Ruby subprocess with node.js

Question

I'm trying to launch a ruby instance as subprocess of my node program. In fact, everything is OK but I just can't interact with the ruby's STDIN and STDOUT. (of course the ruby program works in my terminal with my keyboard input)

So this is a simplified code that I want to get working ...

simpleproc.js

var util   = require('util'),
    spawn = require('child_process').spawn,
    ruby  = spawn('ruby', [__dirname + '/process.rb']);

ruby.stdout.on('data', function (data) {
  console.log('stdout: ' + data);
});

ruby.stderr.on('data', function (data) {
  console.log('stderr: ' + data);
});

ruby.on('exit', function (code) {
  console.log('child process exited with code ' + code);
});

ruby.stdin.write("ping\n");

process.rb

f = File.new("process.log", "w")
f.write "=== Hello! ===\n"
STDIN.each_line do |line|
   STDOUT.write line
   f.write line
end

What's wrong with it ? I've already managed to get an another process working... but here, there is no IO ! Nothing happens !

EDIT: I modified the ruby file to show that, with node, the file is only written with === Hello! ===\n inside. So we can say that, the ruby file is correctly launched but doesn't receive anything from node (I've tried to flush after the STDOUT.write but the do statement is never executed.

I tried using your example, but ruby seems to hang before it even creates that log file. Any ideas? stackoverflow.com/questions/6902641/… — Sjors Provoost
– Sjors Provoost, Commented Aug 1, 2011 at 18:25

michaelku · Accepted Answer · 2011-03-19 00:48:42Z

3

Try STDOUT.flush on the ruby side after STDOUT.write, as the output is being buffered.

answered Mar 19, 2011 at 0:48

michaelku

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3 Comments

ricard.robin Over a year ago

Sorry but it didn't work because the ruby STDIN, doesn't receive anything. If I try to write in a file in the do statement, nothing happens anyway. So, I can't see where the problem is. But that's maybe due to my node's version (master branch in the github repo).

michaelku Over a year ago

Maybe it's the version. Using node 0.4.2 and ruby 1.8.7 (Mac) your code works for me after I add a flush (silence without it). Writing to a file or to node from ruby should not make a difference.

ricard.robin Over a year ago

Oh boy ! In fact I wrote this ruby.stdin.write("ping"); in my own JS file. But thank you anyway, your answer was good because without the flush instruction, there was no way to get it working ! Thanks !

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