NixClap

Simple, lightweight, flexible, and comprehensive Un*x Command Line Argument Parsing for NodeJS.

Features

• Lightweight with minimal dependencies.
• Comprehensive and flexible parsing capabilities similar to conventional Un*x parsing.
• Flexible handling of options and commands that can take variadic params.
• A simple and straightforward JSON interface for specifying options and commands.
• Very informative result that tells you where each option came from.
• Webpack friendly - allows bundling your cli into a single JS file with webpack.

Examples

Options only:

const NixClap = require("nix-clap");

const options = {
  names: {
    desc: "specify names",
    alias: ["n", "m"],
    type: "string array"
  }
};

const parsed = new NixClap()
  .version("1.0.0")
  .usage("$0 [options]")
  .init(options)
  .parse();

console.log("names", parsed.opts.names);

With commands:

const NixClap = require("nix-clap");

const options = {
  verbose: {
    desc: "enable verbose mode",
    alias: "v",
    type: "boolean",
    default: false
  }
};

const commands = {
  compile: {
    desc: "run compile on the files",
    args: "<string files...>",
    exec: parsed => {
      console.log("compile", parsed.args.files, "verbose", parsed.opts.verbose);
    }
  }
};

const parsed = new NixClap()
  .version("1.0.0")
  .usage("$0 [options] <command> [options]")
  .init(options, commands)
  .parse();

version, help, and usage must be called before init

Usage:

$ my-prog compile --verbose file1.jsx file2.jsx file3.jsx

More Examples

See examples folder for more working samples.

Parsing Capabilities

Options

Example: prog -xazvf=hello --foo-option hello bar -. --enable-blah

• Support - single char options or -- long form options.
• Options can have aliases.
• Both option forms can have argument specified with = or space.
  • ie: long form --foo-option=bar or --foo-option bar
  • ie: short form -f=bar or -f bar
• Both option forms can have variadic array args.
  • ie: --foo-option hello bar or -f hello bar
  • array args can have an optional type
• - options can be compounded, like -xazvf.
  • Last char can have args, like -xazvf=hello or -xazvf hello.
  • Other chars are treated as boolean options automatically.
• Variadic array args are terminated by any other options such as -x or --xyz, or explicitly with -. or --.
  • ie: cmd1 arg1 arg2 --some-array abc def ghi -. cmd2 arg1 arg2.
• Allow arbitrary unknown options but with arguments specified through = only.
  • Since it's ambiguous whether to take a non-option arg following an unknown option as an argument or a command.
• Counting number of option occurrences.
• Boolean option can be negated with --no- prefix.
• Allow custom value type coercions with a function or RegExp.

Commands

Example: prog sum 1 2 3 4

• Commands can have optional or required arguments.
  • Each argument type defaults to string, but can have an optional type
• Commands can have aliases.
• Possible to specify multiple commands.
• Commands can have variadic array arguments.
• Variadic array args are terminated by any other options such as -x or --xyz, or explicitly with -. or --.
  • ie: prog order pizza soda -. pickup (specifies two commands: order and pickup)
• Command can have its own options that are binded to it only.
• Top level options can be binded to specific commands only.
• Unbind top level options can be specified before or after commands.
• Allow arbitrary unknown commands that do not have arguments.
• Allow multiple custom value type coercions for each command.

Terminating and Resuming

• -- terminates parsing, with remaining args returned in parsed._.
• Parsing can be resumed after it's terminated.
• -. or --. can terminate variadic params for commands and options.

Install

npm i nix-clap --save

Interface

This module exposes a class with a few methods.

See APIs for more details.

options spec

const options = {
  "some-option": {
    alias: ["s", "so"],
    type: "string",
    desc: "description",
    default: "foo",
    require: true,
    requireArg: true,
    allowCmd: ["cmd1", "cmd2"]
  },
  "another-option": {}
};

Where:

field	description
alias	Specify aliases for the option, as a single string or an array of strings.
type	Type of argument for the option, one of: string, number, float, boolean, array, count, or coercion
	array can set type of elements as one of string, number, float, boolean like this: number array or float array
desc	Description for the option - a string or a function that returns string.
default	Default value to use for argument
require	true/false whether this option must be specified.
requireArg	true/false whether argument for the option is required.
allowCmd	list of command names this option is allow to follow only.

commands spec

const commands = {
  cmd1: {
    alias: ["c"],
    args: "<arg1> [arg2..]",
    usage: "$0 $1",
    desc: "description",
    exec: argv => {},
    default: true,
    options: {}
  },
  cmd2: {}
};

Where:

field	description
alias	Specify aliases for the command, as a single string or an array of strings.
args	Specify arguments for the command. <> means it's required and [] optional. See rules for more info.
usage	usage message when help for the command is invoked - a string or a function that returns a string.
	$0 will be replaced with program name and $1 with command name.
desc	Description for the command - can be a string or a function that returns a string.
exec	The callback handler for the command - see here for more details.
default	If true, set the command as default, which is invoked when no command was given in command line.
	- Only one command can be default.
	- Default command cannot have required args and must have the exec handler
options	List of options arguments private to the command. Follows the same spec as top level options

Rules for Command args

Rules for when specifying args for the command:

• all required args must be before optional args
• last one can specify variadic args with .., like <names..> or [names..]
• If you just want to get the list of args without naming it, you can specify with <..> or [..]
• named args can have an optional type like <number value> or [number values..]
  • supported types are number, float, string, boolean, or coercion

Value Coercion

If none of the predefined types work for you, you can specify your own as a function or a RegExp, or any value.

You use any valid identifier for the value type, and then you define a field with the same name in your spec that can be:

• function - will be called with the value to convert
• RegExp - will be used to match the value. undefined is returned if it didn't match.
• Anything else - will be used as the converted value.

For example:

const options = {
  customFn: {
    type: "fnval",
    fnval: value => {
      return value.substr(0, 1);
    }
  },
  customRegex: {
    type: "rx",
    rx: /^test$/i
  },
  customAny: {
    type: "foo",
    foo: "bar"
  }
};

const commands = {
  foo: {
    args: "<type1 value1> <type2 value2>",
    type1: value => `test-${value}`,
    type2: /^test$/i
  }
};

Parse Result

Use the method parse to parse command line arguments. It will return a parse result object.

{
  source: {},
  opts: {},
  verbatim: {},
  commands: [],
  index: 5,
  error,
  _: [],
  argv: []
}

Where:

• index - the index in argv parse stopped
• error - If parse failed and your parse-fail event handler throws, then this will contain the parse error. See skip default event behaviors for more details.
• source, opts, verbatim - objects containing info for the options. See details here
• commands - array of parsed command objects. See commands for more details.
• argv - original array of argv
• _ - remaining args in the argv array in case parsing was terminated by --.

If any command with exec handlers were specified, then parse will invoke them before returning the parse result object.

Parse Result source and opts objects

• opts - contains actual value for each option

• source - contains info about where the option value came from

  • cli - option specified by user in the command line
  • default - default value in your options spec
  • user - values you applied by calling the applyConfig method

• verbatim - contains original unprocessed value as given by the user in the command line

  • This is an array of values if there was actual values from the user
  • If there's no explicit value (ie. boolean or counting options), then this doesn't contain a field for the option.
  • If it's a boolean but the user specified with --no- prefix, then this contains a field with the value ["no-"]

For example, with the following conditions:

1. User specified --foo-bar=test in the command line
2. You have an option fooDefault with default value bar
3. You called applyConfig with applyConfig({fooConfig: 1, fooBar: "oops"}, parsed)

You would get the following in the parse result object:

{
  source: {
    fooBar: "cli",
    fooDefault: "default",
    fooConfig: "user"
  },
  opts: {
    fooBar: "test",
    fooDefault: "bar",
    fooConfig: 1
  },
  verbatim: {
    fooBar: ["test"]
  }
}

Note that the value oops for fooBar passed to applyConfig is not used since user's specified value is used.

Parse Result commands object

The commands object is an array of parsed commands:

{
  commands: [
    {
      name: "cmdName",
      long: "cmdName",
      unknown: false,
      args: {
        foo: "bar",
        variadic: ["a", "b"]
      },
      argList: ["bar", "a", "b"],
      opts: {},
      source: {},
      verbatim: {}
    }
  ];
}

• name is the name of the command used by the user in the command line that could be an alias
• long is the original form of the command name (not the alias)
• unknown - true if the command is not known
• args - the processed named arguments
• argList - list of all the arguments in unprocessed string form
• opts, source, verbatim - info for the options private to the command

Command exec handler

If the command has an exec handler, then it will be called with two arguments:

exec(result, parsed);

• First one is the object for the command
• Second one is the overall parsed object

Info about the command object:

{
  name: "cmdName",
  long: "cmdName",
  args: {
    foo: "bar",
    variadic: [ "a", "b" ]
  },
  argList: [ "bar", "a", "b" ],
  opts: {},
  source: {},
  verbatim: {}
}

Where opts and source contain both the command's private options and top level options.

You can turn this off with the skipExec config flag passed to NixClap constructor

Events

NixClap emits these events:

• help - when --help is invoked, emitted with the parse result object.
• pre-help - before output for --help
• post-help - after output for --help
• help - when --help is invoked, emitted with the parse result object.
• version - when --version is invoked, emitted with the parse result object.
• parsed - when all parsing is done but before command exec are invoked, emitted with { nixClap, parsed } where nixClap is the NixClap instance.
• parse-fail - when parse failed, emitted with parse result object, which has error field.
• unknown-option - when an unknown option is found, emitted with option name
• unknown-command - when an unknown command is found, emitted with command context, which has name field.
• no-action - when you have commands with exec and user specified no command that triggered an exec call.
• exit - When program is expected to terminate, emit with exit code.

Default Event Handlers

NixClap has default handlers for these events:

• help - Output help and emit exit
• version - If version has been set, then output version and emit exit.
• parse-fail - Output help and error message, and emit exit.
• unknown-option - Throws Error Unknown option ${name}
• unknown-command - Throws Error Unkown command ${ctx.name}
• no-action - Output help with error No command given and emit exit
• exit - calls process.exit(code)

Skip Default Event Behaviors

You can remove the default event handlers with one of these approaches:

• With the removeDefaultHandlers method.
• By passing in handlers object in the config for the constructor.

For example, using removeDefaultHandlers:

const nc = new NixClap().init(options, commands);
const parsed = nc.removeDefaultHandlers("parse-fail").parse();
if (parsed.error) {
  // handle the parse error here
}

Using constructor config.

const parsed = new NixClap({ handlers: { "parse-fail": false } }).parse();
if (parsed.error) {
  // handle the parse error here
}

APIs

These are methods NixClap class supports.

• NixClap
• Features
• Examples
  • More Examples
• Parsing Capabilities
  • Options
  • Commands
  • Terminating and Resuming
• Install
• Interface
  • options spec
  • commands spec
    • Rules for Command args
  • Value Coercion
  • Parse Result
    • Parse Result source and opts objects
    • Parse Result commands object
    • Command exec handler
  • Events
    • Default Event Handlers
      • Skip Default Event Behaviors
  • APIs
    • constructor(config)
    • version(v)
    • help(setting)
    • usage(msg), cmdUsage(msg)
    • init(options, commands)
    • parse(argv, start, parsed)
    • parseAsync(argv, start, parsed)
    • showHelp(err, cmdName)
    • removeDefaultHandlers()
    • applyConfig(config, parsed, src)
    • runExec(parsed, skipDefault)
    • runExecAsync(parsed, skipDefault)
• Others

constructor(config)

config is object with:

• name - set the program name. Will auto detect from process.argv if not specified.
• version - set the program version. Can also set with version method.
• help - custom help option setting. Can also set with help method.
• usage - usage message. Can also set with usage method.
• cmdUsage - generic usage message for commands. Can also set with cmdUsage method.
• skipExec - If true, will not call command exec handlers after parse.
• skipExecDefault - if true, will not call default command exec handler after parse.
  • In case you need to do something before invoking the exec handlers, you can set these flags and call the runExec(parsed, skipDefault) method yourself.
• output - callback for printing to console. Should take string as param. Default to calling process.stdout.write
• handlers - custom event handlers.

The handlers object can specify a function for each of the events or set it to false to turn off the default handler.

For example, this config will replace handler for parse-fail and turn off the default unknown-option handler.

const nc = new NixClap({
  handlers: {
    "parse-fail": (parsed) => { ... },
    "unknown-option": false
  }
});

version(v)

Set program version with a string. ie: 1.0.0

Return: The NixClap instance itself.

Must be called before the init method.

help(setting)

Set a custom option setting for invoking help. Default is:

Return: The NixClap instance itself.

{
  alias: "h",
  desc: "Show help"
}

Option name is always help. Call help(false) to turn off the default --help option.

Must be called before the init method.

usage(msg), cmdUsage(msg)

Set usage message for the program or command, which can be override by individual command's own usage.

msg format is any string. $0 will be replaced with program name and $1 with command name.

Return: The NixClap instance itself.

Must be called before the init method.

init(options, commands)

Initialize your options and commands

Return: The NixClap instance itself.

parse(argv, start, parsed)

Parse command line. Call without any params to parse process.argv.

Return: The parse result object.

• argv - array of CLI args. Defaults to process.argv.
• start - index for argv from where to start parsing
• parsed - previous result from parse. If passed, then parsing will add new data to it.

parseAsync(argv, start, parsed)

async version of parse.

• It will use runExecAsync to invoke command exec handlers serially.
• The command handler can return a Promise, which will be awaited.

Return: A promise the resolve with the parse result object.

showHelp(err, cmdName)

Show help message and then emit exit.

• err - if valid, then err.message will be printed after help message and exit with code 1.
• cmdName - if valid, then will print help for the specific command.

removeDefaultHandlers()

Remove NixClap's default handlers for the list of event names.

If you've replaced the handler through specifying handlers in config for the constructor, then this will not remove your handler.

Return: The NixClap instance itself.

• You can pass in "*" to remove all default handlers.
• You can pass in the event names you want to remove.

ie:

nc.removeDefaultHandlers("parse-fail", "unknown-option", "unknown-command");

applyConfig(config, parsed, src)

Allow you to apply extra config to the parsed object, overriding any opts with source not equal to cli.

For example, you can allow user to specify options in their package.json file, and apply those after the command line is parsed.

• config - Config object containing user options config
• parsed - The parse result object from NixClap.
• src - String, source to set if override. Default to user

Example on applying user config from package.json:

const pkg = require(path.resolve("package.json"));
const parsed = nc.parse();
nc.applyConfig(pkg.cliConfig, parsed);

runExec(parsed, skipDefault)

Go through the commands in parsed and call their exec handler.

The parse method will call this at the end unless skipExec flag is set.

Return: The number of commands with exec was invoked.

• parsed - The parse result object.
• skipDefault - boolean, if true then do not invoke default command's exec handler when no command with exec handler was given.

runExecAsync(parsed, skipDefault)

async version of runExec

Return: A promise that resolve with the number of commands with exec invoked.

Others

• argparse
• yargs
• commander
• optimist
• clap
• clap.js