we can initialize some information about the command but it will not be executed immediately.

const command = new Deno.Command("deno", {
  args: [
    "fmt",
    "-",
  ],
  stdin: "piped",
  stdout: "piped",
});

In a slightly more complex case, we want to interact with a spawned process. To do this, we first need to spawn it.

const process = command.spawn();

We can now pipe the input into stdin. To do this we must first get a writer from the stream and write to it

const writer = process.stdin.getWriter();
writer.write(new TextEncoder().encode("console.log('hello')"));
writer.releaseLock();

We must then close stdin

await process.stdin.close();

We can now wait for the process to output the results

const result = await process.output();
console.log(new TextDecoder().decode(result.stdout));

Run this example locally using the Deno CLI:

deno run --allow-run https://docs.deno.com/by-example/subprocesses-spawn.ts

Additional resources:

Doc: Deno.Command