gistfile1.js

var http = require('http');

var sites = [
  {
    hosts: [
      'something.com',
      'www.something.com'
    ],
    directory: 'something_public'
  },

  {
    hosts: [
      'somethingelse.com',
      'www.somethingelse.com'
    ],
    directory: 'somethingelse_public'
  }
];

var server = http.createServer(function(req, res) {
  var result = sites.map(function(site) {
    // Return false if the host isn't in this site.
    if (!req.headers.host ||
        !~site.hosts.indexOf(req.headers.host)) return false;

    // Return true if it is.
    return true;
  });

  if (!~result.indexOf(true)) {
    res.writeHead(404);
    return res.end("Couldn't find the requested site.");
  }

  /*
    Handle the rest of the stuff here.

    For example:
  */
  var site = sites[result.indexOf(true)];

  res.writeHead(200);
  res.end("Serve directory: " + site.directory + "\n");
});

server.listen(8080);

gistfile2.txt

curl localhost:8080 -H "Host: something.com"
curl localhost:8080 -H "Host: www.something.com"
curl localhost:8080 -H "Host: somethingelse.com"
curl localhost:8080 -H "Host: www.somethingelse.com"