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Showing content from https://docs.deno.com/examples/subprocess_tutorial/ below:

Creating a subprocess

• Concepts
• Simple example
• Security
• Communicating with subprocesses
• Piping to files

• Deno is capable of spawning a subprocess via Deno.Command.
• --allow-run permission is required to spawn a subprocess.
• Spawned subprocesses do not run in a security sandbox.
• Communicate with the subprocess via the stdin, stdout and stderr streams.

This example is the equivalent of running echo "Hello from Deno!" from the command line.

subprocess_simple.ts

const command = new Deno.Command("echo", {
  args: [
    "Hello from Deno!",
  ],
});


const { code, stdout, stderr } = await command.output();

console.assert(code === 0);
console.log(new TextDecoder().decode(stdout));
console.log(new TextDecoder().decode(stderr));

Run it:

$ deno run --allow-run=echo ./subprocess_simple.ts
Hello from Deno!

The --allow-run permission is required for creation of a subprocess. Be aware that subprocesses are not run in a Deno sandbox and therefore have the same permissions as if you were to run the command from the command line yourself.

By default when you use Deno.Command() the subprocess inherits stdin, stdout and stderr of the parent process. If you want to communicate with a started subprocess you must use the "piped" option.

This example is the equivalent of running yes &> ./process_output in bash.

subprocess_piping_to_files.ts

import {
  mergeReadableStreams,
} from "jsr:@std/streams@1.0.0-rc.4/merge-readable-streams";


const file = await Deno.open("./process_output.txt", {
  read: true,
  write: true,
  create: true,
});


const command = new Deno.Command("yes", {
  stdout: "piped",
  stderr: "piped",
});

const process = command.spawn();


const joined = mergeReadableStreams(
  process.stdout,
  process.stderr,
);


joined.pipeTo(file.writable).then(() => console.log("pipe join done"));


setTimeout(() => {
  process.kill();
}, 100);

Run it:

$ deno run --allow-run=yes --allow-read=. --allow-write=. ./subprocess_piping_to_file.ts

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