Unable to get output from child process

Question

So, I have a simple app (I have written) which writes to stdout.

When I run it by itself, the output is being printed fine.

Now, when I spawn the process with node... nothing happens (apart from a message saying the process has finished)

Here's my code:

var spawn = require('child_process').spawn;
helper = spawn("myApp", []);
helper.stdout.on('data', function(data) { 
    console.log("GOT: " + data);
});
helper.stdout.on('end', function(data) {
    console.log("FINISHED: " + data);
});
helper.on('exit', function(code) {
    console.log("CLOSED!");
});

And here's the output:

FINISHED: undefined
CLOSED!

Yep, just that.

What's going on? Am I missing something?

When I change the spawn() to spawn("sh", ["-c", "echo hello world"]) it works fine for me, though I get the "close" event before the data. — Pointy
– Pointy, Commented Sep 13, 2015 at 0:07
Well, the end even does fire. The stdout.on('data',...) part isn't... — Dr.Kameleon
– Dr.Kameleon, Commented Sep 13, 2015 at 0:09
Are you sure that your application code properly flushes its output buffers? (Not super-likely to be the case, but the child process stuff is pretty darned close to a raw wrapper around the underlying system calls.) — Pointy
– Pointy, Commented Sep 13, 2015 at 0:10
Hmm... Am I? That's a good question. It's an Objective-C terminal app, fprintfing to stdout... Let me double-check. — Dr.Kameleon
– Dr.Kameleon, Commented Sep 13, 2015 at 0:12

Pointy · Accepted Answer · 2015-09-13 00:24:22Z

2

Make sure your stdio output buffers are being flushed in your application:

  fflush(stdout); // or something like that

Output straight to the tty has less buffering than output to a pipe.

answered Sep 13, 2015 at 0:24

Pointy

415k62 gold badges600 silver badges631 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Pointy Over a year ago

@Dr.Kameleon no problem - fun opportunity to use some stuff I had forgotten I even knew :)

Dr.Kameleon Over a year ago

The trouble is that I had forgotten too. I guess there are times like this when it all comes back up... haha.

Collectives™ on Stack Overflow

Unable to get output from child process

1 Answer 1

2 Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Related