Node: Writable stream, to get data from file and write on another.

node-writable-stream.js

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

// Create interface with a reading stream
const myInterface = readline.createInterface({
  input: fs.createReadStream('shoppingList.txt')
});

// Create a write stream to custom file
const fileStream = fs.createWriteStream('shoppingResults.txt.');

// Design callback to output in writable file
const transformData = (line) => {
  fileStream.write(`They were out of: ${line}\n`);
}

// Output on each line read
myInterface.on('line', transformData);