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child_process

Spawn Other Programs From Node

child_process

Run shell commands or other programs from Node. spawn, exec, fork — three flavors.

4 min read Level 2/5 #nodejs#child-process#shell
What you'll learn
  • Use spawn for streaming output
  • Use exec for short commands
  • Use fork for spawning Node sub-processes

Sometimes Node needs to run another program — invoke git, shell out to ffmpeg, or fork a sub-process. That’s node:child_process.

exec — Short Commands

Returns the entire stdout/stderr at once:

import { exec } from "node:child_process";
import { promisify } from "node:util";

const run = promisify(exec);

const { stdout } = await run("git rev-parse HEAD");
console.log("commit:", stdout.trim());

Use for: one-off commands with small output. Don’t use with untrusted input — exec runs through a shell.

spawn — Streaming

For long-running processes or big output:

import { spawn } from "node:child_process";

const ls = spawn("ls", ["-la", "."]);

ls.stdout.on("data", (chunk) => process.stdout.write(chunk));
ls.stderr.on("data", (chunk) => process.stderr.write(chunk));

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

stdout/stderr are streams. Memory stays low even for huge output. Arguments are passed as an array — no shell injection risk.

execFile — Like exec, Safer

Same as exec but bypasses the shell. Pass args as an array:

import { execFile } from "node:child_process";
import { promisify } from "node:util";

const run = promisify(execFile);
const { stdout } = await run("git", ["log", "--oneline", "-5"]);

Prefer this over exec when you can.

fork — Node Sub-process

A specialized spawn for Node scripts, with IPC:

// main.mjs
import { fork } from "node:child_process";

const child = fork("./worker.mjs");
child.send({ task: "do thing" });
child.on("message", (msg) => console.log("child says", msg));
// worker.mjs
process.on("message", (msg) => {
  process.send({ result: 42 });
});

Use when you want process-level isolation that worker_threads doesn’t provide (separate V8 heap, separate event loop).

Choosing

ToolUse for
execQuick shell commands, small output
execFileSame, but safer (no shell)
spawnBig or streaming output
forkSpawn another Node script with IPC
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