How to live stream output from ruby script using child_process.spawn

Question

From what I understand, this should work, but no luck for me so far. Posting this question hoping I'm doing something really silly. I have:

hello.rb

#!/usr/bin/env ruby

3.times do
  puts 'hello'
  sleep 1
end

tail.js

var cp = require('child_process');
var tail = cp.spawn('./hello.rb');

tail.stdout.pipe(process.stdout);

/* Also tried this: */
tail.stdout.on('data', function(data) {
  console.log(data.toString())
});

hello.rb is executable.

When I run node tail.js, 3 hellos are printed to stdout, but after, the loop completes. You can verify this by changing 3.times to just loop for an infinite loop and seeing nothing in stdout. The infinite loop case is actually what I'm attempting to figure out how to do.

What am I doing wrong?

mscdex · Accepted Answer · 2014-04-11 00:24:37Z

1

You should try either adding $stdout.flush after your puts or by setting $stdout.sync = true at the beginning of your ruby script.

answered Apr 11, 2014 at 0:24

mscdex

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3 Comments

mehulkar Over a year ago

That worked, than you! Could you add a little bit about what that does?

mehulkar Over a year ago

I also edited the question title/tags to reflect that this had more to do with ruby than child_process or node.

mscdex Over a year ago

$stdout.flush flushes the current stdout buffer since writing to stdout is asynchronous by default. $stdout.sync = true switches to synchronous stdout output, which disables the stdout buffer and ensures that each write is flushed before continuing execution.

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