readline

What is readline?

The readline npm package is a core Node.js module that provides an interface for reading data from a Readable stream (like process.stdin) one line at a time. It is particularly useful for creating command-line interfaces and reading large files line by line.

What are readline's main functionalities?

Reading Input from stdin

This code sets up a readline interface to read user input from the standard input (stdin). It asks the user 'What is your name?' and prints a greeting with the user's input.

const readline = require('readline');
const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});
rl.question('What is your name? ', (answer) => {
  console.log(`Hello, ${answer}!`);
  rl.close();
});

Reading a File Line by Line

This example demonstrates how to use readline to read a file line by line. It creates a readline interface with a file stream as input and logs each line to the console as it is read.

const fs = require('fs');
const readline = require('readline');
const rl = readline.createInterface({
  input: fs.createReadStream('file.txt'),
  output: process.stdout,
  terminal: false
});
rl.on('line', (line) => {
  console.log(line);
});

Other packages similar to readline

readline-sync

readline-sync is an npm package that provides synchronous readline capabilities. Unlike the asynchronous nature of readline, readline-sync blocks the event loop until input is received. This is useful for CLI applications where synchronous operations are preferred.

inquirer

Inquirer.js is a powerful library for building interactive command-line interfaces. It offers more features than readline, such as checkboxes, lists, confirmations, and more. It is more suitable for complex CLI applications that require more than just line-by-line input.

README

readline

Read a file line by line.

Install

Important. In node 10 there is a core module named readline. Please use linebyline instead, it is the same module just renamed:

Npm linebyline

npm install linebyline

Test

npm install .
npm test

What's this?

Simple streaming readline module for NodeJS. Reads a file and buffer new lines emitting a line event for each line.

Usage

  var readline = require('linebyline'),
      rl = readline('./somefile.txt');
  rl.on('line', function(line) {
    // do something with the line of text
  })
  .on('error', function(e) {
    // something went wrong
  });

License

BSD © Craig Brookes