readlineSync

Synchronous Readline for interactively running to have a conversation with the user via a console(TTY).

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]])

Display the query to the user, and then return the user's response after it has been typed and Enter key was pressed.
You can specify options (see Options). If the user inputs the secret text (e.g. password), you should consider noEchoBack option.

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.

prompt

input = readlineSync.prompt([options])

Display the current prompt (See setPrompt method) to the user, and then return the user's response after it has been typed and Enter key was pressed.
You can specify options (see Options). If the user inputs the secret text (e.g. password), you should consider noEchoBack option.

setPrompt

currentPrompt = readlineSync.setPrompt([newPrompt])

Set the prompt, for example when you run node on the command line, you see > , which is node's prompt. The default is '> '. (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.
  }
})

setPrint

readlineSync.setPrint([callback])

The specified callback Function is called when any outputs (prompt method and question method) are done. 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'),
  chalk = require('chalk'),
  user, pw, command;

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

console.log(chalk.black.bold.bgYellow('    Your Account    '));
user = readlineSync.question(chalk.gray.underline(' USER NAME ') + ' :');
pw = readlineSync.question(chalk.gray.underline(' PASSWORD  ') + ' :', {noEchoBack: true});
// Authorization ...
console.log(chalk.green('Welcome, ' + user + '!'));

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

• When you do the redirecting that like your-script > foo.log to record into a file, this is used to output conversation to the file. That is, the conversation isn't outputted to foo.log without this code.

var readlineSync = require('readline-sync');
readlineSync.setPrint(function(display, encoding) {
  console.log(display); // Output to STDOUT (foo.log)
});

setMask

currentMask = readlineSync.setMask([newMask])

Set the mask character that is shown instead of the secret text (e.g. password) when noEchoBack option is true. (See noEchoBack option.) The default is '*'. If you want to show nothing, specify ''. (But it might be not user friendly in some cases.)
Note: The some platforms might use '*' or '' always.

For example:

var readlineSync = require('readline-sync'),
  chalk = require('chalk'),
  secret;

readlineSync.setMask(chalk.magenta('\u2665'));
secret = readlineSync.question('Please whisper sweet words :', {noEchoBack: true});

setBufferSize

currentBufferSize = readlineSync.setBufferSize([newBufferSize])

When readlineSync reads from TTY directly (without reading by shell), a size newBufferSize buffer is used. Even if the user's response exceeds it, it's usually no problem, because the buffer is used repeatedly. But, some platforms's TTY might not accept user's response that exceeds it. And set an enough size. The default is 1024.

setEncoding

currentEncoding = readlineSync.setEncoding([newEncoding])

Set the encoding method of input (user's response) and output (prompt method and question method). The default is 'utf8'.

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, the secret text (e.g. password) which is typed by user on screen is hidden by the mask characters. (See setMask method)

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 TTY interfaces are different by platforms. If the platform doesn't support interactively reading from TTY, 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 TTY by shell if it is needed. And if the running Node doesn't support the Synchronous Process Execution (i.e. Node v0.10-), it uses "piping via files" for synchronous running.
As everyone knows, "piping via files" is no good. It blocks the event loop and a process. It may make your script be slow.

Why did I choose it? :

• 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.

Release History

• 2015-02-22 v0.6.0 Add setBufferSize().
• 2015-02-12 v0.5.5 Support the Synchronous Process Execution of Node v0.12(v0.11).
• 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.