readlineSync

Synchronous Readline for interactively running.
The interface is used with process.stdin and process.stdout in order to accept user input.

Example

var readlineSync = require('readline-sync');

var userName = readlineSync.question('May I have your name? :'); // Wait for user's response.
var favFood = readlineSync.question('Hi ' + userName + '! What is your favorite food? :');

console.log('Oh, ' + userName + ' likes ' + favFood + '!');

May I have your name? :AnSeki
Hi AnSeki! What is your favorite food? :chocolate
Oh, AnSeki likes chocolate!

Installation

npm install readline-sync

Methods

question

answer = readlineSync.question([query[, options]])

Displays the query to the user, and then returns the user's response after it has been typed.
You can specify options. (see Options)

The query may be string, or may not be (e.g. number, Date, Object, etc.). This is converted to string (i.e. toString method is called) before it is displayed every time.

prompt

input = readlineSync.prompt([options])

Displays the current prompt (See setPrompt method) to the user, and then returns the user's response after it has been typed.
You can specify options. (see Options)

setPrompt

currentPrompt = readlineSync.setPrompt([newPrompt])

Sets the prompt, for example when you run node on the command line, you see > , which is node's prompt. (See prompt method)

The newPrompt may be string, or may not be (e.g. number, Date, Object, etc.). This is converted to string (i.e. toString method is called) before it is displayed every time.
For example, [foo-directory]# like a bash shell that show the current directory.

// Simple Object that has toString method.
readlineSync.setPrompt({
  toString: function() {
    return '[' + require('path').basename(process.cwd()) + ']# '; // Get and show current directory.
  }
})

setEncoding

currentEncoding = readlineSync.setEncoding([newEncoding])

Set the encoding method of input (user's response) and output (prompt method and question method). Defaults to 'utf8'.

setPrint

readlineSync.setPrint([callback])

The specified callback Function is called when any outputs (prompt method and question method). Defaults to undefined.
The callback is given two arguments the output text and encoding.

For example, this is used to pass plain texts to the Logger, when texts are colored.

var readlineSync = require('readline-sync'),
  user, pw, command;
require('colors');

readlineSync.setPrint(function(display, encoding) {
  logger.log(display.stripColors); // Remove control characters.
});

console.log('Your account required.'.grey);
user = readlineSync.question('USER NAME'.white.inverse + ': ');
pw = readlineSync.question('PASSWORD'.white.inverse + ': ', {noEchoBack: true});
// Authorization ...
console.log(('Welcome, ' + user + '!').green.bold);

readlineSync.setPrompt('> '.bold.red);
command = readlineSync.prompt();

Options

An options Object can be specified to prompt method and question method. This Object can have following properties.

noEchoBack

Type: Boolean
Default: false

If true is specified, echo back is avoided. It is used to hide the secret text (e.g. password) which is typed by user on screen.
For example:

password = readlineSync.question('PASSWORD :', {noEchoBack: true});
console.log('Login ...');

The typed text is not shown on screen.

PASSWORD :
Login ...

noTrim

Type: Boolean
Default: false

By default, the leading and trailing white spaces are removed from typed text. If true is specified, those are not removed.

With Task Runner

The easy way to control the flow of task runner by the user's response:

• Grunt plugin: grunt-confirm
• gulp plugin: gulp-confirm

If you want to control the flow of task runner (e.g. Grunt), call readlineSync in a task callback that is called by task runner. Then the flow of tasks is paused and it is controlled by user.

Example: by using grunt-task-helper

$ grunt
Running "fileCopy" task
Files already exist:
  file-a.png
  file-b.js
Overwrite? (y/n) :y
file-a.png copied.
file-b.js copied.
Done.

Gruntfile.js

grunt.initConfig({
  taskHelper: {
    fileCopy: {
      options: {
        handlerByTask: function() {
          // Abort the task if user don't want.
          return readlineSync.question('Overwrite? (y/n) :')
            .toLowerCase() === 'y';
          // Or process.exit()
        },
        filesArray: []
      },
      ...
    }
  },
  copy: {
    fileCopy: {
      files: '<%= taskHelper.fileCopy.options.filesArray %>'
    }
  }
});

Note

Platforms

The your Node and OS may not support interactively reading from stdin. The stdin interfaces are different by platforms.
If in those platforms, an error is thrown.

try {
  answer = readlineSync.question('What is your favorite food? :');
} catch (e) {
  console.error(e);
  process.exit(1);
}

Reading by shell

readlineSync tries reading from stdin by shell if it is needed. And, it use "piping via files" for synchronous running.
As everyone knows, "piping via files" is no good. It blocks event loop and a process. It may make your script be slow.

Why did I choose it? :

• The best solution is child_process.execSync in core modules of Node. But it is not supported by current version.
• The good modules (native addon) for synchronous execution exist. But node-gyp can't compile those in some platforms or Node versions.
• I think that the security is important more than the speed. Some modules have problem about security. (Those don't protect data.) I think that the speed is not needed usually, because readlineSync is used while user types keys.

Someday, I may rewrite readlineSync to use child_process.execSync, or safety module.

Release History

• 2015-01-27 v0.5.0 Add options.noTrim.
• 2014-07-12 v0.4.0 Add options.noEchoBack.
• 2014-07-12 v0.3.0 Add setPrint().
• 2013-08-30 v0.2.0 Rewrite exporting methods.
• 2013-08-29 v0.1.0 Initial release.