emfile.js

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

function create_path (basename, y, m, d, callback) {
    var path = [basename, y, m, d].join('/'), mkdir;
    mkdir = spawn('mkdir', ['-p', path], function (err, out, err_out) {
        if (err) throw err;
        callback(path, {stdout: out, stderr: err_out});
    });

    mkdir.on('exit', function (code) {
        if (code != '0') {
            throw 'mkdir -p ' + path + ' failed.';
        } else {
            callback(path);
        }
    });

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

for (var i = 0; i < 5; i++) {
    for (var j = 0; j < 5; j++) {
        for (var k = 0; k < 5; k++) {
            create_path('./tmp', i, j, k, function done (path) {
                console.log('Wrote', path);
            });
        }
    }
}

error.log

[7557]: node emfile.js

node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
Error: spawn EMFILE
    at errnoException (child_process.js:482:11)
    at ChildProcess.spawn (child_process.js:445:11)
    at child_process.js:343:9
    at create_path (/Users/josh/Dropbox/Documents/blog/emfile.js:6:13)
    at Object.<anonymous> (/Users/josh/Dropbox/Documents/blog/emfile.js:27:13)
    at Module._compile (module.js:441:26)
    at Object..js (module.js:459:10)
    at Module.load (module.js:348:31)
    at Function._load (module.js:308:12)
    at Array.0 (module.js:479:10)