Spawning a Process

You might want to spawn a process to interact with external tools or programs.

To do this, you can use the spawn function from the child_process module.

INFO

This module is similar to NodeJS's child_process module, but with some differences. You can find more information in the child_process documentation.

Launching a process

The code below spawns a process that echoes "Hello, world!" to the console.

import { spawn } from "child_process";

const child = spawn("echo", ["Hello, world!"]);

Reading STDOUT and STDERR

To handle the output and error streams of the child process, you can use the stdout and stderr properties of the child process.

let output = "";
child.stdout.on("data", (data) => {
  output += data.toString();
});

let error = "";
child.stderr.on("data", (data) => {
  error += data.toString();
});

Waiting for exit

To wait for the child process to close and check the exit code, you can use the close event of the child process.

const exitCode = await new Promise((resolve, reject) => {
  child.on("close", resolve);
});

if (exitCode) {
  throw new Error(`subprocess error exit ${exitCode}, ${error}`);
}

Driving a process to completion

Combining the two methods, we can drive any child process to completion and get its output.

async function driveChild(child) {
  let output = "";
  child.stdout.on("data", (data) => {
    output += data.toString();
  });

  let error = "";
  child.stderr.on("data", (data) => {
    error += data.toString();
  });

  const exitCode = await new Promise((resolve, reject) => {
    child.on("close", resolve);
  });

  if (exitCode) {
    throw new Error(`subprocess error exit ${exitCode}, ${error}`);
  }

  return output;
}

export async function test() {
  const child = spawn("echo", ["Hello, world!"]);
  const result = await driveChild(child);
  return result;
}

Executing within in a shell

You can use the shell: true or shell: '/shell/path' options to execute the command in a shell.

import { spawn } from "child_process";

export async function test() {
  const child = spawn("echo", ["Hello, world!"], { shell: true });
  const result = await driveChild(child);
  return result;
}