Introduction to child-process-promise

The child-process-promise library is a powerful and efficient
tool for managing child processes in Node.js applications. It provides
a promise-based approach to handling asynchronous child processes which
can significantly simplify your code and improve readability.

Below, we will explore a variety of useful APIs provided by the
child-process-promise library, along with code snippets and
an app example to demonstrate these capabilities.

Basic Usage of child-process-promise

The exec API allows you to execute a shell command and
returns a promise which resolves with the command’s stdout and stderr.

  const { exec } = require('child-process-promise');
  
  exec('ls')
    .then(result => {
      console.log('stdout:', result.stdout);
      console.log('stderr:', result.stderr);
    })
    .catch(err => {
      console.error('ERROR:', err);
    });

fork API

The fork API is used to spawn a new Node.js process.

  const { fork } = require('child-process-promise');
  
  const child = fork('script.js');
  
  child.on('message', message => {
    console.log('Message from child:', message);
  });
  
  child.send('Hello from parent');

spawn API

The spawn API is suitable for executing a new process with
a given set of arguments.

  const { spawn } = require('child-process-promise');
  
  spawn('echo', ['Hello, World!'])
    .then(result => {
      console.log('stdout:', result.stdout.toString());
      console.log('stderr:', result.stderr.toString());
    })
    .catch(err => {
      console.error('ERROR:', err);
    });

An Example Application

Assembling these APIs, we can build an application that utilizes child
processes for various tasks.

  const { exec, fork, spawn } = require('child-process-promise');
  
  // Example of exec
  exec('node --version')
    .then(result => {
      console.log('Node version:', result.stdout.trim());
    })
    .catch(err => {
      console.error('ERROR:', err);
    });

  // Example of fork
  const child = fork('childTask.js');
  child.on('message', message => {
    console.log('Message from child:', message);
  });
  child.send('Start child task');

  // Example of spawn
  const process = spawn('ls', ['-lh', '/usr']);
  process.childProcess.stdout.on('data', data => {
    console.log(`stdout: ${data}`);
  });
  process.childProcess.stderr.on('data', data => {
    console.error(`stderr: ${data}`);
  });
  process.then(() => {
    console.log('Process complete!');
  }).catch(err => {
    console.error('Process error:', err);
  });

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