Best way to accept command line inputs synchronously in nodejs?

The easiest way to do this, IMHO is showing "questions" to the user and waiting to his answers. Those questions can be always the same (a prompt like ">>") or maybe different (if you want to ask for some variables, for instance).

To show these questions you can use stdio. It is a module that simplifies standard input/output management, and one of its main features is precisely what you want:

var stdio = require('stdio');
stdio.question('What is your name?', function (err, name) {
    stdio.question('Are you male or female?', ['male', 'female'], function (err, sex) {
        console.log('Your name is "%s". You are "%s"', name, sex);
    });
});

If you run the previous code you'll se something like this:

What is your name?: John
Are you male or female? [male/female]: female
Your name is "john". You are "female"

stdio includes support for retries if you specify a group of possible answers. Otherwise users will be able to write whatever they want.

PD: I'm the stdio creator. :-)

Depending on your specific needs, you could create your own REPL.

http://nodejs.org/api/repl.html

Just call repl.start() with options for prompt, and use your own custom eval and writer callbacks.

repl.start({
    prompt: 'Enter value: ',
    eval: function (cmd, context, filename, callback) {
         // Do something
        callback(/* return value goes here */); 
    },
    writer: function (data) {
        // echo out data to the console here
    }
});