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 argv = require('yargs').argv;
if (argv.s) {
process.stdout.write(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-important 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] -h [num]')
.demandOption(['w','h'])
.argv;
console.log("The area is:", argv.w * argv.h);
$ ./area.js -w 55 -h 11
The area is: 605
$ node ./area.js -w 4.91 -w 2.51
Usage: 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')
.demandCommand(2)
.argv;
console.dir(argv);
$ ./demand_count.js a
Not enough non-option arguments: got 1, need at least 2
$ ./demand_count.js a b
{ _: [ 'a', 'b' ], '$0': 'demand_count.js' }
$ ./demand_count.js a b c
{ _: [ 'a', 'b', 'c' ], '$0': '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')
.example('$0 count -f foo.js', 'count the lines in the given file')
.alias('f', 'file')
.nargs('f', 1)
.describe('f', 'Load a file')
.demandOption(['f'])
.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: line_count.js <command> [options]
Commands:
count Count the lines in a file
Options:
-f, --file Load a file [required]
-h, --help Show help [boolean]
Examples:
line_count.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
26
$ node line_count.js count -f line_count.js
26
By itself,
require('yargs').argv
will use the 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.
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.
If yargs is executed in an environment that embeds node and there's no script name (e.g.
Electron or nw.js), it will ignore the first parameter since it
expects it to be the script name. In order to override this behavior, use .parse(process.argv.slice(1))
instead of .argv and the first parameter won't be ignored.
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 'foo'.
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 a default(key, undefined) is
explicitly set.
If key is an array, interpret all the elements as booleans.
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.
Limit valid values for key to a predefined set of choices, given as an array
or as an individual value.
var argv = require('yargs')
.alias('i', 'ingredient')
.describe('i', 'choose your sandwich ingredients')
.choices('i', ['peanut-butter', 'jelly', 'banana', 'pickles'])
.help('help')
.argv
If this method is called multiple times, all enumerated values will be merged together. Choices are generally strings or numbers, and value matching is case-sensitive.
Optionally .choices() can take an object that maps multiple keys to their
choices.
Choices can also be specified as choices in the object given to option().
var argv = require('yargs')
.option('size', {
alias: 's',
describe: 'choose a size',
choices: ['xs', 's', 'm', 'l', 'xl']
})
.argv
Provide a synchronous function to coerce or transform the value(s) given on the
command line for key.
The coercion function should accept one argument, representing the parsed value
from the command line, and should return a new value or throw an error. The
returned value will be used as the value for key (or one of its aliases) in
argv.
If the function throws, the error will be treated as a validation
failure, delegating to either a custom .fail() handler or printing
the error message in the console.
Coercion will be applied to a value after
all other modifications, such as .normalize().
Examples:
var argv = require('yargs')
.coerce('file', function (arg) {
return require('fs').readFileSync(arg, 'utf8')
})
.argv
Optionally .coerce() can take an object that maps several keys to their
respective coercion function.
var argv = require('yargs')
.coerce({
date: Date.parse,
json: JSON.parse
})
.argv
You can also map the same function to several keys at one time. Just pass an
array of keys as the first argument to .coerce():
var path = require('path')
var argv = require('yargs')
.coerce(['src', 'dest'], path.resolve)
.argv
If you are using dot-notion or arrays, .e.g., user.email and user.password,
coercion will be applied to the final object that has been parsed:
// --user.name Batman --user.password 123
// gives us: {name: 'batman', password: '[SECRET]'}
var argv = require('yargs')
.option('user')
.coerce('user', opt => {
opt.name = opt.name.toLowerCase()
opt.password = '[SECRET]'
return opt
})
.argv
Define the commands exposed by your application.
cmd should be a string representing the command or an array of strings
representing the command and its aliases. Read more about command aliases in the
subsection below.
Use desc to provide a description for each command your application accepts (the
values stored in argv._). Set desc to false to create a hidden command.
Hidden commands don't show up in the help output and aren't available for
completion.
Optionally, you can provide a builder object to give hints about the
options that your command accepts:
yargs
.command('get', 'make a get HTTP request', {
url: {
alias: 'u',
default: 'http://yargs.js.org/'
}
})
.help()
.argv
Note that commands will not automatically inherit configuration or options of their parent context. This means you'll have to re-apply configuration if necessary, and make options global manually using the global method.
Additionally, the help and version
options (if used) always apply globally, just like the
.wrap() configuration.
builder can also be a function. This function is executed
with a yargs instance, and can be used to provide advanced command specific help:
yargs
.command('get', 'make a get HTTP request', function (yargs) {
return yargs.option('url', {
alias: 'u',
default: 'http://yargs.js.org/'
})
})
.help()
.argv
You can also provide a handler function, which will be executed with the
parsed argv object:
yargs
.command(
'get',
'make a get HTTP request',
function (yargs) {
return yargs.option('u', {
alias: 'url',
describe: 'the URL to make an HTTP request to'
})
},
function (argv) {
console.log(argv.url)
}
)
.help()
.argv
Commands can accept optional and required positional arguments. Required
positional arguments take the form <foo>, and optional arguments
take the form [bar]. The parsed positional arguments will be populated in
argv:
yargs.command('get <source> [proxy]', 'make a get HTTP request')
.help()
.argv
Aliases can be provided for positional arguments using the | character.
As an example, suppose our application allows either a username or
an email as the first argument:
yargs.command('get <username|email> [password]', 'fetch a user by username or email.')
.help()
.argv
In this way, both argv.username and argv.email would be populated with the
same value when the command is executed.
The last positional argument can optionally accept an array of
values, by using the .. operator:
yargs.command('download <url> [files..]', 'download several files')
.help()
.argv
When a command is given on the command line, yargs will execute the following:
builder, if givenhandler function, if givenYou can define aliases for a command by putting the command and all of its aliases into an array.
Alternatively, a command module may specify an aliases property, which may be
a string or an array of strings. All aliases defined via the command property
and the aliases property will be concatenated together.
The first element in the array is considered the canonical command, which may define positional arguments, and the remaining elements in the array are considered aliases. Aliases inherit positional args from the canonical command, and thus any positional args defined in the aliases themselves are ignored.
If either the canonical command or any of its aliases are given on the command line, the command will be executed.
#!/usr/bin/env node
require('yargs')
.command(['start [app]', 'run', 'up'], 'Start up an app', {}, (argv) => {
console.log('starting up the', argv.app || 'default', 'app')
})
.command({
command: 'configure <key> [value]',
aliases: ['config', 'cfg'],
desc: 'Set a config variable',
builder: (yargs) => yargs.default('value', 'true'),
handler: (argv) => {
console.log(`setting ${argv.key} to ${argv.value}`)
}
})
.demandCommand(1)
.help()
.wrap(72)
.argv
$ ./svc.js help
Commands:
start [app] Start up an app [aliases: run, up]
configure <key> [value] Set a config variable [aliases: config, cfg]
Options:
--help Show help [boolean]
$ ./svc.js cfg concurrency 4
setting concurrency to 4
$ ./svc.js run web
starting up the web app
For complicated commands you can pull the logic into a module. A module simply needs to export:
exports.command: string (or array of strings) that executes this command when given on the command line, first string may contain positional argsexports.aliases: array of strings (or a single string) representing aliases of exports.command, positional args defined in an alias are ignoredexports.describe: string used as the description for the command in help text, use false for a hidden commandexports.builder: object declaring the options the command accepts, or a function accepting and returning a yargs instanceexports.handler: a function which will be passed the parsed argv.// my-module.js
exports.command = 'get <source> [proxy]'
exports.describe = 'make a get HTTP request'
exports.builder = {
banana: {
default: 'cool'
},
batman: {
default: 'sad'
}
}
exports.handler = function (argv) {
// do something with argv.
}
You then register the module like so:
yargs.command(require('my-module'))
.help()
.argv
Or if the module does not export command and describe (or if you just want to override them):
yargs.command('get <source> [proxy]', 'make a get HTTP request', require('my-module'))
.help()
.argv
Apply command modules from a directory relative to the module calling this method.
This allows you to organize multiple commands into their own modules under a
single directory and apply all of them at once instead of calling
.command(require('./dir/module')) multiple times.
By default, it ignores subdirectories. This is so you can use a directory structure to represent your command hierarchy, where each command applies its subcommands using this method in its builder function. See the example below.
Note that yargs assumes all modules in the given directory are command modules
and will error if non-command modules are encountered. In this scenario, you
can either move your module to a different directory or use the exclude or
visit option to manually filter it out. More on that below.
directory is a relative directory path as a string (required).
opts is an options object (optional). The following options are valid:
recurse: boolean, default false
Look for command modules in all subdirectories and apply them as a flattened (non-hierarchical) list.
extensions: array of strings, default ['js']
The types of files to look for when requiring command modules.
visit: function
A synchronous function called for each command module encountered. Accepts
commandObject, pathToFile, and filename as arguments. Returns
commandObject to include the command; any falsy value to exclude/skip it.
include: RegExp or function
Whitelist certain modules. See require-directory whitelisting for details.
exclude: RegExp or function
Blacklist certain modules. See require-directory blacklisting for details.
.commandDir()Desired CLI:
$ myapp --help
$ myapp init
$ myapp remote --help
$ myapp remote add base http://yargs.js.org
$ myapp remote prune base
$ myapp remote prune base fork whatever
Directory structure:
myapp/
├─ cli.js
└─ cmds/
├─ init.js
├─ remote.js
└─ remote_cmds/
├─ add.js
└─ prune.js
cli.js:
#!/usr/bin/env node
require('yargs')
.commandDir('cmds')
.demandCommand(1)
.help()
.argv
cmds/init.js:
exports.command = 'init [dir]'
exports.desc = 'Create an empty repo'
exports.builder = {
dir: {
default: '.'
}
}
exports.handler = function (argv) {
console.log('init called for dir', argv.dir)
}
cmds/remote.js:
exports.command = 'remote <command>'
exports.desc = 'Manage set of tracked repos'
exports.builder = function (yargs) {
return yargs.commandDir('remote_cmds')
}
exports.handler = function (argv) {}
cmds/remote_cmds/add.js:
exports.command = 'add <name> <url>'
exports.desc = 'Add remote named <name> for repo at url <url>'
exports.builder = {}
exports.handler = function (argv) {
console.log('adding remote %s at url %s', argv.name, argv.url)
}
cmds/remote_cmds/prune.js:
exports.command = 'prune <name> [names..]'
exports.desc = 'Delete tracked branches gone stale for remotes'
exports.builder = {}
exports.handler = function (argv) {
console.log('pruning remotes %s', [].concat(argv.name).concat(argv.names).join(', '))
}
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 functionality, which
shiver me timbers is pretty awesome, you can provide your own completion
method.
If invoked without parameters, .completion() will make completion the command to output
the completion script.
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;
You can also provide asynchronous completions.
var argv = require('yargs')
.completion('completion', function(current, argv, done) {
setTimeout(function() {
done([
'apple',
'banana'
]);
}, 500);
})
.argv;
But wait, there's more! You can return an asynchronous promise.
var argv = require('yargs')
.completion('completion', function(current, argv, done) {
return new Promise(function (resolve, reject) {
setTimeout(function () {
resolve(['apple', 'banana'])
}, 10)
})
})
.argv;
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. Because the file is
loaded using Node's require(), the filename MUST end in .json to be
interpreted correctly.
If invoked without parameters, .config() will make --config the option to pass the JSON config file.
An optional description can be provided to customize the config (key) option
in the usage string.
An optional parseFn can be used to provide a custom parser. The parsing
function must be synchronous, and should return an object containing
key value pairs or an error.
var argv = require('yargs')
.config('settings', function (configPath) {
return JSON.parse(fs.readFileSync(configPath, 'utf-8'))
})
.argv
You can also pass an explicit configuration object, it will be parsed
and its properties will be set as arguments.
var argv = require('yargs')
.config({foo: 1, bar: 2})
.argv
console.log(argv)
$ node test.js
{ _: [],
foo: 1,
bar: 2,
'$0': 'test.js' }
Given the key x is set, the key y must not be set.
Optionally .conflicts() can accept an object specifying multiple conflicting keys.
Interpret key as a boolean flag, but set its parsed value to the number of
flag occurrences rather than true or false. Default value is thus 0.
Note: The .defaults() alias is deprecated. It will be
removed in the next major version.
Set argv[key] to value if no option was specified in 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)')
demand() has been deprecated, please instead see demandOption() and
demandCommand().
If key is a string, show the usage information and exit if key wasn't
specified in process.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.
// demand an array of keys to be provided
require('yargs')
.option('run', {
alias: 'r',
describe: 'run your program'
})
.option('path', {
alias: 'p',
describe: 'provide a path to file'
})
.option('spec', {
alias: 's',
describe: 'program specifications'
})
.demandOption(['run', 'path'], 'Please provide both run and path arguments to work with this tool')
.help()
.argv
which will provide the following output:
Options:
--run, -r run your program [required]
--path, -p provide a path to file [required]
--spec, -s program specifications
--help Show help [boolean]
Missing required arguments: run, path
Please provide both run and path arguments to work with this tool
If a boolean value is given, it controls whether the option is demanded;
this is useful when using .options() to specify command line parameters.
// demand individual options within the option constructor
require('yargs')
.options({
'run': {
alias: 'r',
describe: 'run your program',
demand: true
},
'path': {
alias: 'p',
describe: 'provide a path to file',
demand: true
},
'spec': {
alias: 's',
describe: 'program specifications'
}
})
.help()
.argv
which will provide the following output:
Options:
--run, -r run your program [required]
--path, -p provide a path to file [required]
--spec, -s program specifications
--help Show help [boolean]
Missing required arguments: run, path
Demand in context of commands. You can demand a minimum and a maximum number a user can have within your program, as well as provide corresponding error messages if either of the demands is not met.
require('yargs')
.command({
command: 'configure <key> [value]',
aliases: ['config', 'cfg'],
desc: 'Set a config variable',
builder: (yargs) => yargs.default('value', 'true'),
handler: (argv) => {
console.log(`setting ${argv.key} to ${argv.value}`)
}
})
// provide a minimum demand and a minimum demand message
.demandCommand(1, 'You need at least one command before moving on')
.help()
.argv
which will provide the following output:
Commands:
configure <key> [value] Set a config variable [aliases: config, cfg]
Options:
--help Show help [boolean]
You need at least one command before moving on
Note: in minMsg and maxMsg, every occurrence of $0 will be replaced
with the observed value, and every instance of $1 will be replaced with the
expected value.
Describe a key for the generated usage information.
Optionally .describe() can take an object that maps keys to descriptions.
Should yargs attempt to detect the os' locale? Defaults to true.
Tell yargs to parse environment variables matching the given prefix and apply them to argv as though they were command line arguments.
Use the "__" separator in the environment variable to indicate nested options. (e.g. prefix_nested__foo => nested.foo)
If this method is called with no argument or with an empty string or with true,
then all env vars will be applied to argv.
Program arguments are defined in this order of precedence:
var argv = require('yargs')
.env('MY_PROGRAM')
.option('f', {
alias: 'fruit-thing',
default: 'apple'
})
.argv
console.log(argv)
$ node fruity.js
{ _: [],
f: 'apple',
'fruit-thing': 'apple',
fruitThing: 'apple',
'$0': 'fruity.js' }
$ MY_PROGRAM_FRUIT_THING=banana node fruity.js
{ _: [],
fruitThing: 'banana',
f: 'banana',
'fruit-thing': 'banana',
'$0': 'fruity.js' }
$ MY_PROGRAM_FRUIT_THING=banana node fruity.js -f cat
{ _: [],
f: 'cat',
'fruit-thing': 'cat',
fruitThing: 'cat',
'$0': 'fruity.js' }
Env var parsing is disabled by default, but you can also explicitly disable it
by calling .env(false), e.g. if you need to undo previous configuration.
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');
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.
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.
Method to execute when a failure occurs, rather than printing the failure message.
fn is called with the failure message that would have been printed, the
Error instance originally thrown and yargs state when the failure
occured.
var argv = require('yargs')
.fail(function (msg, err, yargs) {
if (err) throw err // preserve stack
console.error('You broke it!')
console.error(msg)
console.error('You should be doing', yargs.help())
process.exit(1)
})
.argv
Allows to programmatically get completion choices for any line.
args: An array of the words in the command line to complete.
done: The callback to be called with the resulting completions.
For example:
require('yargs')
.option('foobar')
.option('foobaz')
.completion()
.getCompletion(['./test.js', '--foo'], function (completions) {
console.log(completions)
})
Outputs the same completion choices as ./test.js --fooTAB: --foobar and --foobaz
Indicate that an option (or group of options) should not be reset when a command is executed, as an example:
var argv = require('yargs')
.option('a', {
alias: 'all',
default: true
})
.option('n', {
alias: 'none',
default: true
})
.command('foo', 'foo command', function (yargs) {
return yargs.option('b', {
alias: 'bar'
})
})
.help('help')
.global('a')
.argv
If the foo command is executed the all option will remain, but the none
option will have been eliminated.
help, version, and completion options default to being global.
Given a key, or an array of keys, places options under an alternative heading when displaying usage instructions, e.g.,
var yargs = require('yargs')(['--help'])
.help()
.group('batman', 'Heroes:')
.describe('batman', "world's greatest detective")
.wrap(null)
.argv
Heroes:
--batman world's greatest detective
Options:
--help Show help [boolean]
Add an option (e.g. --help) and implicit command that displays the usage
string and exits the process.
If present, the description parameter customizes the description of
the help option in the usage string.
If a boolean argument is provided, it will enable or disable the use of an
implicit command. The implicit command is enabled by default, but it can be
disabled by passing false.
Note that any multi-char aliases (e.g. help) used for the help option will
also be used for the implicit command. If there are no multi-char aliases (e.g.
h), then all single-char aliases will be used for the command.
If invoked without parameters, .help() will use --help as the option and
help as the implicit command to trigger help output.
Example:
var yargs = require("yargs")(['--help'])
.usage("$0 -operand1 number -operand2 number -operation [add|subtract]")
.help()
.argv
Later on, argv can be retrieved with yargs.argv.
Given the key x is set, it is required that the key y is set.
Optionally .implies() can accept an object specifying multiple implications.
Return the locale that yargs is currently using.
By default, yargs will auto-detect the operating system's locale so that yargs-generated help content will display in the user's language.
To override this behavior with a static locale, pass the desired locale as a string to this method (see below).
Override the auto-detected locale from the user's operating system with a static
locale. Note that the OS locale can be modified by setting/exporting the LC_ALL
environment variable.
var argv = require('yargs')
.usage('./$0 - follow ye instructions true')
.option('option', {
alias: 'o',
describe: "'tis a mighty fine option",
demand: true
})
.command('run', "Arrr, ya best be knowin' what yer doin'")
.example('$0 run foo', "shiver me timbers, here's an example for ye")
.help('help')
.wrap(70)
.locale('pirate')
.argv
./test.js - follow ye instructions true
Choose yer command:
run Arrr, ya best be knowin' what yer doin'
Options for me hearties!
--option, -o 'tis a mighty fine option [requi-yar-ed]
--help Parlay this here code of conduct [boolean]
Ex. marks the spot:
test.js run foo shiver me timbers, here's an example for ye
Ye be havin' to set the followin' argument land lubber: option
Locales currently supported:
To submit a new translation for yargs:
./locales/en.json as a starting point.The Microsoft Terminology Search can be useful for finding the correct terminology in your locale.
The number of arguments that should be consumed after a key. This can be a useful hint to prevent parsing ambiguity. For example:
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.
The key provided represents a path and should have path.normalize() applied.
Tell the parser to always interpret key as a number.
If key is an array, all elements will be parsed as numbers.
If the option is given on the command line without a value, argv will be
populated with undefined.
If the value given on the command line cannot be parsed as a number, argv will
be populated with NaN.
Note that decimals, hexadecimals, and scientific notation are all accepted.
var argv = require('yargs')
.number('n')
.number(['width', 'height'])
.argv
This method can be used to make yargs aware of options that could
exist. You can also pass an opt object which can hold further
customization, like .alias(), .demandOption() etc. for that option.
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')
.demandOption('f')
.default('f', '/etc/passwd')
.describe('f', 'x marks the spot')
.string('f')
.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
;
Valid opt keys include:
alias: string or array of strings, alias(es) for the canonical option key, see alias()array: boolean, interpret option as an array, see array()boolean: boolean, interpret option as a boolean flag, see boolean()choices: value or array of values, limit valid option arguments to a predefined set, see choices()coerce: function, coerce or transform parsed command line values into another value, see coerce()config: boolean, interpret option as a path to a JSON config file, see config()configParser: function, provide a custom config parsing function, see config()count: boolean, interpret option as a count of boolean flags, see count()default: value, set a default value for the option, see default()defaultDescription: string, use this description for the default value in help content, see default()demandOption: boolean or string, demand the option be given, with optional error message, see demandOption()desc/describe/description: string, the option description for help content, see describe()global: boolean, indicate that this key should not be reset when a command is invoked, see global()group: string, when displaying usage instructions place the option under an alternative group heading, see group()nargs: number, specify how many arguments should be consumed for the option, see nargs()normalize: boolean, apply path.normalize() to the option, see normalize()number: boolean, interpret option as a number, number()requiresArg: boolean, require the option be specified with a value, see requiresArg()skipValidation: boolean, skips validation if the option is present, see skipValidation()string: boolean, interpret option as a string, see string()type: one of the following strings
Parse args instead of process.argv. Returns the argv object.
args may either be a pre-processed argv array, or a raw argument string.
A context object can optionally be given as the second argument to parse(), providing a
useful mechanism for passing state information to commands:
const parser = yargs
.command('lunch-train <restaurant>', 'start lunch train', function () {}, function (argv) {
console.log(argv.restaurant, argv.time)
})
.parse("lunch-train rudy's", {time: '12:15'})
A parseCallback can also be provided to .parse(). If a callback is given, it will be invoked with three arguments:
err: populated if any validation errors raised while parsing.argv: the parsed argv object.output: any text that would have been output to the terminal, had a
callback not been provided.// providing the `fn` argument to `parse()` runs yargs in headless mode, this
// makes it easy to use yargs in contexts other than the CLI, e.g., writing
// a chat-bot.
const parser = yargs
.command('lunch-train <restaurant> <time>', 'start lunch train', function () {}, function (argv) {
api.scheduleLunch(argv.restaurant, moment(argv.time))
})
.help()
parser.parse(bot.userText, function (err, argv, output) {
if (output) bot.respond(output)
})
Note: Providing a callback to parse() disables the exitProcess setting until after the callback is invoked.
Similar to config(), indicates that yargs should interpret the object from the specified key in package.json
as a configuration object.
cwd can optionally be provided, the package.json will be read
from this location.
Should yargs provide suggestions regarding similar commands if no matching command is found?
An alias for demand(). See docs there.
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 behavior is to set the value of any key not followed by an
option value to true.
Reset the argument object built up so far. This is useful for creating nested command line interfaces. Use global to specify keys that should not be reset.
var yargs = require('yargs')
.usage('$0 command')
.command('hello', 'hello command')
.command('world', 'world command')
.demandCommand(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();
}
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.
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(); //prints to stderr using console.error()
Or, to print the usage data to stdout instead, you can specify the use of console.log:
yargs.showHelp("log"); //prints to stdout using console.log()
Later on, argv can be retrieved with yargs.argv.
By default, yargs outputs a usage string if any error is detected. Use the
.showHelpOnFail() method to customize this behavior. 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 -f <file>')
.demandOption('f')
.alias('f', 'file')
.describe('f', 'Load a file')
.string('f')
.showHelpOnFail(false, 'Specify --help for available options')
.help('help')
.argv;
// etc.
$ node line_count.js
Missing argument value: f
Specify --help for available options
Specifies either a single option key (string), or an array of options. If any of the options is present, yargs validation is skipped.
Any command-line argument given that is not demanded, or does not have a corresponding description, will be reported as an error.
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.
Override the default strings used by yargs with the key/value
pairs provided in obj:
var argv = require('yargs')
.command('run', 'the run command')
.help('help')
.updateStrings({
'Commands:': 'My Commands -->\n'
})
.wrap(null)
.argv
My Commands -->
run the run command
Options:
--help Show help [boolean]
If you explicitly specify a locale(), you should do so before calling
updateStrings().
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).
Add an option (e.g. --version) that displays the version number (given by the
version parameter) and exits the process.
If no arguments are passed to version (.version()), yargs will parse the package.json
of your module and use its version value. The default value of option is --version.
You can provide a function for version, rather than a string.
This is useful if you want to use a version stored in a location other than package.json:
var argv = require('yargs')
.version(function() {
return require('../lib/version').version;
})
.argv;
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 (no right-align). Use .wrap(yargs.terminalWidth()) to
maximize the width of yargs' usage instructions.
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' ],
a: 1,
b: 2,
'$0': 'examples/reflect.js' }
If you want to explicitly 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
{ _: [], a: true, b: false, '$0': 'examples/reflect.js' }
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
{ _: [], x: [ 5, 8, 0 ], '$0': 'examples/reflect.js' }
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
{ _: [],
foo: { bar: { baz: 33 }, quux: 5 },
'$0': 'examples/reflect.js' }
Short numeric -n5 style arguments work too:
$ node examples/reflect.js -n123 -m456
{ _: [], n: 123, m: 456, '$0': 'examples/reflect.js' }
With npm, just do:
npm install yargs
or clone this project on github:
git clone http://github.com/yargs/yargs.git
To run the tests with npm, just do:
npm test
Using the yargs stanza in your package.json you can turn on and off
some of yargs' parsing features:
{
"yargs": {
"short-option-groups": true,
"camel-case-expansion": true,
"dot-notation": true,
"parse-numbers": true,
"boolean-negation": true
}
}
See the yargs-parser module for detailed documentation of this feature.
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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