Exec : display stdout "live"

Don't use exec. Use spawn which is an EventEmmiter object. Then you can listen to stdout/stderr events (spawn.stdout.on('data',callback..)) as they happen.

From NodeJS documentation:

var spawn = require('child_process').spawn,    ls    = spawn('ls', ['-lh', '/usr']);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('child process exited with code ' + code.toString());});

exec buffers the output and usually returns it when the command has finished executing.

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.