Subprocesses: Collecting output

We don't often write programs in isolation. In a lot of cases we want to interact with the outside system and spawning a subprocess is a common way to do this.

Edit on Github

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: [
    "eval",
    "\
    console.log('hello from deno'); \
    console.error('hello from stderr'); \
    ",
  ],
});

In the most simple case we just want to run the process to completion. This can be achieved using command.output()

let result = await command.output();

It can also be achieved synchronously using command.outputSync()

result = command.outputSync();

We can now interact with stdout and stderr

const textDecoder = new TextDecoder();
console.log("stdout:", textDecoder.decode(result.stdout));
console.log("stderr:", textDecoder.decode(result.stderr));

Run this example locally using the Deno CLI:

deno run --allow-run https://docs.deno.com/examples/subprocesses-output.ts

Additional resources

Doc: Deno.Command