I am still trying to grasp the finer points of how I can run a linux or windows shell command and capture output within node.js; ultimately, I want to do something like this...

//pseudocode

output = run_command(cmd, args)

The important piece is that output must be available to a globally scoped variable (or object). I tried the following function, but for some reason, I get undefined printed to the console...

function run_cmd(cmd, args, cb) {

  var spawn = require('child_process').spawn

  var child = spawn(cmd, args);

  var me = this;

  child.stdout.on('data', function(me, data) {

    cb(me, data);

  });

}

foo = new run_cmd('dir', ['/B'], function (me, data){me.stdout=data;});

console.log(foo.stdout);  // yields undefined <------

I'm having trouble understanding where the code breaks above... a very simple prototype of that model works...

function try_this(cmd, cb) {

  var me = this;

  cb(me, cmd)

}

bar = new try_this('guacamole', function (me, cmd){me.output=cmd;})

console.log(bar.output); // yields guacamole <----

Can someone help me understand why try_this() works, and run_cmd() does not? FWIW, I need to use child_process.spawn, because child_process.exec has a 200KB buffer limit.

Final Resolution

I'm accepting James White's answer, but this is the exact code that worked for me...

function cmd_exec(cmd, args, cb_stdout, cb_end) {

  var spawn = require('child_process').spawn,

    child = spawn(cmd, args),

    me = this;

  me.exit = 0;  // Send a cb to set 1 when cmd exits

  me.stdout = ;

  child.stdout.on('data', function (data) { cb_stdout(me, data) });

  child.stdout.on('end', function () { cb_end(me) });

}

foo = new cmd_exec('netstat', ['-rn'], 

  function (me, data) {me.stdout += data.toString();},

  function (me) {me.exit = 1;}

);

function log_console() {

  console.log(foo.stdout);

}

setTimeout(

  // wait 0.25 seconds and print the output

  log_console,

250);