1. You can try netstat

    netstat -vanp tcp | grep 3000
   

2. For macOS El Capitan and newer (or if your netstat doesn't support -p), use lsof

    lsof -i tcp:3000 
   

3. For Centos 7 use:

    netstat -vanp --tcp | grep 3000
   

Standard Method (no library)

The arguments are stored in process.argv

Here are the node docs on handling command line args:

process.argv is an array containing the command line arguments. The first element will be 'node', the second element will be the name of the JavaScript file. The next elements will be any additional command line arguments.

// print process.argv
process.argv.forEach(function (val, index, array) {
  console.log(index + ': ' + val);
});

This will generate:

$ node process-2.js one two=three four
0: node
1: /Users/mjr/work/node/process-2.js
2: one
3: two=three
4: four