Exec : display stdout “live”

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 ? !

Thanks

Answer 1

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).

Answer 2

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);