Child Process in Node

In Node.js, child processes can be created to run external commands or scripts independently from the main process.

The "child_process" module provides the necessary functionalities for working with child processes.

Ways to create child process in node.js

spawn(): Launches a new process with the given command.
exec(): Executes a command in a shell and buffers the output.
execFile(): Similar to exec(), but executes a file directly instead of through a shell.
fork(): Used to spawn new Node.js processes.

Executing a Child Process with spawn() method:

The spawn function is used to spawn a new process and execute a command.

Example:

const { spawn } = require('child_process');

const childProcess = spawn('ls', ['-l', '-a']);

childProcess.stdout.on('data', (data) => {
  console.log(`Child Process Output: ${data}`);
});

childProcess.on('close', (code) => {
  console.log(`Child Process Exited with Code: ${code}`);
});

Executing a Child Process with exec() method:

The "exec" function is used to execute a command in a shell.

Example:

const { exec } = require('child_process');

exec('ls -l -a', (error, stdout, stderr) => {
  if (error) {
    console.error(`Error: ${error.message}`);
    return;
  }

  console.log(`Child Process Output: ${stdout}`);
});

Executing a Child Process with Promises:

The `promisify` utility from the `util` module can be used to convert callback-based functions to promise-based functions.

Note: "Util" Module is also pre-defined module inside Node Package Manager

const { promisify } = require('util');
const execAsync = promisify(require('child_process').exec);

async function runCommand() {
  try {
    const { stdout } = await execAsync('ls -l -a');
    console.log(`Child Process Output: ${stdout}`);
  } catch (error) {
    console.error(`Error: ${error.message}`);
  }
}

runCommand();

Communication between Parent and Child using fork() method:

The "fork" function is used to spawn a new Node.js process, and communication between the parent and child processes can be achieved through inter-process communication (IPC).

create file with name "parent.js" and paste the below code

Example:

const { fork } = require('child_process');

const childProcess = fork('child.js');

childProcess.on('message', (message) => {
  console.log(`Parent received message: ${message}`);
});

childProcess.send('Hello from parent!');

In the child process (child.js):

create file with name "child.js" and paste the below code.

Example:

process.on('message', (message) => {

  console.log(`Child received message: ${message}`);
  process.send('Hello from child!');

});

Run the code of parent process file: -> parent.js with command `node parent.js`

Output:

// terminal Console Output will be:
>
> node parent.js
Child received message: Hello from parent!
Parent received message: Hello from child!

<-- Process

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Child Process in Node

In Node.js, child processes can be created to run external commands or scripts independently from the main process.

The "child_process" module provides the necessary functionalities for working with child processes.

Ways to create child process in node.js

spawn(): Launches a new process with the given command.
exec(): Executes a command in a shell and buffers the output.
execFile(): Similar to exec(), but executes a file directly instead of through a shell.
fork(): Used to spawn new Node.js processes.

Executing a Child Process with spawn() method:

The spawn function is used to spawn a new process and execute a command.

Example:

const { spawn } = require('child_process');

const childProcess = spawn('ls', ['-l', '-a']);

childProcess.stdout.on('data', (data) => {
  console.log(`Child Process Output: ${data}`);
});

childProcess.on('close', (code) => {
  console.log(`Child Process Exited with Code: ${code}`);
});

Executing a Child Process with exec() method:

The "exec" function is used to execute a command in a shell.

Example:

const { exec } = require('child_process');

exec('ls -l -a', (error, stdout, stderr) => {
  if (error) {
    console.error(`Error: ${error.message}`);
    return;
  }

  console.log(`Child Process Output: ${stdout}`);
});

Executing a Child Process with Promises:

The `promisify` utility from the `util` module can be used to convert callback-based functions to promise-based functions.

Note: "Util" Module is also pre-defined module inside Node Package Manager

const { promisify } = require('util');
const execAsync = promisify(require('child_process').exec);

async function runCommand() {
  try {
    const { stdout } = await execAsync('ls -l -a');
    console.log(`Child Process Output: ${stdout}`);
  } catch (error) {
    console.error(`Error: ${error.message}`);
  }
}

runCommand();

Communication between Parent and Child using fork() method:

The "fork" function is used to spawn a new Node.js process, and communication between the parent and child processes can be achieved through inter-process communication (IPC).

create file with name "parent.js" and paste the below code

Example:

const { fork } = require('child_process');

const childProcess = fork('child.js');

childProcess.on('message', (message) => {
  console.log(`Parent received message: ${message}`);
});

childProcess.send('Hello from parent!');

In the child process (child.js):

create file with name "child.js" and paste the below code.

Example:

process.on('message', (message) => {

  console.log(`Child received message: ${message}`);
  process.send('Hello from child!');

});

Run the code of parent process file: -> parent.js with command `node parent.js`

Output:

// terminal Console Output will be:
>
> node parent.js
Child received message: Hello from parent!
Parent received message: Hello from child!

<-- Process

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