The child_process module provides several methods for spawning child processes from Node.js applications including exec, execFile, spawn, and fork. exec spawns a shell and runs a command, passing stdout and stderr to a callback. execFile is similar but spawns directly without a shell. spawn spawns a process and returns a ChildProcess object for sending/receiving messages. fork spawns a new Node.js process and allows sending messages between parent and child.

1. Node - Child Process
Jason

2. Child Process
● The child_process module provides the ability to spawn child processes in a
manner that is similar.
var child_process = require (‘child_process’);

3. Child Process
● exec
● spawn
● execFile
● fork

4. exec
spawns a shell and runs a command within that shell, passing the stdout and
stderr to a callback function when complete.
exec(command[, options][, callback])
var cp = require('child_process');
cp.exec('node -v', (err, stdout, stderr) => {
if(err){ return; }
console.log(stdout);
});

5. execFile
similar to child_process.exec() except that it spawns the command directly without
first spawning a shell.
execFile(file[, args][, options][, callback])
var cp = require('child_process');
cp.execFile('/bin/ls', ['-v'], (error, stdout, stderr) => {
if (error) { throw error; }
console.log(stdout);
});

6. exec VS execFile
var path = ";pwd";
child_process.exec('ls ' + path, (err, stdout, stderr)=> {
console.log(stdout);
});
var path = ".;pwd";
child_process.execFile('ls', ['-l', path], (err, stdout, stderr) => {
console.log(stdout)
});

7. spawn
spawn(command[, args][, options])
var cp = require('child_process');
var path = '.';
var ls = cp.spawn('ls', ['-l', path]);
ls.stdout.on('data', (data) => { ….. });
ls.stderr.on('data', (data) => { …. });
ls.on('close', (code) => { ….. });

8. exec VS spawn
exec ：default options
{
encoding: 'utf8',
timeout: 0,
maxBuffer: 200*1024,
killSignal: 'SIGTERM',
cwd: null,
env: null
}
spawn：default options
{
cwd: undefined,
env: process.env
}

9. fork
fork(modulePath[, args][, options])
● spawns a new Node.js process and invokes a specified module
● The returned ChildProcess will have an additional communication channel built-in that allows messages
to be passed back and forth between the parent and child.
fork('./child.js')
∣∣
spawn('node', ['./child.js'])

10. fork
fork(modulePath[, args][, options]) child.js
parent.js
var cp = require('child_process');
var n = cp.fork('./child.js');
n.on('message', (m) => {
console.log('parent got message:', m);
});
n.send({ hello: 'world' });
process.on('message', (m) => {
console.log('child got message:', m);
});
process.send({ foo: 'bar' });

11. Reference
Node child_process
https://nodejs.org/api/child_process.html