Node Child Process

Last Updated : 27 Feb, 2025

NodeJS is designed to be single-threaded, but it provides a child_process module to create and manage child processes. This allows you to run system commands, execute other scripts, and perform computationally expensive tasks in parallel. The child process module is essential for tasks like running shell commands, spawning worker processes, and integrating with other programs.

What is a Child Process?

A child process is a separate process that is created and managed by the parent process (your NodeJS application). This allows you to run system commands (like listing files or checking memory usage)

Execute scripts (like Python, Bash, or another NodeJS script)
Perform CPU-intensive operations without blocking the main event loop
Create multiple processes that run in parallel (multi-threading in NodeJS)

The child_process module in NodeJS provides four methods to create child processes:

spawn: Launches a new process with a given command. It streams data between the parent and child processes.
exec: Runs a command in a shell and buffers the output. It’s useful for short-running commands.
execFile: Similar to exec, but it runs a specific executable file directly without a shell.
fork: A special case of spawn used to create NodeJS child processes. It enables communication between parent and child processes using send and on(‘message’).

Methods to Create Child Processes

1. spawn() method

The spawn() method launches a new process with a specified command and arguments, providing streams for input/output. It’s ideal for handling large outputs or long-running processes.

JavaScript

const { spawn } = require('child_process'); const child = spawn('ls', ['-lh', '/usr']);  child.stdout.on('data', (data) => {     console.log(`stdout: ${data}`); });  child.stderr.on('data', (data) => {     console.error(`stderr: ${data}`); });  child.on('close', (code) => {     console.log(`child process exited with code ${code}`); });

Output

Node child Process

In this example

spawn(‘ls’, [‘-lh’, ‘/usr’]): Executes the ls command with -lh and /usr as arguments.
child.stdout.on(‘data’, …): Listens for data from the standard output.
child.stderr.on(‘data’, …): Listens for data from the standard error.
child.on(‘close’, …): Listens for the close event, indicating the process has finished.

2. fork() method

The fork() method is a special case of spawn() used specifically for spawning new NodeJS processes. It establishes an IPC (Inter-Process Communication) channel between the parent and child processes, allowing them to communicate via message passing.

JavaScript

const { fork } = require('child_process');  const child = fork('child.js');  child.on('message', (message) => {   console.log(`Message from child: ${message}`); });  child.send('Hello from parent');

JavaScript

// Child.js  // Listen for messages from the parent process process.on('message', (message) => {   console.log(`Message from parent: ${message}`);    // Send a response back to the parent   process.send('Hello from child'); });

Output

Fork methode

In this example

fork(‘child.js’): Spawns a new NodeJS process running the child.js module.
child.on(‘message’, …): Listens for messages from the child process.
child.send(‘Hello from parent’): Sends a message to the child process.

3. exec() method

The exec() method runs a command in a shell and buffers the output, which is suitable for short-lived commands with small outputs.

JavaScript

const { exec } = require('child_process');  // Counts the number of directory in // current working directory exec('dir | find /c /v ""', (error, stdout, stderr) => {     if (error) {         console.error(`exec error: ${error}`);         return;     }     console.log(`stdout: No. of directories = ${stdout}`);     if (stderr != "")         console.error(`stderr: ${stderr}`); });

JavaScript

// child_process const child = spawn('cmd', ['/c', 'dir']);

Output

exec methdo

In this example

exec(‘ls -lh /usr’, …): Executes the ls command with -lh and /usr as arguments.
The callback receives error, stdout, and stderr as parameters.
Logs the standard output and error to the console.

4. execFile() method

The execFile() method runs an executable file directly without spawning a shell, making it more efficient than exec() for running binaries and scripts directly.

JavaScript

const { execFile } = require('child_process');  execFile('node', ['--version'], (error, stdout, stderr) => {     if (error) {         console.error(`execFile error: ${error}`);         return;     }     console.log(`stdout: ${stdout}`);     if (stderr) {         console.error(`stderr: ${stderr}`);     } });

execFile(‘node’, [‘–version’], …): Executes the NodeJS binary with the –version flag.
The callback receives error, stdout, and stderr as parameters.
Logs the standard output and error to the console.

Comparison of exec, execFile, spawn, and fork

Method	Use Shell?	Returns Output	Streaming	Use Cases
exec()	Yes	Buffers output	No	Small shell commands
execFile()	No	Buffers output	No	Running binary files
spawn()	Yes	No (streams instead)	Yes	Handling large outputs
fork()	No	Uses message passing	Yes	Running child NodeJS processes

Best Practices for Using Child Processes

Use exec() for simple shell commands (when output size is small).
Use execFile() for executing binary files (faster & safer).
Use spawn() for handling large data or real-time output streaming.
Use fork() for multi-processing and parallel execution in NodeJS.
Always handle errors properly (use stderr and error events).
Use asynchronous methods whenever possible to avoid blocking the event loop.

Node.js process.kill() Method

Shreyasi_Chakraborty

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Article Tags :

Node Child Process

What is a Child Process?

Methods to Create Child Processes

1. spawn() method

2. fork() method

3. exec() method

4. execFile() method

Comparison of exec, execFile, spawn, and fork

Best Practices for Using Child Processes

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