Node.js Child Processes

Node.js Child Processes: Executing Shell Commands & Parallel System Tasks

The node:child_process module enables Node.js to spawn sub-processes, execute external terminal commands, run shell scripts, and communicate with child Node.js instances via Inter-Process Communication (IPC).

Child Process Creation Methods (exec, spawn, fork)

flowchart TD
    A["node:child_process"] --> B["exec(): Buffer output string (small commands)"]
    A --> C["spawn(): Stream large stdout/stderr chunks continuously"]
    A --> D["fork(): Spawn Node.js process with dedicated IPC channel"]

Practical Code Example

import { spawn, exec, fork } from 'node:child_process';
import { promisify } from 'node:util';

const execAsync = promisify(exec);

// 1. Using exec for quick CLI execution
async function runQuickCommand() {
    try {
        const { stdout, stderr } = await execAsync('node -v');
        console.log('Installed Node Version:', stdout.trim());
    } catch (err) {
        console.error('Command Execution Failed:', err);
    }
}

// 2. Using spawn for continuous stream processing
function runStreamedProcess() {
    const ls = spawn('ping', ['127.0.0.1']);

    ls.stdout.on('data', (data) => {
        console.log(`[Spawn Output]: ${data.toString().trim()}`);
    });

    ls.stderr.on('data', (data) => {
        console.error(`[Spawn Error]: ${data}`);
    });

    ls.on('close', (code) => {
        console.log(`Child process exited with code ${code}`);
    });
}

runQuickCommand();
runStreamedProcess();

Best Practices & Gotchas

• Beware of Buffer Limits in exec(): exec() buffers complete output in memory (default 1MB maxBuffer); use spawn() when commands produce large outputs to prevent memory overflow crashes.
• Prevent Command Injection Vulnerabilities: Never pass unsanitized user inputs directly into exec(); use spawn() with arguments passed as an array.
• Use fork() for Node Background Sub-Processes: Use child_process.fork() when spawning another Node.js script to get a built-in IPC channel (process.send()).

Self-Check Challenge

Which child process method is best suited for executing a child process that streams a 5GB video processing pipeline?