The yargs npm package is a command-line argument parser that helps in building interactive command line tools, by parsing arguments and generating an elegant user interface. It provides a simple and efficient way to handle command line arguments for Node.js applications.
Command Parsing
Yargs allows you to define commands and associated options. This feature is useful for CLI applications that perform different actions based on the command provided.
const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.command('get', 'make a get HTTP request', () => {}, (argv) => {
console.log(`Request made to URL: ${argv.url}`);
}).argv;Option Parsing
Yargs can parse options (also known as flags or switches) with additional configuration such as aliases, types, and descriptions.
const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.option('verbose', {
alias: 'v',
type: 'boolean',
description: 'Run with verbose logging'
}).argv;Default Values
Yargs allows setting default values for options, which will be used if no value is provided by the user.
const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.default('port', 8080).argv;Automatic Help and Version Information
Yargs can automatically generate help and version information for the CLI tool, making it easier for users to understand how to use the application.
const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.help().version().argv;Custom Validation
Yargs provides a way to define custom validation rules for the provided arguments, ensuring that the input meets certain criteria before the application proceeds.
const yargs = require('yargs/yargs')(process.argv.slice(2));
yargs.option('port', {
describe: 'The port to bind on',
demandOption: true,
number: true
}).check((argv, options) => {
if (argv.port < 1024) {
throw new Error('Port must be at least 1024');
}
return true;
}).argv;Commander is another popular npm package for parsing command-line options. It provides a high-level API for defining commands and options, similar to yargs. Commander is known for its simplicity and declarative approach to command-line arguments.
Minimist is a minimalistic command-line argument parser. It is more lightweight than yargs and focuses on parsing a list of arguments into an object, without the additional features like command handling, help text generation, or validation.
Meow is a CLI helper for creating Node.js command-line apps. It provides a simpler and more opinionated API compared to yargs, with built-in help text, version output, and flag aliasing. Meow is suitable for smaller projects that require less customization.
Caporal is a full-featured framework for building command-line applications. It offers a rich set of features including argument parsing, validation, autocomplete, and more. Caporal is more framework-like compared to yargs, which might be more suitable for complex CLI tools.
Yargs be a node.js library fer hearties tryin' ter parse optstrings.
With yargs, ye be havin' a map that leads straight to yer treasure! Treasure of course, being a simple option hash.
Yargs is the official successor to optimist. Please feel free to submit issues and pull requests. If you'd like to contribute and don't know where to start, have a look at the issue list :)
plunder.js:
#!/usr/bin/env node
var argv = require('yargs').argv;
if (argv.ships > 3 && argv.distance < 53.5) {
console.log('Plunder more riffiwobbles!');
}
else {
console.log('Retreat from the xupptumblers!');
}
$ ./plunder.js --ships=4 --distance=22
Plunder more riffiwobbles!
$ ./plunder.js --ships 12 --distance 98.7
Retreat from the xupptumblers!
short.js:
#!/usr/bin/env node
var argv = require('yargs').argv;
console.log('(%d,%d)', argv.x, argv.y);
$ ./short.js -x 10 -y 21
(10,21)
bool.js:
#!/usr/bin/env node
var util = require('util');
var argv = require('yargs').argv;
if (argv.s) {
util.print(argv.fr ? 'Le perroquet dit: ' : 'The parrot says: ');
}
console.log(
(argv.fr ? 'couac' : 'squawk') + (argv.p ? '!' : '')
);
$ ./bool.js -s
The parrot says: squawk
$ ./bool.js -sp
The parrot says: squawk!
$ ./bool.js -sp --fr
Le perroquet dit: couac!
argv._!nonopt.js:
#!/usr/bin/env node
var argv = require('yargs').argv;
console.log('(%d,%d)', argv.x, argv.y);
console.log(argv._);
$ ./nonopt.js -x 6.82 -y 3.35 rum
(6.82,3.35)
[ 'rum' ]
$ ./nonopt.js "me hearties" -x 0.54 yo -y 1.12 ho
(0.54,1.12)
[ 'me hearties', 'yo', 'ho' ]
count.js
#!/usr/bin/env node
var argv = require('yargs')
.count('verbose')
.alias('v', 'verbose')
.argv;
VERBOSE_LEVEL = argv.verbose;
function WARN() { VERBOSE_LEVEL >= 0 && console.log.apply(console, arguments); }
function INFO() { VERBOSE_LEVEL >= 1 && console.log.apply(console, arguments); }
function DEBUG() { VERBOSE_LEVEL >= 2 && console.log.apply(console, arguments); }
WARN("Showing only important stuff");
INFO("Showing semi-mportant stuff too");
DEBUG("Extra chatty mode");
$ node count.js
Showing only important stuff
$ node count.js -v
Showing only important stuff
Showing semi-important stuff too
$ node count.js -vv
Showing only important stuff
Showing semi-important stuff too
Extra chatty mode
$ node count.js -v --verbose
Showing only important stuff
Showing semi-important stuff too
Extra chatty mode
area.js:
#!/usr/bin/env node
var argv = require('yargs')
.usage('Usage: $0 -w [num] -yh[num]')
.demand(['w','h'])
.argv;
console.log("The area is:", argv.w * argv.h);
$ ./area.js -w 55 -h 11
605
$ node ./area.js -w 4.91 -w 2.51
Usage: node ./area.js -w [num] -h [num]
Options:
-w [required]
-h [required]
Missing required arguments: h
demand_count.js:
#!/usr/bin/env node
var argv = require('yargs')
.demand(2)
.argv;
console.dir(argv)
$ ./demand_count.js a
Not enough arguments, expected 2, but only found 1
$ ./demand_count.js a b
{ _: [ 'a', 'b' ], '$0': 'node ./demand_count.js' }
$ ./demand_count.js a b c
{ _: [ 'a', 'b', 'c' ], '$0': 'node ./demand_count.js' }
default_singles.js:
#!/usr/bin/env node
var argv = require('yargs')
.default('x', 10)
.default('y', 10)
.argv
;
console.log(argv.x + argv.y);
$ ./default_singles.js -x 5
15
default_hash.js:
#!/usr/bin/env node
var argv = require('yargs')
.default({ x : 10, y : 10 })
.argv
;
console.log(argv.x + argv.y);
$ ./default_hash.js -y 7
17
boolean_single.js
#!/usr/bin/env node
var argv = require('yargs')
.boolean('v')
.argv
;
console.dir(argv.v);
console.dir(argv._);
$ ./boolean_single.js -v "me hearties" yo ho
true
[ 'me hearties', 'yo', 'ho' ]
boolean_double.js
#!/usr/bin/env node
var argv = require('yargs')
.boolean(['x','y','z'])
.argv
;
console.dir([ argv.x, argv.y, argv.z ]);
console.dir(argv._);
$ ./boolean_double.js -x -z one two three
[ true, false, true ]
[ 'one', 'two', 'three' ]
Ye can describe parameters fer help messages and set aliases. Yargs figures out how ter format a handy help string automatically.
line_count.js
#!/usr/bin/env node
var argv = require('yargs')
.usage('Usage: $0 <command> [options]')
.command('count', 'Count the lines in a file')
.demand(1)
.example('$0 count -f foo.js', 'count the lines in the given file')
.demand('f')
.alias('f', 'file')
.nargs('f', 1)
.describe('f', 'Load a file')
.help('h')
.alias('h', 'help')
.epilog('copyright 2015')
.argv;
var fs = require('fs');
var s = fs.createReadStream(argv.file);
var lines = 0;
s.on('data', function (buf) {
lines += buf.toString().match(/\n/g).length;
});
s.on('end', function () {
console.log(lines);
});
$ node line_count.js count
Usage: node test.js <command> [options]
Commands:
count Count the lines in a file
Options:
-f, --file Load a file [required]
-h, --help Show help
Examples:
node test.js count -f foo.js count the lines in the given file
copyright 2015
Missing required arguments: f
$ node line_count.js count --file line_count.js
20
$ node line_count.js count -f line_count.js
20
By itself,
require('yargs').argv
will use process.argv array to construct the argv object.
You can pass in the process.argv yourself:
require('yargs')([ '-x', '1', '-y', '2' ]).argv
or use .parse() to do the same thing:
require('yargs').parse([ '-x', '1', '-y', '2' ])
The rest of these methods below come in just before the terminating .argv.
Set key names as equivalent such that updates to a key will propagate to aliases and vice-versa.
Optionally .alias() can take an object that maps keys to aliases.
Each key of this object should be the canonical version of the option, and each
value should be a string or an array of strings.
Set argv[key] to value if no option was specified on process.argv.
Optionally .default() can take an object that maps keys to default values.
But wait, there's more! the default value can be a function which returns
a value. The name of the function will be used in the usage string:
var argv = require('yargs')
.default('random', function randomValue() {
return Math.random() * 256;
}).argv;
Optionally, description can also be provided and will take precedence over
displaying the value in the usage instructions:
.default('timeout', 60000, '(one-minute)');
If key is a string, show the usage information and exit if key wasn't
specified in process.argv.
If key is a number, demand at least as many non-option arguments, which show
up in argv._.
If key is an Array, demand each element.
If a msg string is given, it will be printed when the argument is missing,
instead of the standard error message. This is especially helpful for the non-option arguments in argv._.
If a boolean value is given, it controls whether the option is demanded;
this is useful when using .options() to specify command line parameters.
Specifies either a single option key (string), or an array of options that must be followed by option values. If any option value is missing, show the usage information and exit.
The default behaviour is to set the value of any key not followed by an
option value to true.
Given the key x is set, it is required that the key y is set.
implies can also accept an object specifying multiple implications.
Describe a key for the generated usage information.
Optionally .describe() can take an object that maps keys to descriptions.
Instead of chaining together .alias().demand().default().describe().string(), you can specify
keys in opt for each of the chainable methods.
For example:
var argv = require('yargs')
.option('f', {
alias : 'file',
demand: true,
default: '/etc/passwd',
describe: 'x marks the spot',
type: 'string'
})
.argv
;
is the same as
var argv = require('yargs')
.alias('f', 'file')
.default('f', '/etc/passwd')
.argv
;
Optionally .options() can take an object that maps keys to opt parameters.
var argv = require('yargs')
.options({
'f': {
alias: 'file',
demand: true,
default: '/etc/passwd',
describe: 'x marks the spot',
type: 'string'
}
})
.argv
;
Set a usage message to show which commands to use. Inside message, the string
$0 will get interpolated to the current script name or node command for the
present script similar to how $0 works in bash or perl.
opts is optional and acts like calling .options(opts).
Document the commands exposed by your application.
use desc to provide a description for each command your application accepts (the
values stored in argv._).
Optionally, you can provide a handler fn which will be executed when
a given command is provided. The handler will be executed with an instance
of yargs, which can be used to compose nested commands.
Here's an example of top-level and nested commands in action:
var argv = require('yargs')
.usage('npm <command>')
.command('install', 'tis a mighty fine package to install')
.command('publish', 'shiver me timbers, should you be sharing all that', function (yargs) {
argv = yargs.option('f', {
alias: 'force',
description: 'yar, it usually be a bad idea'
})
.help('help')
.argv
})
.help('help')
.argv;
Give some example invocations of your program. Inside cmd, the string
$0 will get interpolated to the current script name or node command for the
present script similar to how $0 works in bash or perl.
Examples will be printed out as part of the help message.
A message to print at the end of the usage instructions, e.g.,
var argv = require('yargs')
.epilogue('for more information, find our manual at http://example.com');
Check that certain conditions are met in the provided arguments.
fn is called with two arguments, the parsed argv hash and an array of options and their aliases.
If fn throws or returns a non-truthy value, show the thrown error, usage information, and
exit.
Method to execute when a failure occurs, rather then printing the failure message.
fn is called with the failure message that would have been printed.
Interpret key as a boolean. If a non-flag option follows key in
process.argv, that string won't get set as the value of key.
key will default to false, unless an default(key, undefined) is
explicitly set.
If key is an Array, interpret all the elements as booleans.
Tell the parser logic not to interpret key as a number or boolean.
This can be useful if you need to preserve leading zeros in an input.
If key is an Array, interpret all the elements as strings.
.string('_') will result in non-hyphenated arguments being interpreted as strings,
regardless of whether they resemble numbers.
Tell the parser to interpret key as an array. If .array('foo') is set,
--foo foo bar will be parsed as ['foo', 'bar'] rather than as 'bar'.
The number of arguments that should be consumed after a key. This can be a useful hint to prevent parsing ambiguity:
var argv = require('yargs')
.nargs('token', 1)
.parse(['--token', '-my-token']);
parses as:
{ _: [], token: '-my-token', '$0': 'node test' }
Optionally .nargs() can take an object of key/narg pairs.
Tells the parser that if the option specified by key is passed in, it
should be interpreted as a path to a JSON config file. The file is loaded
and parsed, and its properties are set as arguments.
Format usage output to wrap at columns many columns.
By default wrap will be set to Math.min(80, windowWidth). Use .wrap(null) to
specify no column limit.
yargs.wrap(yargs.terminalWidth()) can be used to maximize the width
of yargs' usage instructions.
Any command-line argument given that is not demanded, or does not have a corresponding description, will be reported as an error.
Add an option (e.g., --help) that displays the usage string and exits the
process. If present, the description parameter customises the description of
the help option in the usage string.
If invoked without parameters, .help returns the generated usage string.
Example:
var yargs = require("yargs")
.usage("$0 -operand1 number -operand2 number -operation [add|subtract]");
console.log(yargs.help());
Later on, argv can be retrived with yargs.argv
Add an option (e.g., --version) that displays the version number (given by the
version parameter) and exits the process. If present, the description
parameter customizes the description of the version option in the usage string.
You can provide a function for version, rather than a string.
This is useful if you want to use the version from your package.json:
var argv = require('yargs')
.version(function() {
return require('../package').version;
})
.argv;
By default, yargs outputs a usage string if any error is detected. Use the
.showHelpOnFail method to customize this behaviour. if enable is false,
the usage string is not output. If the message parameter is present, this
message is output after the error message.
line_count.js
#!/usr/bin/env node
var argv = require('yargs')
.usage('Count the lines in a file.\nUsage: $0')
.demand('f')
.alias('f', 'file')
.describe('f', 'Load a file')
.showHelpOnFail(false, "Specify --help for available options")
.argv;
// etc.
$ node line_count.js --file
Missing argument value: f
Specify --help for available options
Print the usage data using the console function consoleLevel for printing.
Example:
var yargs = require("yargs")
.usage("$0 -operand1 number -operand2 number -operation [add|subtract]");
yargs.showHelp();
Or, to print the usage data to stdout instead, you can specify the use of console.log:
yargs.showHelp("log");
Later on, argv can be retrived with yargs.argv
Enable bash-completion shortcuts for commands and options.
cmd: when present in argv._, will result in the .bashrc completion script
being outputted. To enable bash completions, concat the generated script to your
.bashrc, or .bash_profile.
description: provide a description in your usage instructions for the command
that generates bash completion scripts.
fn, rather than relying on yargs' default completion functionlity, which
shiver me timbers is pretty awesome, you can provide your own completion
method.
var argv = require('yargs')
.completion('completion', function(current, argv) {
// 'current' is the current command being completed.
// 'argv' is the parsed arguments so far.
// simply return an array of completions.
return [
'foo',
'bar'
];
})
.argv;
But wait, there's more! you can provide asynchronous completions.
var argv = require('yargs')
.completion('completion', function(current, argv, done) {
setTimeout(function() {
done([
'apple',
'banana'
]);
}, 500);
})
.argv;
Generate a bash completion script. Users of your application can install this
script in their .bashrc, and yargs will provide completion shortcuts for
commands and options.
By default, yargs exits the process when the user passes a help flag, uses the .version functionality or when validation fails. Calling .exitProcess(false) disables this behavior, enabling further actions after yargs have been validated.
Parse args instead of process.argv. Returns the argv object.
Reset the argument object built up so far. This is useful for creating nested command line interfaces.
var yargs = require('./yargs')
.usage('$0 command')
.command('hello', 'hello command')
.command('world', 'world command')
.demand(1, 'must provide a valid command'),
argv = yargs.argv,
command = argv._[0];
if (command === 'hello') {
yargs.reset()
.usage('$0 hello')
.help('h')
.example('$0 hello', 'print the hello message!')
.argv
console.log('hello!');
} else if (command === 'world'){
yargs.reset()
.usage('$0 world')
.help('h')
.example('$0 world', 'print the world message!')
.argv
console.log('world!');
} else {
yargs.showHelp();
}
Get the arguments as a plain old object.
Arguments without a corresponding flag show up in the argv._ array.
The script name or node command is available at argv.$0 similarly to how $0
works in bash or perl.
Use -- to stop parsing flags and stuff the remainder into argv._.
$ node examples/reflect.js -a 1 -b 2 -- -c 3 -d 4
{ _: [ '-c', '3', '-d', '4' ],
'$0': 'node ./examples/reflect.js',
a: 1,
b: 2 }
If you want to explicity set a field to false instead of just leaving it
undefined or to override a default you can do --no-key.
$ node examples/reflect.js -a --no-b
{ _: [],
'$0': 'node ./examples/reflect.js',
a: true,
b: false }
Every argument that looks like a number (!isNaN(Number(arg))) is converted to
one. This way you can just net.createConnection(argv.port) and you can add
numbers out of argv with + without having that mean concatenation,
which is super frustrating.
If you specify a flag multiple times it will get turned into an array containing all the values in order.
$ node examples/reflect.js -x 5 -x 8 -x 0
{ _: [],
'$0': 'node ./examples/reflect.js',
x: [ 5, 8, 0 ] }
When you use dots (.s) in argument names, an implicit object path is assumed.
This lets you organize arguments into nested objects.
$ node examples/reflect.js --foo.bar.baz=33 --foo.quux=5
{ _: [],
'$0': 'node ./examples/reflect.js',
foo: { bar: { baz: 33 }, quux: 5 } }
Short numeric head -n5 style argument work too:
$ node reflect.js -n123 -m456
{ '3': true,
'6': true,
_: [],
'$0': 'node ./reflect.js',
n: 123,
m: 456 }
With npm, just do:
npm install yargs
or clone this project on github:
git clone http://github.com/bcoe/yargs.git
To run the tests with npm, just do:
npm test
This module is loosely inspired by Perl's Getopt::Casual.
FAQs
yargs the modern, pirate-themed, successor to optimist.
We found that yargs demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 2 open source maintainers collaborating on the project.
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