Bdtjtk

exec will also return a ChildProcess object that is an EventEmitter.

var exec = require('child_process').exec;

var coffeeProcess = exec('coffee -cw my_file.coffee');



coffeeProcess.stdout.on('data', function(data) {

    console.log(data); 

});

OR pipe the child process's stdout to the main stdout.

coffeeProcess.stdout.pipe(process.stdout);

OR inherit stdio using spawn

spawn('coffee -cw my_file.coffee', { stdio: 'inherit' });

There are already several answers however none of them mention the best (and easiest) way to do this, which is using spawn and the { stdio: 'inherit' } option. It seems to produce the most accurate output, for example when displaying the progress information from a git clone.

Simply do this:

var spawn = require('child_process').spawn;



spawn('coffee', ['-cw', 'my_file.coffee'], { stdio: 'inherit' });

Credit to @MorganTouvereyQuilling for pointing this out in this comment.

I'd just like to add that one small issue with outputting the buffer strings from a spawned process with console.log() is that it adds newlines, which can spread your spawned process output over additional lines. If you output stdout or stderr with process.stdout.write() instead of console.log(), then you'll get the console output from the spawned process 'as is'.

I saw that solution here:
Node.js: printing to console without a trailing newline?

Hope that helps someone using the solution above (which is a great one for live output, even if it is from the documentation).

Inspired by Nathanael Smith's answer and Eric Freese's comment, it could be as simple as:

var exec = require('child_process').exec;

exec('coffee -cw my_file.coffee').stdout.pipe(process.stdout);

After reviewing all the other answers, I ended up with this:

function oldSchoolMakeBuild(cb) {

    var makeProcess = exec('make -C ./oldSchoolMakeBuild',

         function (error, stdout, stderr) {

             stderr && console.error(stderr);

             cb(error);

        });

    makeProcess.stdout.on('data', function(data) {

        process.stdout.write('oldSchoolMakeBuild: '+ data);

    });

}

Sometimes data will be multiple lines, so the oldSchoolMakeBuild header will appear once for multiple lines. But this didn't bother me enough to change it.

I have found it helpful to add a custom exec script to my utilities that does this.

utilities.js

const { exec } = require('child_process')



module.exports.exec = (command) => {

  const process = exec(command)



  process.stdout.on('data', (data) => {

    console.log('stdout: ' + data.toString())

  })



  process.stderr.on('data', (data) => {

    console.log('stderr: ' + data.toString())

  })



  process.on('exit', (code) => {

    console.log('child process exited with code ' + code.toString())

  })

}

app.js

const { exec } = require('./utilities.js)



exec('coffee -cw my_file.coffee')

child_process.spawn returns an object with stdout and stderr streams.
You can tap on the stdout stream to read data that the child process sends back to Node. stdout being a stream has the "data", "end", and other events that streams have. spawn is best used to when you want the child process to return a large amount of data to Node - image processing, reading binary data etc.

so you can solve your problem using child_process.spawn as used below.

var spawn = require('child_process').spawn,

ls = spawn('coffee -cw my_file.coffee');



ls.stdout.on('data', function (data) {

  console.log('stdout: ' + data.toString());

});



ls.stderr.on('data', function (data) {

  console.log('stderr: ' + data.toString());

});



ls.on('exit', function (code) {

  console.log('code ' + code.toString());

});