0.1.0 (2012-06-13)

An command line interface (CLI) argument parser that is:

  • POSIX “Utility Argument Syntax” compliant
  • Unobtrusive - Does not mandate flow control, does not print to STDOUT on your behalf, and does not magically manage --help
  • Ambiguity aware - lets you specify how to handle ambiguities such as -bar, which can mean both -b -a -r and -b=ar.
var pap = require("posix-argv-parser");
var args = pap.create();
var v = pap.validators;

args.createOption(["-p", "--port"], {
    // All options are optional

    // Implies hasValue: true, which allows parser to read -p2345 as -p=2345
    defaultValue: 8282,

    // Both built-in and custom validations supported,
    // synchronous as well as asynchronous (promise based)
    validators: [v.integer("Custom message. ${1} must be a number.")],

    // Transforms allow you to get more intelligent values
    // than raw strings back
    transform: function (value) { return parseInt(value, 10); }

args.createOption(["-v"], {
    validators: [function (opt) {
        // See also asynchronous validators
        if (opt.timesSet < 1) {
            throw new Error("Set " + opt.signature + " at least once!");

// Operands are statements without options.
// Example: the path in `mything --port=1234 path/to/stuff`
args.createOperand("rootPath", {
    // Used in error msgs
    signature: "Presentation root directory",
    // Both will use default error messages
    validators: [v.file(), v.required()]

posixArgvParser.parse(process.argv.slice(2), function (errors, options) {
    if (errors) { return console.log(errors[0]); }

    // Various useful ways to get the values from the options.
    // Will be a true number thanks to the transform


var args = require("posix-argv-parser").create();

Creates a new instance of posix-argv-parser that holds a collection of options and operands.

posixArgvParser.createOption(flags[, options])
args.createOption(["-h", "--help"]);

Creates a new option. An option has all the properties of an argument, as well as option.hasValue and option.timesSet. The options object is optional.

posixArgvParser.addShorthand(opt[, argv1, ...])

A shorthand is a convenience method for adding options to your CLI that simply set other options.

args.createOption("--env", { hasValue: true });
args.addShorthand("--dev", ["--env", "dev"]);
args.addShorthand("--prod", ["--env", "prod"]);

This makes passing --dev an equlvalent to passing --env dev.

posixArgvParser.createOperand([name][, options])

Creates a new operand. An operand has all the properties of an argument, as well as greedy: true|false - i.e. whether or not it will eat many arguments or just one (defaults to false, just one). The name is optional, and should be a string. The name is used to access the value through the options object passed to the parse callback. If not provided, it defaults to “OPD” (beware when using more than one operand).

posixArgvParser.parse(args, callback)

Performs parsing and validation of argv. In Node.JS, make sure to discard the first two items of process.argv, as they contain unrelated arguments (“node” and the file name).

The callback is called with two arguments, errors, which is either undefined, or an array of errors and/or validation messages, and an options object, which is used to retrieve data from configured options.

var args = require("posix-argv-parser").create();
args.handle(process.argv.slice(2), function (errors, options) {
    if (errors) {
        // Print an error msg, i.e. console.log(errors[0])
    // Continue with normal operation. I.e. options["-v"].hasValue,
    // options["-v"].timesSet, options["-p"].value, etc.

Arguments (options and operands)

Options and operands are the two types of arguments handled by posix-argv-parser, and they share common functionality, listed below this introduction.

An option is a flag, with or without a value. -p, -p abc, -pabc, -p=abc, --port abc and --port=abc are all supported by posix-argv-parser.

-pabc can mean both -p -a -b -c and -p=abc. posix-argv-parser uses opt.hasValue to separate the two. With opt.hasValue set to true, -pabc will be handled as -p=abc. When false (default), it will be handled as -p -a -b -c. In that case you also need to have option handlers for -a, -b and -c, or you’ll get a validation error such as "unknown option -a" (depending on which option posix-argv-parser first encountered that didn’t exist).

An operand is an option-less value, i.e. foo (with no -b or --myopt prefixing it). It’s commonly used for arguments that always have to be passed. Examples are nano path/to/file.txt, git checkout master, rmdir my_dir, etc. The validators validators.file(), validators.directory(), and validators.fileOrDirectory() are very useful for operands.

Note that the parser can handle a mix and match of options and operands in any order, i.e. mycommand --port 1234 my/directory and mycommand my/directory --port 1234 will both work.

Multiple operands will be applied in order of creation. I.e. mycommand something with two operands will assign "something" to the first and undefined to the second, unless the first is greedy, in which case it will receive all the operand values.

See example usage at the beginning of this document for more information.

When creating options and operands, the following properties can be passed in with the “options” object.


An array of validators. A validator is a function that accepts the argument result object as input. See below for a description of argument result objects. To fail validation, the validator can either throw an error, or return a rejecting promise.


A function that transforms the raw string value provided before assigning it to the opt.value property of an argument result object. The function receives the string value as input, and should return any value back.


If the argument takes a value, set to true. Defaults to false for options, is always true for operands (thus it can be omitted).


The default value to use if the argument was not provided. When opt.defaultValue is provided, opt.hasValue is implied and can be omitted. The default value should be a string, and will be validated and transformed like actual values.


The signature is used to identify options and operands in validation errors. Options automatically gets a signature consisting of the option flags assigned to it:

var opt = args.createOption(["-v", "--version"]);
opt.signature; // "-v/--version"
opt.signature = "-v"; // custom signature

Specifying a signature is more useful for operands, since an operand doesn’t have any data that it can use to auto generate a signature (their default signature is “OPD”):

var rootDir = args.createOperand();
rootDir.signature; // "OPD", as the default name
rootDir.signature = "Root directory";


Options has additional properties that operands doesn’t have.


Only makes sense if opt.hasValue is true. When this property is false, an option can both be provided as a flag with no value or as an option with a value.

A common example of options that work with and without values are help options, that may be provided alone to get general help, e.g. mything –help, and with values to get help for specific topics, e.g. mything –help bisect.

Argument result

Argument result objects are produced when calling args.parse() to parse argv into the predefined options and operands. There is one result object per original option/operand. These objects have the following properties:


true or false depending on whether or not the argument was present in argv.


The value of the argument. Is normally a string, but may be any object if the argument had a transform function.


The number of times an argument was set. Useful for options like -v (verbose) which you might want to allow setting multiple times, giving the user more and more verbose output from your program:

-v // 1
-vv // 2
-v -v -v -v // 4
-v -vv -vv -vvv // 8


Validators let you add requirements with associated error messages to options and operands.

posix-argv-parser has a number of built-in validators, and creating custom ones is dead simple, as a validator is just a function.

Built-in validators

The built in validators provides a selection of generic validators. You can customize the error messages by passing strings with tokens like "${1}" in them. The number and value maps are documented for each validator.

Validators are functions, yet the built-in validators are used by calling them directly with custom error messages. This works because the built-in validators all return the actual validation function.

// Uses built-in error message

// Specify your own error message
posixArgvParser.validators.required("${1} has to be set");

Fails if the option is not set.

Custom error message:

The option opt.signature

Will fail validation if the option was not an integer, i.e. "foo" and 42.5.

Custom error message:

The specified number
The option opt.signature

Will fail validation if the option was not a number, i.e. "foo" and ?.

Custom error message:

The specified number
The option opt.signature

Will fail validation if the option was not a path pointing to an existing file in the file system.

Custom error message:

The specified file
The option opt.signature

Will fail validation if the option was not a path pointing to an existing directory in the file system.

Custom error message:

The specified directory
The option opt.signature

Will fail validation if the option was not a path pointing to an existing file or directory in the file system. Will fail for block devices, sockets, et c.

Custom error message:

The specified file or directory
The option opt.signature

Custom validators

A validator is a function that throws an error or returns a promise. If it does not do any of those things, it is immediately considered passed. The function is passed an argument result object.

args.createOption("-v", {
    validators: [function (opt) {
        if (opt.value == "can not be this value") {
            throw new Error("This is the error message.");

Promises are used to facilitate asynchronous validators. Here’s an example of a validator that checks if a file is larger than 1MB:

var when = require("when");
args.createOption(["-f"], {
    validators: [function (opt) {
        var deferred = when.defer();
        fs.stat(opt.value, function (err, stat) {
            if (err) { deferred.reject("Unknown error: " + err); }

            if (stat.size > 1024) {
                deferred.reject(opt.value +
                    " (" + opt.signature + ") was larger than 1MB");
            } else {
        return deferred.promise;

Given --myopt /path/to/file and the file is larger than 1MB, you’ll get the error message "/path/to/file (--myopt) was larger than 1MB".

Rejecting the promise counts as an error. The first argument should be a string, and is the error message. (TODO: This will likely change to an error object with a message property).


Transforms can mutate the values of options. A transform is a simple function that receives the raw string value as input, and can return whatever it likes.:

args.createOption(["-p"], {
    transform: function (value) { return parseInt(value, 10); }


Types are predefined “options” objects that you can pass when creating options and/or operands. For instance, the “number” type includes the number validator, sets opt.hasValue to true, and includes a transform that converts the raw string to an actual number (by way of parseFloat):

args.createOption(["-n"], args.types.number());

Note that the type is a function call - it returns the options object. You can pass in additional options. The following example piggy-backs the number type to create an option that only takes positive numbers:

args.createOption(["-n"], args.types.number({
    validators: [function (opt) {
        if (parseFloat(opt.value) < 0) {
            throw new Error("Oh noes, negative number!");

Providing --help

It’s not in the nature of posix-argv-parser to automatically handle --help for you. It is however very easy to add such an option to your program. To help you keep all CLI option data in one place, options and operands are allowed to have a opt.description property that posix-argv-parser does not care about:

var args = require("posix-argv-parser").create();

args.createOption(["--port"], {
    defaultValue: 1234
    description: "The port to start the server on."

args.createOption(["-v"], {
    description: "Level of detail in output. " +
        "Pass multiple times (i.e. -vvv) for more output."

args.createOption(["--help", "-h"], { description: "Show this text" });
help.helpText = "Show this text";

args.parse(process.argv.slice(2), function (errors, options) {
    if (errors) { return console.log(errors[0]); }

    if (options["-h"].isSet) {
        args.options.forEach(function (opt) {
            console.log(opt.signature + ": " + opt.description);
    } else {
        // Proceed with normal program operation