Clop (Command Line Options Parser)

Clop is a utility for parsing commands and arguments for command-line "swiss-army" style programs. These are programs like "git" or "p4" that themselves just gateways to a set of commands with similar options. It also prints out an auto-formatted "help" document.

To use Clop, you supply a "command-line-interface" definition (a "cli") as a plain JavaScript object and ask clop to create an ArgParser. You then pass the system command line to the ArgParser's "parse" method, which returns an object specifying the command and the options supplied in a convenient form.

Some nice features of Clop include

• Default commands
• Optional arguments
• Option aliases
• Numeric arguments
• List arguments
• Enumeration arguments
• Argument validators

Command-line conventions

Clop imposes some opinionated conventions on command line arguments and options.

Example command line:

For the rest of this README, assume we are making a command-line utility called "tasker" for managing tasks. Here is a sample "tasker" command invocation to create an important cake baking task for user mickey of duration 2 hours:

$ tasker add -u mickey -important -hours 2 -d "Bake a cake"

Commands

The first argument is the "command." If the cli specifies a default command, the command may be omitted. The command is never prefixed with a dash. In the example above, the command is "add." Everything else is options.

Options

• Option order never matters.
• All options begin with a single dash whether they are abbreviations or not. (Double dashes are permitted but they are converted to single-dashes.)
• Options may have "aliases" which are all considered equivalent. Frequently there will be a long and short (single character) alias.
• Options may or may or may not take arguments
  • Arguments may specify type
  • Arguments can specify if they are multi-valued

Dashes, underscores, and mixedCase

Because dashes, underscores and mixedCase are all possible ways to specify concatenated terms, they are considered to be the same. Commands are not case-sensitive. TODO: I think this is a lousy idea. I'm going to get rid of it...

Install

$ npm install --save clop

Getting Started

At the top of your main program, import or require clop:

const clop = require('clop'); // es5

or

import clop from 'clop'; // es6

Create a JavaScript object that contains the description of the interface. The object should have the following structure:

const cli = {
    commands: [], // Array of Command objects detailing the names and descriptions of commands
    options: [], // Array of Options objects with their aliases, arguments, defaults and descriptions
    usage: '', // A string documenting basic usage of the program
    examples: '' // A string showing sample usages of the program
}

You will usually want to make the cli specification into its own JavaScript module to keep it separate from the rest of the code.

Command objects

Command objects have the following form:

{
    command: 'name', // The name of the command
    desc: 'Describe it', // The description of the command in help text
    default: true // Optional, defaults to 'false.' If set true, this command will be assumed if when command is specified
}

Options objects

Options objects have the following form:

{
    aliases: ['long', 'l'], // All the names the option can go by. The first one will be used as the key in the opts object, so make it the primary, non-abbreviated alias
    args: '<arg>', // Optional. Used in help text and error messages to refer to the argument(s) of the option. Does not name the option in the resulting opts object.
    desc: 'Describe it', // The description of the command in help text
    values: ['one', 'two', 'three'], // Optional. Describes the allowable values of the argument
    default: 'defaultValue' // Optional. A default argument to the option if none is specified or the option is absent
}

Create an ArgParser

Then create an ArgParser object with your cli:

const argParser = clop.createArgParser(cli); 

At this point the parser can be configured for special cases, but usually it doesn't have to be. Then parse the command line with the argParser and use the results:

const programSpec = argParser.parse(process.argv);
// programSpec.command now contains the "command" the user specified
// programSpec.opts now contains all of the options the user specified

Generating the "help" text

The "help" command or option is something of a special case because its entire function is to print out some text and quit the program. Therefore the parse method prints help and exits by default if it determines that the command is really "help." There are several ways that parse may determine that the command is "help."

Ways to invoke "help"

• Unless a cli specifies a default command, if the user does not specify a command, "parse" will assume that the user needs help.
• By default all parsers add a help option "-help" or "-h" to the cli. If you want to turn it off you need to configure the argParser before calling parse. Therefore by default if "-h" or "-help" appears among any other options, parse will print help text and exit.

argParser.configure({ omitDefaultHelpOption: true });

Since it is annoying to try to test a system that explictly exits, you can override both the printing and exiting behaviors of parse with the following configuration:

argParser.configure({ reportHelpContent: true });

If you specify this, in a case where parse invokes help, the programSpec will be returned as follows:

{
    command: 'help',
    helpContent: '<The full formatted help content>'
    opts: {<Any other opts specified>}
}

Error handling

In a case where a user makes a mistake like trying to refer to an unknown command or option, the default is to issue an informative error message to the console and exit. If you'd like to override this behavior specify a configuration parameter errorHandler as described below in Configuration parameters.

Configuration parameters

You can configure an argParser before calling parse by passing in a configuration object to its configure method. You can also pass this configuration object in to the clop.createArgParser(cli, config) method as an optional second parameter following the cli.

const argParser = clop.createArgParser(cli, {<config>});

or

argParser.configure({<config>});

The legal configuration options are

• errorHandler: A function that will be called with two arguments: a string error ID and full error text instead of having errors reported to the console and the program terminated. If this option is specified but the value is empty or is not a function, the errors will be silently added to the programSpec as an error object with string fields id and msg. Silent erroring is primarily useful for testing.
• reportHelpContent: Set this to true to return help content rather than report help to the console and exit.

TODO

Things that don't yet work include

• Command-less programs
• Subcommands
• Per-command help
• Per-command options
• Special "Flag" option type for booleans only

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

Authors

• Simon Greenwold - Clop

See also the list of contributors who participated in this project.

License

This project is licensed under the ISC License