Use stack introspection to determine the filename of a calling script.

stack1.js

// An example of how to use stack introspection to determine the
// filename of a calling script.
//
//     node stack1.js
//

function blah() {
  require('./stack2');
}

blah();

stack2.js

// See stack1.js

function peek(which) {
  try {
    // Throw a dummy error to capture a stack trace.
    throw new Error('peek');
  }
  catch (e) {
    // Split the stack trace into lines. Each line ends with a filename:
    //
    //     at method (file:line:column)
    //     ...
    //
    // If the filename is absolute (ignore "node.js") and isn't this
    // file, return it.
    var probe, trace = e.stack.split(/\n/);
    which = which || 0;
    for (var i = 0, l = trace.length; i < l; i++) {
      if ((probe = trace[i].match(/\((\/[^:]+):\d+:\d+\)$/))
          && probe[1] != __filename
          && --which < 0)
        return probe[1];
    }
    return undefined;
  }
}

console.log(peek());