readlineSync

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

readlineSync tries to let your script have a conversation with the user via a console, even when the input/output stream is redirected like your-script <foo.dat >bar.log.

• Simple case:

var readlineSync = require('readline-sync');
 
// Wait for user's response.
var userName = readlineSync.question('May I have your name? ');
console.log('Hi ' + userName + '!');
 
// Handle the secret text (e.g. password).
var favFood = readlineSync.question('What is your favorite food? ', {
  hideEchoBack: true // The typed text on screen is hidden by `*` (default).
});
console.log('Oh, ' + userName + ' loves ' + favFood + '!');

May I have your name? CookieMonster
Hi CookieMonster!
What is your favorite food? ****
Oh, CookieMonster loves tofu!

• Get the user's response by a single key without the Enter key:

var readlineSync = require('readline-sync');
if (readlineSync.keyInYN('Do you want this module?')) {
  // 'Y' key was pressed.
  console.log('Installing now...');
  // Do something...
} else {
  // Another key was pressed.
  console.log('Searching another...');
  // Do something...
}

• Let the user choose an item from a list:

var readlineSync = require('readline-sync'),
  animals = ['Lion', 'Elephant', 'Crocodile', 'Giraffe', 'Hippo'],
  index = readlineSync.keyInSelect(animals, 'Which animal?');
console.log('Ok, ' + animals[index] + ' goes to your room.');

[1] Lion
[2] Elephant
[3] Crocodile
[4] Giraffe
[5] Hippo
[0] CANCEL
 
Which animal? [1...5 / 0]: 2
Ok, Elephant goes to your room.

• An UI like the Range Slider:
  (Press Z or X key to change a value, and Space Bar to exit)

var readlineSync = require('readline-sync'),
  MAX = 60, MIN = 0, value = 30, key;
console.log('\n\n' + (new Array(20)).join(' ') +
  '[Z] <- -> [X]  FIX: [SPACE]\n');
while (true) {
  console.log('\x1B[1A\x1B[K|' +
    (new Array(value + 1)).join('-') + 'O' +
    (new Array(MAX - value + 1)).join('-') + '| ' + value);
  key = readlineSync.keyIn('',
    {hideEchoBack: true, mask: '', limit: 'zx '});
  if (key === 'z') { if (value > MIN) { value--; } }
  else if (key === 'x') { if (value < MAX) { value++; } }
  else { break; }
}
console.log('\nA value the user requested: ' + value);

• Handle the commands repeatedly, such as the shell interface:

readlineSync.promptCLLoop({
  add: function(target, into) {
    console.log(target + ' is added into ' + into + '.');
    // Do something...
  },
  remove: function(target) {
    console.log(target + ' is removed.');
    // Do something...
  },
  bye: function() { return true; }
});
console.log('Exited');

> add pic01.png archive
pic01.png is added into archive.
> delete pic01.png
Requested command is not available.
> remove pic01.png
pic01.png is removed.
> bye
Exited

Installation

npm install readline-sync

Quick Start

How does the user input?

• Type a reply to a question, and press the Enter key (A)
• Type a keyword like a command in prompt, and press the Enter key (B)
• Press a single key without the Enter key (C)

(A) What does the user input?

• E-mail address
• New password
• Integer number
• Floating-point number
• Local file/directory path
• Others

(B) What does your script do?

• Receive a parsed command-name and arguments
• Receive an input repeatedly
• Receive a parsed command-name and arguments repeatedly
• Receive an input with prompt that is similar to that of the user's shell
• Others

(C) What does the user do?

• Say "Yes" or "No"
• Say "Yes" or "No" explicitly
• Make the running of script continue when ready
• Choose an item from a list
• Others

Basic Methods

These are used to control details of the behavior. It is recommended to use the Utility Methods instead of Basic Methods if it satisfy your request.

question

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

Display a query to the user if it's specified, and then return the input from the user after it has been typed and the Enter key was pressed.
You can specify an options (see Basic Options) to control the behavior (e.g. refusing unexpected input, avoiding trimming white spaces, etc.). If you let the user input the secret text (e.g. password), you should consider hideEchoBack option.

The query may be string, or may not be (e.g. number, Date, Object, etc.). It is converted to string (i.e. toString method is called) before it is displayed. (see Note also)
It can include the placeholders.

For example:

program = readlineSync.question('Which program starts do you want? ', {
  defaultInput: 'firefox'
});

prompt

input = readlineSync.prompt([options])

Display a prompt-sign (see prompt option) to the user, and then return the input from the user after it has been typed and the Enter key was pressed.
You can specify an options (see Basic Options) to control the behavior (e.g. refusing unexpected input, avoiding trimming white spaces, etc.).

For example:

while (true) {
  command = readlineSync.prompt();
  // Do something...
}

keyIn

pressedKey = readlineSync.keyIn([query[, options]])

Display a query to the user if it's specified, and then return a character as a key immediately it was pressed by the user, without pressing the Enter key. Note that the user has no chance to change the input.
You can specify an options (see Basic Options) to control the behavior (e.g. ignoring keys except some keys, checking target key, etc.).

The query is handled the same as that of the question method.

For example:

menuId = readlineSync.keyIn('Hit 1...5 key: ', {limit: '$<1-5>'});

setDefaultOptions

currentDefaultOptions = readlineSync.setDefaultOptions([newDefaultOptions])

Change the Default Options to the values of properties of newDefaultOptions Object.
All it takes is to specify options that you want change, because unspecified options are not updated.

Basic Options

prompt, hideEchoBack, mask, limit, limitMessage, defaultInput, trueValue, falseValue, caseSensitive, keepWhitespace, encoding, bufferSize, print, history, cd

An options Object can be specified to the methods to control the behavior of readlineSync. The options that were not specified to the methods are got from the Default Options. You can change the Default Options by setDefaultOptions method anytime, and it is kept until a current process is exited.
Specify the options that are often used to the Default Options, and specify temporary options to the methods.

For example:

readlineSync.setDefaultOptions({limit: ['green', 'yellow', 'red']});
a1 = readlineSync.question('Which color of signal? '); // Input is limited to 3 things.
a2 = readlineSync.question('Which color of signal? '); // It's limited yet.
a3 = readlineSync.question('What is your favorite color? ', {limit: null}); // It's unlimited temporarily.
a4 = readlineSync.question('Which color of signal? '); // It's limited again.
readlineSync.setDefaultOptions({limit: ['beef', 'chicken']});
a5 = readlineSync.question('Beef or Chicken? ');        // Input is limited to new 2 things.
a6 = readlineSync.question('And you? ');                // It's limited to 2 things yet.

The Object as options can have following properties.

prompt

For prompt* methods only
Type: string or others
Default: '> '

Set the prompt-sign that is displayed to the user by prompt* methods. For example you see > that is Node.js's prompt-sign when you run node on the command line.
This may be string, or may not be (e.g. number, Date, Object, etc.). It is converted to string every time (i.e. toString method is called) before it is displayed. (see Note also)
It can include the placeholders.

For example:

readlineSync.setDefaultOptions({prompt: '$ '});

// Display the memory usage always.
readlineSync.setDefaultOptions({
  prompt: { // Simple Object that has toString method.
    toString: function() {
      var rss = process.memoryUsage().rss;
      return '[' + (rss > 1024 ? Math.round(rss / 1024) + 'k' : rss) + 'b]$ ';
    }
  }
});

[13148kb]$ foo
[13160kb]$ bar
[13200kb]$

hideEchoBack

Type: boolean
Default: false

If true is specified, hide the secret text (e.g. password) which is typed by user on screen by the mask characters (see mask option).

For example:

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

PASSWORD: ********
Login ...

mask

Type: string
Default: '*'

Set the mask characters that are shown instead of the secret text (e.g. password) when true is specified to hideEchoBack option. If you want to show nothing, specify ''. (But it might be not user friendly in some cases.)
Note: In some cases (e.g. when the input stream is redirected on Windows XP), '*' or '' might be used whether other one is specified.

For example:

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

limit

Limit the user's input.
The usage differ depending on the method.

For question* and prompt* methods

Type: string, number, RegExp, function or Array
Default: []

Accept only the input that matches value that is specified to this. If the user input others, display a string that is specified to limitMessage option, and wait for reinput.

• The string is compared with the input. It is affected by caseSensitive option.
• The number is compared with the input that is converted to number by parseFloat(). For example, it interprets ' 3.14 ', '003.1400', '314e-2' and '3.14PI' as 3.14. And it interprets '005', '5files', '5kb' and '5px' as 5.
• The RegExp tests the input.
• The function that returns a boolean to indicate whether it matches is called with the input.

One of above or an Array that includes multiple things (or Array includes Array) can be specified.

For example:

command = readlineSync.prompt({limit: ['add', 'remove', /^clear( all)?$/]});
// ** But `promptCL` method should be used instead of this. **

file = readlineSync.question('Text File: ', {limit: /\.txt$/i});
// ** But `questionPath` method should be used instead of this. **

ip = readlineSync.question('IP Address: ', {limit: function(input) {
  return require('net').isIP(input); // Valid IP Address
}});

availableActions = [];
if (!blockExists())  { availableActions.push('jump'); }
if (isLarge(place))  { availableActions.push('run'); }
if (isNew(shoes))    { availableActions.push('kick'); }
if (isNearby(enemy)) { availableActions.push('punch'); }
action = readlineSync.prompt({limit: availableActions});
// ** But `promptCL` method should be used instead of this. **

For keyIn* method

Type: string, number or Array
Default: []

Accept only the key that matches value that is specified to this, ignore others.
Specify the characters as the key. All strings or Array of those are decomposed into single characters. For example, 'abcde' or ['a', 'bc', ['d', 'e']] are the same as ['a', 'b', 'c', 'd', 'e'].
These strings are compared with the input. It is affected by caseSensitive option.

The placeholders like '$<a-e>' are replaced to an Array that is the character list like ['a', 'b', 'c', 'd', 'e'].

For example:

direction = readlineSync.keyIn('Left or Right? ', {limit: 'lr'}); // 'l' or 'r'

dice = readlineSync.keyIn('Roll the dice, What will the result be? ',
  {limit: '$<1-6>'}); // range of '1' to '6'

limitMessage

For question* and prompt* methods only
Type: string
Default: 'Input another, please.$<( [)limit(])>'

Display this to the user when the limit option is specified and the user input others.
The placeholders can be included.

For example:

file = readlineSync.question('Name of Text File: ', {
  limit: /\.txt$/i,
  limitMessage: 'Sorry, $<lastInput> is not text file.'
});

defaultInput

For question* and prompt* methods only
Type: string
Default: ''

If the user input empty text (i.e. pressed the Enter key only), return this.

For example:

lang = readlineSync.question('Which language? ', {defaultInput: 'javascript'});

trueValue, falseValue

Type: string, number, RegExp, function or Array
Default: []

If the input matches trueValue, return true. If the input matches falseValue, return false. In any other case, return the input.

• The string is compared with the input. It is affected by caseSensitive option.
• The number is compared with the input that is converted to number by parseFloat(). For example, it interprets ' 3.14 ', '003.1400', '314e-2' and '3.14PI' as 3.14. And it interprets '005', '5files', '5kb' and '5px' as 5. Note that in keyIn* method, the input is every time one character (i.e. the number that is specified must be an integer within the range of 0 to 9).
• The RegExp tests the input.
• The function that returns a boolean to indicate whether it matches is called with the input.

One of above or an Array that includes multiple things (or Array includes Array) can be specified.

For example:

answer = readlineSync.question('How do you like it? ', {
  trueValue: ['yes', 'yeah', 'yep'],
  falseValue: ['no', 'nah', 'nope']
});
if (answer === true) {
  console.log('Let\'s go!');
} else if (answer === false) {
  console.log('Oh... It\'s ok...');
} else {
  console.log('Sorry. What does "' + answer + '" you said mean?');
}

caseSensitive

Type: boolean
Default: false

By default, the string comparisons are case-insensitive (i.e. a equals A). If true is specified, it is case-sensitive, the cases are not ignored (i.e. a is different from A).
It affects: limit, trueValue, falseValue, some placeholders, and some Utility Methods.

keepWhitespace

For question* and prompt* methods only
Type: boolean
Default: false

By default, remove the leading and trailing white spaces from the input text. If true is specified, don't remove those.

encoding

Type: string
Default: 'utf8'

Set the encoding method of the input and output.

bufferSize

For question* and prompt* methods only
Type: number
Default: 1024

When readlineSync reads from a console directly (without external program), use a size bufferSize buffer.
Even if the input by user exceeds it, it's usually no problem, because the buffer is used repeatedly. But some platforms's (e.g. Windows) console might not accept input that exceeds it. And set an enough size.
Note that this might be limited by version of Node.js and environment running your script (Big buffer size is usually not required). (See also: issue, PR)

print

Type: function or undefined
Default: undefined

Call the specified function with every output. The function is given two arguments, display as an output text, and a value of encoding option.

For example:

• Pass the plain texts to the Logger (e.g. log4js), after clean the colored texts.

var readlineSync = require('readline-sync'),
  chalk = require('chalk'),
  log4js = require('log4js'),
  logger, user, pw, command;
 
log4js.configure({appenders: [{type: 'file', filename: 'fooApp.log'}]});
logger = log4js.getLogger('fooApp');
 
readlineSync.setDefaultOptions({
  print: function(display, encoding)
    { logger.info(chalk.stripColor(display)); }, // Remove ctrl-chars.
  prompt: chalk.red.bold('> ')
});
 
console.log(chalk.black.bold.bgYellow('    Your Account    '));
user = readlineSync.question(chalk.gray.underline(' USER NAME ') + ' : ');
pw = readlineSync.question(chalk.gray.underline(' PASSWORD  ') + ' : ',
  {hideEchoBack: true});
// Authorization ...
console.log(chalk.green('Welcome, ' + user + '!'));
command = readlineSync.prompt();

• Output a conversation to a file when an output stream is redirected to record those into a file like your-script >foo.log. That is, a conversation isn't outputted to foo.log without this code.

readlineSync.setDefaultOptions({
  print: function(display, encoding)
    { process.stdout.write(display, encoding); }
});
var name = readlineSync.question('May I have your name? ');
var loc = readlineSync.question('Hi ' + name + '! Where do you live? ');

• Let somebody hear our conversation in real time.
  It just uses a fifo with above sample code that was named conv.js.

Another terminal:

mkfifo /tmp/fifo
cat /tmp/fifo

My terminal:

node conv.js >/tmp/fifo

May I have your name? Oz
Hi Oz! Where do you live? Emerald City

And then, another terminal shows this synchronously:

May I have your name? Oz
Hi Oz! Where do you live? Emerald City

history

For question* and prompt* methods only
Type: boolean
Default: true

readlineSync supports a history expansion feature that is similar to that of the shell. If false is specified, disable this feature.
It keeps a previous input only. That is, only !!, !-1, !!:p and !-1:p like bash or zsh etc. are supported.

• !! or !-1: Return a previous input.
• !!:p or !-1:p: Display a previous input but do not return it, and wait for reinput.

For example:

while (true) {
  input = readlineSync.prompt();
  console.log('-- You said "' + input + '"');
}

> hello
-- You said "hello"
> !!
hello
-- You said "hello"
> !!:p
hello
> bye
-- You said "bye"

cd

For question* and prompt* methods only
Type: boolean
Default: false

readlineSync supports the changing the current working directory feature that is similar to the cd and pwd commands in the shell. If true is specified, enable this feature.
This helps the user when you let the user input the multiple local files or directories.
It supports cd and pwd commands.

• cd <path>: Change the current working directory to <path>. The <path> can include ~ as the home directory.
• pwd: Display the current working directory.

When these were input, do not return, and wait for reinput.

For example:

while (true) {
  file = readlineSync.questionPath('File: ');
  console.log('-- Specified file is ' + file);
}

File: cd foo-dir/bar-dir
File: pwd
/path/to/foo-dir/bar-dir
File: file-a.js
-- Specified file is /path/to/foo-dir/bar-dir/file-a.js
File: file-b.png
-- Specified file is /path/to/foo-dir/bar-dir/file-b.png
File: file-c.html
-- Specified file is /path/to/foo-dir/bar-dir/file-c.html

Utility Methods

questionEMail, questionNewPassword, questionInt, questionFloat, questionPath, promptCL, promptLoop, promptCLLoop, promptSimShell, keyInYN, keyInYNStrict, keyInPause, keyInSelect

These are convenient methods that are extended Basic Methods to be used easily.

questionEMail

email = readlineSync.questionEMail([query[, options]])

Display a query to the user if it's specified, and then accept only a valid e-mail address, and then return it after the Enter key was pressed.

The query is handled the same as that of the question method.
The default value of query is 'Input e-mail address: '.

Note: The valid e-mail address requirement is a willful violation of RFC5322, this is defined in HTML5. This works enough to prevent the user mistaking. If you want to change it, specify limit option.

For example:

email = readlineSync.questionEMail();
console.log('-- E-mail is ' + email);

Input e-mail address: abc
Input valid e-mail address, please.
Input e-mail address: mail@example.com
-- E-mail is mail@example.com

Options

The following options have independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

questionNewPassword

password = readlineSync.questionNewPassword([query[, options]])

Display a query to the user if it's specified, and then accept only a valid password, and then request same one again, and then return it after the Enter key was pressed.
It's the password, or something that is the secret text like the password.
You can specify the valid password requirement to the options.

The query is handled the same as that of the question method.
The default value of query is 'Input new password: '.

Note: Only the form of password is checked. Check it more if you want. For example, zxcvbn is password strength estimation library.

For example:

password = readlineSync.questionNewPassword();
console.log('-- Password is ' + password);

Input new password: ************
It can include: 0...9, A...Z, a...z, !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~
And the length must be: 12...24
Input new password: *************
Reinput a same one to confirm it: *************
It differs from first one. Hit only the Enter key if you want to retry from first one.
Reinput a same one to confirm it: *************
-- Password is _my_password_

Options

The following options have independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

And the following additional options are available.

charlist

Type: string
Default: '$<!-~>'

A string as the characters that can be included in the password. For example, if 'abc123' is specified, the passwords that include any character other than these 6 characters are refused.
The placeholders like '$<a-e>' are replaced to the characters like 'abcde'.

For example, let the user input a password that is created with alphabet and some symbols:

password = readlineSync.questionNewPassword('PASSWORD: ', {charlist: '$<a-z>#$@%'});

min, max

Type: number
Default: min: 12, max: 24

min: A number as a minimum length of the password.
max: A number as a maximum length of the password.

confirmMessage

Type: string or others
Default: 'Reinput a same one to confirm it: '

A message that lets the user input the same password again.
It can include the placeholders.
If this is not string, it is converted to string (i.e. toString method is called).

unmatchMessage

Type: string or others
Default: 'It differs from first one. Hit only the Enter key if you want to retry from first one.'

A warning message that is displayed when the second input did not match first one.
This is converted the same as the confirmMessage option.

Additional Placeholders

The following additional placeholder parameters are available.

charlist

A current value of charlist option that is converted to human readable if possible. (e.g. 'A...Z')

length

A current value of min and max option that is converted to human readable. (e.g. '12...24')

questionInt

numInt = readlineSync.questionInt([query[, options]])

Display a query to the user if it's specified, and then accept only an input that can be interpreted as an integer, and then return the number (not string) after the Enter key was pressed.
This parses the input as much as possible by parseInt(). For example, it interprets ' 5 ', '5.6', '005', '5files', '5kb' and '5px' as 5.

The query is handled the same as that of the question method.

Options

The following option has independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

questionFloat

numFloat = readlineSync.questionFloat([query[, options]])

Display a query to the user if it's specified, and then accept only an input that can be interpreted as a floating-point number, and then return the number (not string) after the Enter key was pressed.
This parses the input as much as possible by parseFloat(). For example, it interprets ' 3.14 ', '003.1400', '314e-2' and '3.14PI' as 3.14.

The query is handled the same as that of the question method.

Options

The following option has independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

questionPath

path = readlineSync.questionPath([query[, options]])

Display a query to the user if it's specified, and then accept only a valid local file or directory path, and then return an absolute path after the Enter key was pressed.
The ~ that is input by the user is replaced to the home directory.
You can specify the valid local file or directory path requirement to the options. And you can make it create a new file or directory when it doesn't exist.

It is recommended to use this method with the cd option. (Default: true)

The query is handled the same as that of the question method.
The default value of query is 'Input path (you can "cd" and "pwd"): '.

For example:

sourceFile = readlineSync.questionPath('Read from: ', {
  isFile: true
});
console.log('-- sourceFile: ' + sourceFile);
 
saveDir = readlineSync.questionPath('Save to: ', {
  isDirectory: true,
  exists: null,
  create: true
});
console.log('-- saveDir: ' + saveDir);

Read from: ~/fileA
No such file or directory: /home/user/fileA
Input valid path, please.
Read from: pwd
/path/to/work
Read from: cd ~/project-1
Read from: fileA
-- sourceFile: /home/user/project-1/fileA
Save to: ~/deploy/data
-- saveDir: /home/user/deploy/data

Options

The following options have independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

And the following additional options are available.

Note: It does not check the coherency about a combination of the options as the path requirement. For example, the {exists: false, isFile: true} never check that it is a file because it is limited to the path that does not exist.

exists

Type: boolean or others
Default: true

If true is specified, accept only a file or directory path that exists. If false is specified, accept only a file or directory path that does not exist.
In any other case, the existence is not checked.

min, max

Type: number or others
Default: undefined

min: A number as a minimum size of the file that is accepted.
max: A number as a maximum size of the file that is accepted.
If it is not specified or 0 is specified, the size is not checked. (A size of directory is 0.)

isFile, isDirectory

Type: boolean
Default: false

isFile: If true is specified, accept only a file path.
isDirectory: If true is specified, accept only a directory path.

validate

Type: function or undefined
Default: undefined

If a function that returns true or an error message is specified, call it with a path that was input, and accept the input when the function returned true.
If the function returned a string as an error message, that message is got by the error additional placeholder parameter.
A path that was input is parsed before it is passed to the function. ~ is replaced to a home directory, and a path is converted to an absolute path.
This is also a return value from this method.

For example, accept only PNG file or tell it to the user:

imageFile = readlineSync.questionPath('Image File: ', {
  validate: function(path) { return /\.png$/i.test(path) || 'It is not PNG'; }
});

create

Type: boolean
Default: false

If true is specified, create a file or directory as a path that was input when it doesn't exist. If true is specified to the isDirectory option, create a directory, otherwise a file.
It does not affect the existence check. Therefore, you can get a new file or directory path anytime by specifying: {exists: false, create: true}

Additional Placeholders

The following additional placeholder parameters are available.

error

An error message when the input was not accepted.
This value is set by readlineSync, or the function that was specified to validate option.

min, max

A current value of min and max option.

promptCL

argsArray = readlineSync.promptCL([commandHandler[, options]])

Display a prompt-sign (see prompt option) to the user, and then consider the input as a command-line and parse it, and then return a result after the Enter key was pressed.
A return value is an Array that includes the tokens that were parsed. It parses the input from the user as the command-line, and it interprets whitespaces, quotes, etc., and it splits it to tokens properly. Usually, a first element of the Array is command-name, and remaining elements are arguments.

For example:

argsArray = readlineSync.promptCL();
console.log(argsArray.join('\n'));

> command arg "arg" " a r g " "" 'a"r"g' "a""rg" "arg
command
arg
arg
 a r g 
 
a"r"g
arg
arg

commandHandler

By using the commandHandler argument, this method will come into its own. Specifying the Object to this argument has the more merit. And it has the more merit for promptCLLoop method.

If a function is specified to commandHandler argument, it is just called with a parsed Array as an argument list of the function. And this is an original input string, in the function.

For example, the following 2 codes work same except that this is enabled in the second one:

argsArray = readlineSync.promptCL();
if (argsArray[0] === 'add') {
  console.log(argsArray[1] + ' is added.');
} else if (argsArray[0] === 'copy') {
  console.log(argsArray[1] + ' is copied to ' + argsArray[2] + '.');
}

readlineSync.promptCL(function(command, arg1, arg2) {
  console.log('You want to: ' + this); // All of command-line.
  if (command === 'add') {
    console.log(arg1 + ' is added.');
  } else if (command === 'copy') {
    console.log(arg1 + ' is copied to ' + arg2 + '.');
  }
});

If an Object that has properties named as the command-name is specified, the command-name is interpreted, and a function as the value of matched property is called. A function is chosen properly by handling case of the command-name in accordance with the caseSensitive option.
The function is called with a parsed Array that excludes a command-name (i.e. first element is removed from the Array) as an argument list of the function.
That is, a structure of the commandHandler Object looks like:

{
  commandA: function(arg) { ... },        // commandA requires one argument.
  commandB: function(arg1, arg2) { ... }, // readlineSync doesn't care those.
  commandC: function() { ... }            // Of course, it can also ignore all.
}

readlineSync just receives the arguments from the user and passes those to these functions without checking. The functions may have to check whether the required argument was input by the user, and more validate those.

For example, the following code works same to the above code:

readlineSync.promptCL({
  add: function(element) { // It's called by also "ADD", "Add", "aDd", etc..
    console.log(element + ' is added.');
  },
  copy: function(from, to) {
    console.log(from + ' is copied to ' + to + '.');
  }
});

If the matched property is not found in the Object, a _ property is chosen, and the function as the value of this property is called with a parsed Array as an argument list of the function. Note that this includes a command-name. That is, the function looks like function(command, arg1, arg2, ...) { ... }.
And if the Object doesn't have a _ property, any command that the matched property is not found in the Object is refused.

For example:

readlineSync.promptCL({
  copy: function(from, to) { // command-name is not included.
    console.log(from + ' is copied to ' + to + '.');
  },
  _: function(command) { // command-name is included.
    console.log('Sorry, ' + command + ' is not available.');
  }
});

Options

The following options have independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

promptLoop

readlineSync.promptLoop(inputHandler[, options])

Display a prompt-sign (see prompt option) to the user, and then call inputHandler function with the input from the user after it has been typed and the Enter key was pressed. Do these repeatedly until inputHandler function returns true.

For example, the following 2 codes work same:

while (true) {
  input = readlineSync.prompt();
  console.log('-- You said "' + input + '"');
  if (input === 'bye') {
    break;
  }
}
console.log('It\'s exited from loop.');

readlineSync.promptLoop(function(input) {
  console.log('-- You said "' + input + '"');
  return input === 'bye';
});
console.log('It\'s exited from loop.');

> hello
-- You said "hello"
> good morning
-- You said "good morning"
> bye
-- You said "bye"
It's exited from loop.

Options

The following options have independent default value that is not affected by Default Options.

The other options work as shown in the Basic Options section.

promptCLLoop

readlineSync.promptCLLoop([commandHandler[, options]])

Execute promptCL method repeatedly until chosen commandHandler returns true.
The commandHandler may be a function that is called like:

exit = allCommands(command, arg1, arg2, ...);

or an Object that has the functions that are called like:

exit = foundCommand(arg1, arg2, ...);

See promptCL method for details.
This method looks like a combination of promptCL method and promptLoop method.

For example:

readlineSync.promptCLLoop({
  add: function(element) {
    console.log(element + ' is added.');
  },
  copy: function(from, to) {
    console.log(from + ' is copied to ' + to + '.');
  },
  bye: function() { return true; }
});
console.log('It\'s exited from loop.');

> add "New Hard Disk"
New Hard Disk is added.
> move filesOnOld "New Hard Disk"
Requested command is not available.
> copy filesOnOld "New Hard Disk"
filesOnOld is copied to New Hard Disk.
> bye
It's exited from loop.

Options

The following options have independent default value that is not affected by Default Options.

The following options work as shown in the Basic Options section.

promptSimShell

input = readlineSync.promptSimShell([options])

Display a prompt-sign that is similar to that of the user's shell to the user, and then return the input from the user after it has been typed and the Enter key was pressed.
This method displays a prompt-sign like:

On Windows:

C:\Users\User\Path\To\Directory>

On others:

user@host:~/path/to/directory$ 

Options

The following options have independent default value that is not affected by Default Options.

The other options other than prompt option work as shown in the Basic Options section.

keyInYN