A light, featureful and explicit option parsing library for node.js.

Why another one? See below. tl;dr: The others I've tried are one of too loosey goosey (not explicit), too big/too many deps, or ill specified. YMMV.

Install

npm install dashdash

Active Versions

• 2.x - Version 2.x dropped support for node versions earlier than node 10.x. While I don't expect to actively break functionality, new changes are no longer tested on earlier versions.
• 1.x - This version supports back to node version 0.10.x.

Usage

var dashdash = require('dashdash');

// Specify the options. Minimally name (or names) and type
// must be given for each.
var options = [
    {
        // names or a single name. First element is the opts.KEY.
        names: ['help', 'h'],
        // See "Option specs" below for types.
        type: 'bool',
        help: 'Print this help and exit.'
    }
];
// Shortcut form. As called it infers process.argv. See below for
// the longer form to use methods like .help() on the Parser object.
var opts = dashdash.parse({options: options});
console.log("opts:", opts);
console.log("args:", opts._args);

Longer Example

A more realistic starter script "foo.js" is as follows. This also shows using

parser.help()

var dashdash = require('dashdash');

var options = [
    {
        name: 'version',
        type: 'bool',
        help: 'Print tool version and exit.'
    },
    {
        names: ['help', 'h'],
        type: 'bool',
        help: 'Print this help and exit.'
    },
    {
        names: ['verbose', 'v'],
        type: 'arrayOfBool',
        help: 'Verbose output. Use multiple times for more verbose.'
    },
    {
        names: ['file', 'f'],
        type: 'string',
        help: 'File to process',
        helpArg: 'FILE'
    }
];
var parser = dashdash.createParser({options: options});
try {
    var opts = parser.parse(process.argv);
} catch (e) {
    console.error('foo: error: %s', e.message);
    process.exit(1);
}
console.log("# opts:", opts);
console.log("# args:", opts._args);
// Use parser.help() for formatted options help.
if (opts.help) {
    var help = parser.help({includeEnv: true}).trimRight();
    console.log('usage: node foo.js [OPTIONS]\n'
                + 'options:\n'
                + help);
    process.exit(0);
}
// ...

Some example output from this script (foo.js):

$ node foo.js -h
# opts: { help: true,
  _order: [ { name: 'help', value: true, from: 'argv' } ],
  _args: [] }
# args: []
usage: node foo.js [OPTIONS]
options:
    --version             Print tool version and exit.
    -h, --help            Print this help and exit.
    -v, --verbose         Verbose output. Use multiple times for more verbose.
    -f FILE, --file=FILE  File to process

$ node foo.js -v
opts: { verbose: [ true ],
  _order: [ { name: 'verbose', value: true, from: 'argv' } ],
  _args: [] }
args: []
$ node foo.js --version arg1
opts: { version: true,
  _order: [ { name: 'version', value: true, from: 'argv' } ],
  _args: [ 'arg1' ] }
args: [ 'arg1' ]
$ node foo.js -f bar.txt
opts: { file: 'bar.txt',
  _order: [ { name: 'file', value: 'bar.txt', from: 'argv' } ],
  _args: [] }
args: []
$ node foo.js -vvv --file=blah
opts: { verbose: [ true, true, true ],
  file: 'blah',
  _order:
   [ { name: 'verbose', value: true, from: 'argv' },
     { name: 'verbose', value: true, from: 'argv' },
     { name: 'verbose', value: true, from: 'argv' },
     { name: 'file', value: 'blah', from: 'argv' } ],
  _args: [] }
args: []

See the "examples" dir for a number of starter examples using some of dashdash's features.

Environment variable integration

If you want to allow environment variables to specify options to your tool, dashdash makes this easy. We can change the 'verbose' option in the example above to include an 'env' field:

    {
        names: ['verbose', 'v'],
        type: 'arrayOfBool',
        env: 'FOO_VERBOSE',         // 
then the "FOO_VERBOSE" environment variable can be used to set this
option:
$ FOO_VERBOSE=1 node foo.js
# opts: { verbose: [ true ],
  _order: [ { name: 'verbose', value: true, from: 'env' } ],
  _args: [] }
# args: []

Boolean options will interpret the empty string as unset, '0' as false
and anything else as true.
$ FOO_VERBOSE= node examples/foo.js                 # not set
# opts: { _order: [], _args: [] }
# args: []

$ FOO_VERBOSE=0 node examples/foo.js                # '0' is false
opts: { verbose: [ false ],
  _order: [ { key: 'verbose', value: false, from: 'env' } ],
  _args: [] }
args: []
$ FOO_VERBOSE=1 node examples/foo.js                # true
opts: { verbose: [ true ],
  _order: [ { key: 'verbose', value: true, from: 'env' } ],
  _args: [] }
args: []
$ FOO_VERBOSE=boogabooga node examples/foo.js       # true
opts: { verbose: [ true ],
  _order: [ { key: 'verbose', value: true, from: 'env' } ],
  _args: [] }
args: []

Non-booleans can be used as well. Strings:
$ FOO_FILE=data.txt node examples/foo.js
# opts: { file: 'data.txt',
  _order: [ { key: 'file', value: 'data.txt', from: 'env' } ],
  _args: [] }
# args: []

Numbers:
$ FOO_TIMEOUT=5000 node examples/foo.js
# opts: { timeout: 5000,
  _order: [ { key: 'timeout', value: 5000, from: 'env' } ],
  _args: [] }
# args: []

$ FOO_TIMEOUT=blarg node examples/foo.js
foo: error: arg for "FOO_TIMEOUT" is not a positive integer: "blarg"

With the 
includeEnv: true
 config to 
parser.help()
 the environment
variable can also be included in help output:
usage: node foo.js [OPTIONS]
options:
    --version             Print tool version and exit.
    -h, --help            Print this help and exit.
    -v, --verbose         Verbose output. Use multiple times for more verbose.
                          Environment: FOO_VERBOSE=1
    -f FILE, --file=FILE  File to process

Bash completion

Dashdash provides a simple way to create a Bash completion file that you
can place in your "bashcompletion.d" directory -- sometimes that is
"/usr/local/etc/bashcompletion.d/"). Features:

• Support for short and long opts
• Support for knowing which options take arguments
• Support for subcommands (e.g. 'git log ' to show just options for the log subcommand). See node-cmdln for how to integrate that.
• Does the right thing with "--" to stop options.
• Custom optarg and arg types for custom completions.

Dashdash will return bash completion file content given a parser instance:

var parser = dashdash.createParser({options: options});
console.log( parser.bashCompletion({name: 'mycli'}) );

or directly from a

options

var code = dashdash.bashCompletionFromOptions({
    name: 'mycli',
    options: OPTIONS
});

Write that content to "/usr/local/etc/bash_completion.d/mycli" and you will have Bash completions for

mycli

You could add a

--completion

See examples/ddcompletion.js for a complete example, including how one can define bash functions for completion of custom option types. Also see node-cmdln for how it uses this for Bash completion for full multi-subcommand tools.

• TODO: document specExtra
• TODO: document includeHidden
• TODO: document custom types,

  function complete\_FOO

  guide, completionType
• TODO: document argtypes

Parser config

Parser construction (i.e.

dashdash.createParser(CONFIG)

• options

  (Array of option specs). Required. See the Option specs section below.

• interspersed

  (Boolean). Optional. Default is true. If true this allows interspersed arguments and options. I.e.:

  node ./tool.js -v arg1 arg2 -h   # '-h' is after interspersed args
  

Set it to false to have '-h' not get parsed as an option in the above example.

• allowUnknown

  (Boolean). Optional. Default is false. If false, this causes unknown arguments to throw an error. I.e.:

  node ./tool.js -v arg1 --afe8asefksjefhas
  

Set it to true to treat the unknown option as a positional argument.

Caveat: When a shortopt group, such as

-xaz

Consider if you have a known short option

-a

    node ./tool.js -xaz

where

-x

-z

1. `-x` takes a value: `{x: 'az'}`
2. `-x` and `-z` are both booleans: `{x:true,a:true,z:true}`

Since dashdash does not know what

-x

-z

{a:true,_args:['-x','-z']}

{x:'az'}

{_args:['-xaz']}

Option specs

Example using all fields (required fields are noted):

{
    names: ['file', 'f'],       // Required (one of `names` or `name`).
    type: 'string',             // Required.
    completionType: 'filename',
    env: 'MYTOOL_FILE',
    help: 'Config file to load before running "mytool"',
    helpArg: 'PATH',
    helpWrap: false,
    default: path.resolve(process.env.HOME, '.mytoolrc')
}

Each option spec in the

options

• name

  (String) or

  names

  (Array). Required. These give the option name and aliases. The first name (if more than one given) is the key for the parsed

  opts

  object.

• type

  (String). Required. One of:
  • bool
  • string
  • number
  • integer
  • positiveInteger
  • date (epoch seconds, e.g. 1396031701, or ISO 8601 format

    YYYY-MM-DD[THH:MM:SS[.sss][Z]]

    , e.g. "2014-03-28T18:35:01.489Z")
  • arrayOfBool
  • arrayOfString
  • arrayOfNumber
  • arrayOfInteger
  • arrayOfPositiveInteger
  • arrayOfDate

FWIW, these names attempt to match with asserts on assert-plus. You can add your own custom option types with

dashdash.addOptionType

• completionType

  (String). Optional. This is used for Bash completion for an option argument. If not specified, then the value of

  type

  is used. Any string may be specified, but only the following values have meaning:

  • none

    : Provide no completions.

  • file

    : Bash's default completion (i.e.

    complete -o default

    ), which includes filenames.
  • Any string FOO for which a

    function complete_FOO

    Bash function is defined. This is for custom completions for a given tool. Typically these custom functions are provided in the

    specExtra

    argument to

    dashdash.bashCompletionFromOptions()

    . See "examples/ddcompletion.js" for an example.

• env

  (String or Array of String). Optional. An environment variable name (or names) that can be used as a fallback for this option. For example, given a "foo.js" like this:

  var options = [{names: ['dry-run', 'n'], env: 'FOO_DRY_RUN'}];
  var opts = dashdash.parse({options: options});
  

Both

node foo.js --dry-run

FOO_DRY_RUN=1 node foo.js

opts.dry_run = true

An environment variable is only used as a fallback, i.e. it is ignored if the associated option is given in

argv

• help

  (String). Optional. Used for

  parser.help()

  output.

• helpArg

  (String). Optional. Used in help output as the placeholder for the option argument, e.g. the "PATH" in:

  ...
  -f PATH, --file=PATH    File to process
  ...
  

• helpWrap

  (Boolean). Optional, default true. Set this to

  false

  to have that option's

  help

  not be text wrapped in

  .help()

  output.

• default

  . Optional. A default value used for this option, if the option isn't specified in argv.

• hidden

  (Boolean). Optional, default false. If true, help output will not include this option. See also the

  includeHidden

  option to

  bashCompletionFromOptions()

  for Bash completion.

Option group headings

You can add headings between option specs in the

options

group

var options = [
    {
        group: 'Armament Options'
    },
    {
        names: [ 'weapon', 'w' ],
        type: 'string'
    },
    {
        group: 'General Options'
    },
    {
        names: [ 'help', 'h' ],
        type: 'bool'
    }
];
...

Note: You can use an empty string,

{group: ''}

Help config

The

parser.help(...)

    Options:
      Armament Options:
    ^^  -w WEAPON, --weapon=WEAPON  Weapon with which to crush. One of: |
   /                                sword, spear, maul                  |
  /   General Options:                                                  |
 /      -h, --help                  Print this help and exit.           |
/   ^^^^                            ^                                   |
\       `-- indent                   `-- helpCol              maxCol ---'
 `-- headingIndent

• indent

  (Number or String). Default 4. Set to a number (for that many spaces) or a string for the literal indent.

• headingIndent

  (Number or String). Default half length of

  indent

  . Set to a number (for that many spaces) or a string for the literal indent. This indent applies to group heading lines, between normal option lines.

• nameSort

  (String). Default is 'length'. By default the names are sorted to put the short opts first (i.e. '-h, --help' preferred to '--help, -h'). Set to 'none' to not do this sorting.

• maxCol

  (Number). Default 80. Note that reflow is just done on whitespace so a long token in the option help can overflow maxCol.

• helpCol

  (Number). If not set a reasonable value will be determined between

  minHelpCol

  and

  maxHelpCol

  .

• minHelpCol

  (Number). Default 20.

• maxHelpCol

  (Number). Default 40.

• helpWrap

  (Boolean). Default true. Set to

  false

  to have option

  help

  strings not be textwrapped to the helpCol..maxCol range.

• includeEnv

  (Boolean). Default false. If the option has associated environment variables (via the

  env

  option spec attribute), then append mentioned of those envvars to the help string.

• includeDefault

  (Boolean). Default false. If the option has a default value (via the

  default

  option spec attribute, or a default on the option's type), then a "Default: VALUE" string will be appended to the help string.

Custom option types

Dashdash includes a good starter set of option types that it will parse for you. However, you can add your own via:

var dashdash = require('dashdash');
dashdash.addOptionType({
    name: '...',
    takesArg: true,
    helpArg: '...',
    parseArg: function (option, optstr, arg) {
        ...
    },
    array: false,  // optional
    arrayFlatten: false,  // optional
    default: ...,   // optional
    completionType: ...  // optional
});

For example, a simple option type that accepts 'yes', 'y', 'no' or 'n' as a boolean argument would look like:

var dashdash = require('dashdash');

function parseYesNo(option, optstr, arg) {
    var argLower = arg.toLowerCase()
    if (['yes', 'y'].indexOf(argLower)) {
        return true;
    } else if (['no', 'n'].indexOf(argLower)) {
        return false;
    } else {
        throw new Error(format(
            'arg for "%s" is not "yes" or "no": "%s"',
            optstr, arg));
    }
}
dashdash.addOptionType({
    name: 'yesno'
    takesArg: true,
    helpArg: '',
    parseArg: parseYesNo
});
var options = {
    {names: ['answer', 'a'], type: 'yesno'}
};
var opts = dashdash.parse({options: options});

See "examples/custom-option-*.js" for other examples. See the

addOptionType

Why

Why another node.js option parsing lib?

• nopt

  really is just for "tools like npm". Implicit opts (e.g. '--no-foo' works for every '--foo'). Can't disable abbreviated opts. Can't do multiple usages of same opt, e.g. '-vvv' (I think). Can't do grouped short opts.

• optimist

  has surprise interpretation of options (at least to me). Implicit opts mean ambiguities and poor error handling for fat-fingering.

  process.exit

  calls makes it hard to use as a library.

• optparse

  Incomplete docs. Is this an attempted clone of Python's

  optparse

  . Not clear. Some divergence.

  parser.on("name", ...)

  API is weird.

• argparse

  Dep on underscore. No thanks just for option processing.

  find lib | wc -l

  ->

  26

  . Overkill. Argparse is a bit different anyway. Not sure I want that.

• posix-getopt

  No type validation. Though that isn't a killer. AFAIK can't have a long opt without a short alias. I.e. no

  getopt_long

  semantics. Also, no whizbang features like generated help output.

• "commander.js": I wrote a critique a while back. It seems fine, but last I checked had an outstanding bug that would prevent me from using it.

License

MIT. See LICENSE.txt.