Question

I have this simple script :

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

exec('coffee -cw my_file.coffee', function(error, stdout, stderr) {
    console.log(stdout);
});

where I simply execute a command to compile a coffee-script file. But stdout never get displayed in the console, because the command never ends (because of the -w option of coffee).
If I execute the command directly from the console I get message like this :

18:05:59 - compiled my_file.coffee

My question is : is it possible to display these messages with the node.js exec ? If yes how ? !

Answer 1

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.