index.js

#!/usr/bin/env node

const fs = require('fs');
const split2 = require('split2');

let port = Number(process.env.START_PORT);
const list =[];

process.stdin.pipe(split2())
  .on('data', p => list.push(p))
  .on('end', function() {
    const json = JSON.stringify({
      ip: process.env.PUBLIC_IP,
      list: list.reverse().map((password, index) => {
        if(index !== 0) {
          port = port + 2;
        }
        return {port, password};
      })
    });
    fs.writeFileSync('./config.json', json);
    console.log('Generated config.json');
  });

package.json

{
  "name": "generate-config-file.js",
  "version": "1.0.0",
  "description": "",
  "bin": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "MIT",
  "dependencies": {
    "split2": "^3.1.1"
  }
}