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What are the four main methods for creating a child process in Node.js, and how do they differ? How does inter-process communication (IPC) work between a parent process and a child created with fork()? 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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How would you pipe the output of one child process directly into the input of another, replicating a shell pipeline in Node.js?

Intermediate

Answer

Each child process's stdout and stdin are Node.js streams, so you can use .pipe() directly to connect one process's stdout to another's stdin, replicating a shell pipeline like 'cat file.txt | grep pattern' entirely within Node.js code, with all the usual stream backpressure handling applying automatically.
const { spawn } = require('node:child_process');

const cat = spawn('cat', ['large-file.txt']);
const grep = spawn('grep', ['error']);

cat.stdout.pipe(grep.stdin);
grep.stdout.pipe(process.stdout);
Real-world example A log-analysis script pipes a 'cat' process's output through a 'grep' child process to filter for error lines, then pipes that filtered output directly to the parent process's own stdout, replicating a familiar shell pipeline programmatically for use within a larger Node.js automation script.

Common follow-ups: How does backpressure propagate correctly through a multi-stage piped child process chain?;What happens to the downstream process if the upstream process is killed mid-pipeline?

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