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How does inter-process communication (IPC) work between a parent process and a child created with fork()? How would you pipe the output of one child process directly into the input of another, replicating a shell pipeline in Node.js? How do you handle a child process that hangs or never terminates, and what's the correct way to enforce a timeout? What is the 'detached' option when spawning a child process, and when would you use it?
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What are the four main methods for creating a child process in Node.js, and how do they differ?

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Answer

spawn() launches a command and streams its stdout/stderr incrementally, suited for long-running processes or large output. exec() runs a command through a shell and buffers its entire output into a callback, convenient for short commands with small output but risky for large output (memory) and shell-injection if input isn't sanitized. execFile() is like exec() but runs an executable directly without a shell, avoiding shell-injection risk. fork() is a specialized spawn specifically for running another Node.js script as a child process, automatically setting up an IPC channel for message passing.
const { spawn, exec, execFile, fork } = require('node:child_process');

spawn('ls', ['-la']); // streaming output
exec('ls -la', (err, stdout) => console.log(stdout)); // buffered, via shell
execFile('ls', ['-la'], (err, stdout) => console.log(stdout)); // buffered, no shell
fork('./worker-script.js'); // another Node.js process, with IPC built in
Real-world example A CI tool uses spawn() to stream a long-running build command's output line by line to the console in real time, while a smaller utility script uses execFile() to safely run a fixed executable with user-supplied arguments, avoiding the shell-injection risk that exec() would introduce with unsanitized input.

Common follow-ups: Why is exec() considered risky when any part of the command string comes from user input?;What's the memory implication of exec()'s output-buffering behavior for a command producing gigabytes of output?

Security;CLI Tools & Scripting with Node.js
All 5 Child Processes & Process Management questions