Standard input/output management module for NodeJS
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lib _meta_ argument support added, allowing positional arguments constraints Dec 30, 2014
tests New test added Aug 19, 2014
.gitignore Do not reserve -h key and let users call printHelp() manually Sep 25, 2014
.jshintrc GetOpt module rewritten. Jasmine tests added Jul 26, 2014
.travis.yml Do not test with node 0.8 in Travis CI Aug 15, 2014 _meta_ argument support added, allowing positional arguments constraints Dec 30, 2014
LICENSE Update Jan 24, 2017
main.js Basic progress bars support added Sep 14, 2014
package.json _meta_ argument support added, allowing positional arguments constraints Dec 30, 2014

Module for standard input/output management with nodejs.

Build Status


Package Quality

1. Installation

To install the most recent release from npm, run:

npm install stdio

2. Usage

You can do many things with this module:

  • Parse UNIX-like command line options
  • Read standard input, at once or line by line.
  • Make command-line questions

2.1. Parse Unix-like command line options

var stdio = require('stdio');
var ops = stdio.getopt({
    'check': {key: 'c', args: 2, description: 'What this option means'},
    'map': {key: 'm', description: 'Another description', mandatory: true},
    'kaka': {key: 'k', args: 2, mandatory: true},
    'ooo': {key: 'o'}

If you run the previous example with the command

node pruebas.js -c 23 45 88 --map -k 23 44 cosa

Program output will be:

{ check: [ '23', '45' ],
  args: [ '88', 'cosa' ],
  map: true,
  kaka: [ '23', '44' ] }

So you can check options:

    // Your action
    // Your action, using ops.kaka[0] or ops.kaka[1] or...

As you can see, every option in ops object can have one of the following 3 types of values:

  • The boolean value true if it has been specified without an args attribute.
  • A single string if it has been specified with args: 1.
  • A string array, if it has been specified with args > 1.

Options can have the multiple flag, in which case they can appear multiple times (with one argument each time). The value of that option will be an array with all provided arguments:

var ops = stdio.getopt({
    'check': {key: 'c', description: 'What this option means', multiple: true}
node program.js -c 1 -c 2 -c 3
{ check: ['1', '2', '3'] }

When specifying an option, "args" can be the string "*" instead of a number, in which case all the following arguments when calling the program will be associated to that option (until the next one):

var ops = stdio.getopt({
    'check': {args: '*'},
	'meta': {key: 'm'}
node program.js --check 1 2 3 4 5 6 -m 44 2
{ check: ['1', '2', '3', '4', '5', '6'], meta: true, args: ['44', '2'] }

Default values can be specified using "default" attribute when specifying options. Of course, default value length has to match the specified args count (if it is not '*'):

var ops = stdio.getopt({
	something: {args: 2, default: ['a', 'b']}

Mandatory positional arguments

If your program has to receive some mandatory positional arguments (extra arguments without an option flag), you can specify it when calling getopt():

var ops = stdio.getopt({
	_meta_: {args: 2}
var ops = stdio.getopt({
	_meta_: {minArgs: 1}
var ops = stdio.getopt({
	_meta_: {maxArgs: 5}

Print usage

This module generates a descriptive usage message automatically. You'll see it when your program is called with --help option, which is automatically supported. The following code:

var stdio = require('stdio');

var ops = exports.getopt({
	una: {description: 'Sets something to some value', args: 2, mandatory: true},
	otra_muy_larga: {description: 'A boolean flag', key: 'o', mandatory: true},
	una_sin_desc: {description: 'Another boolean flag'},
	ultima: {description: 'A description', key: 'u', args: 1}

will produce the following output (if it is called with --help flag):

USAGE: node main.js [OPTION1] [OPTION2]... arg1 arg2...
  --una <ARG1> <ARG2>  	Sets something to some value (mandatory)
  -o, --otra_muy_larga 	A boolean flag (mandatory)
  --una_sin_desc       	Another boolean flag
  -u, --ultima <ARG1>  	A description

If a non-expected option is given or a mandatory option isn't, then an error will be shown, suggesting to use --help option to know how to use your program and finishing it automatically. In case the unknown option is similar to a known one, then a suggestion to use it will be shown.

Missing "una" argument.
Try "--help" for more information.

You can print the help message manually if you want, executing ops.printHelp().

2.2. Read standard input at once

The following code will read the whole standard input at once and put it into text variable.

var stdio = require('stdio');{

Obviously it is recommended only for small input streams, for instance a small file:

node myprogram.js < input-file.txt

2.3. Read standard input line by line

The following code will execute dynamically a function over every line, when it is read from the standard input:

var stdio = require('stdio');
stdio.readByLines(function lineHandler(line, index) {
    // You can do whatever you want with every line
    console.log('Line %d:', index, line);
}, function (err) {

The previous code will apply lineHandler() to every line while they are read, without waiting the whole input to end or buffering it, so it is very useful for large text streams. For instance a continuous log:

tail -f /var/log/system.log | node myprogram.js

2.4. Show prompt questions and wait user's answer

The following code will ask the user for some info and then print it.

stdio.question('What is your name?', function (err, name) {
    stdio.question('How old are you?', function (err, age) {
        stdio.question('Are you male or female?', ['male', 'female'], function (err, sex) {
            console.log('Your name is "%s". You are a "%s" "%s" years old.', name, sex, age);

By default stdio.question() offers some retries when allowed answers are restricted (see the male/female question above). If no possible answers are specified, then the user can answer whatever he wants to the question.

2.5. Show a progress bar

The following code will create a progress bar of 100 pieces and increments of 10. These values do not affect how the progress bar is shown, so a progress bar with 100 steps will be equals to a progress bar with 4 steps. Every call to tick() increments the bar value. Remaining time is estimated dynamically:

var stdio = require('stdio');

var pbar = stdio.progressBar(100, 10);
var i = setInterval(function () {
}, 1000);
pbar.onFinish(function () {

The progress bar is updated in real-time:

00:00:03 25% [###############························] ETA 00:00:09

Instead of calling tick() it is possible to force the progress bar value at any time:


3. Testing

To run tests, use the following command from module's root:

npm test