Invoke CGI from Express.js.

app.js

var express = require('express');
var cgi = require('./cgi');
app = express();

var script = __dirname + '/hello.cgi';
app.get('/', cgi(script, function (req, options) {
  options.env.USERNAME = 'Mr. User';
}));

app.use(function (err, req, res, next) {
  res.send(500, 'Error: ' + err.message);
});

app.listen(process.env.PORT || 3000);

cgi.js

var fs = require('fs');
var url = require('url');
var path = require('path');
var spawn = require('child_process').spawn;
var CGIParser = require('cgi/parser');

module.exports = function (cgiPath, callback) {
  return function (req, res, next) {
    try {
      var stat = fs.statSync(cgiPath);
      if (! stat.isFile() || (stat.mode & parseInt('111', 8)) == 0) {
        return next(new Error('cgi file\'s mode = ' + stat.mode));
      }
    } catch (err) {
      return next(err);
    }
    var parsedUrl = url.parse(req.url);
    var env = {
      REQUEST_METHOD: req.method,
      QUERY_STRING: parsedUrl.query || ''
    };
    if ('content-length' in req.headers) {
      env.CONTENT_LENGTH = req.headers['content-length'];
    }
    var options = { cwd: path.dirname(cgiPath), env: env };
    if (callback) callback(req, options);
    var proc = spawn(cgiPath, [], options);
    req.pipe(proc.stdin);
    var result = new CGIParser(proc.stdout);
    result.on('headers', function (headers) {
      headers.forEach(function (header) {
        if (header.key === 'Status') return;
        res.setHeader(header.key, header.value);
      });
      res.statusCode = parseInt(headers.status, 10) || 200;
      result.pipe(res);
    });
    proc.on('exit', function (code, signal) {
      if (code || signal) {
        next(new Error('cgi proc died: code = ' + code + ', signal = ' + signal));
      }
    });
    proc.stdout.on('end', function () {
      if (result) result.cleanup();
    });
  };
};

hello.cgi

#!/bin/sh

echo Status: 200
echo Content-Type: text/plain
echo
echo Hello, $USERNAME!

package.json

{
  "name": "express-cgi",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "start": "node app"
  },
  "dependencies": {
    "express": "*",
    "cgi": "*"
  }
}