clipanion

What is clipanion?

The clipanion npm package is a powerful library for building command-line interfaces (CLIs) in Node.js. It provides a rich set of features for defining commands, parsing arguments, validating input, and generating help messages.

What are clipanion's main functionalities?

Command Definition

Clipanion allows you to define commands as classes, which can then be registered with a CLI instance. Each command can have its own execute method that contains the logic to be run when the command is invoked.

class MyCommand extends Command {
  execute() {
    console.log('Command executed!');
  }
}

const cli = new Cli();
cli.register(MyCommand);
cli.runExit(process.argv.slice(2));

Argument Parsing

Clipanion provides a declarative way to define command arguments using class properties. These arguments are automatically parsed and made available within the command's execute method.

class MyCommand extends Command {
  myArgument = Option.String();

  execute() {
    console.log(`Argument value: ${this.myArgument}`);
  }
}

const cli = new Cli();
cli.register(MyCommand);
cli.runExit(process.argv.slice(2));

Input Validation

Clipanion includes built-in validation for command arguments. You can specify whether an argument is required, and Clipanion will automatically enforce this when the command is run.

class MyCommand extends Command {
  myArgument = Option.String({ required: true });

  execute() {
    console.log(`Argument value: ${this.myArgument}`);
  }
}

const cli = new Cli();
cli.register(MyCommand);
cli.runExit(process.argv.slice(2));

Help Generation

Clipanion can automatically generate help messages for your commands. You can provide descriptions, detailed information, and usage examples that will be displayed when the help command is invoked.

class MyCommand extends Command {
  static usage = Command.Usage({
    description: 'My command description',
    details: 'Detailed information about my command',
    examples: [['Example usage', 'my-cli my-command']]
  });

  execute() {
    console.log('Command executed!');
  }
}

const cli = new Cli();
cli.register(MyCommand);
cli.runExit(process.argv.slice(2));

Other packages similar to clipanion

commander

Commander is one of the most popular CLI frameworks for Node.js. It offers a simple and expressive API for creating command-line applications. Compared to clipanion, commander has a more imperative style and does not use classes to define commands.

yargs

Yargs is another widely-used library for building CLIs. It provides a fluent interface for defining options and commands. Yargs focuses on parsing command-line arguments and generating help text, similar to clipanion, but with a different API design.

inquirer

Inquirer.js is a library for creating interactive command-line user interfaces. It is often used in conjunction with other CLI libraries to gather user input through a series of questions. While it does not handle command definition or parsing like clipanion, it complements these features with its interactive prompts.

README

Clipanion

Type-safe CLI library with no dependencies

Installation

yarn add clipanion

Why

• Clipanion supports advanced typing mechanisms
• Clipanion supports nested commands (yarn workspaces list)
• Clipanion supports transparent option proxying without -- (for example yarn dlx eslint --fix)
• Clipanion supports all option types you could think of (including negations, batches, ...)
• Clipanion offers a Yup integration for increased validation capabilities
• Clipanion generates an optimized state machine out of your commands
• Clipanion generates good-looking help pages out of the box
• Clipanion offers common optional command entries out-of-the-box (e.g. version command, help command)

Clipanion is used in Yarn with great success.

Recommended Usage

Note: This syntax assumes you have some way to compile decorators. TypeScript supports them via the experimentalDecorators setting, and Babel via the @babel/plugin-proposal-decorators plugin.

In essence you just need to declare a class that extends the Command abstract class, and implement the execute method. This function will then be called by Clipanion and its return value will be set as exit code by the engine (by default the exit code will be 0, which means success).

Options and command paths are set using the @Command decorators, unless you're in an environment that doesn't support them (in which case check the next section to see how to use the fallback syntax). Because you're in a regular class, you can even set default values to your options as you would with any other property!

import {Cli, Command} from 'clipanion';
import * as yup from 'yup';

// greet [-v,--verbose] [--name ARG]
class GreetCommand extends Command {
    @Command.Boolean(`-v,--verbose`)
    public verbose: boolean = false;

    @Command.String(`--name`)
    public name?: string;

    @Command.Path(`greet`)
    async execute() {
        if (typeof this.name === `undefined`) {
            this.context.stdout.write(`You're not registered.\n`);
        } else {
            this.context.stdout.write(`Hello, ${this.name}!\n`);
        }
    }
}

// fibo <a> <b>
class FibonacciCommand extends Command {
    @Command.String({required: true})
    public a!: number;

    @Command.String({required: true})
    public b!: number;

    @Command.Path(`fibo`)
    async execute() {
        // ...
    }

    static schema = yup.object().shape({
        a: yup.number().integer(),
        b: yup.number().integer(),
    })
}

const cli = new Cli({
    binaryLabel: `My Utility`,
    binaryName: `bin`,
    binaryVersion: `1.0.0`,
});

cli.register(GreetCommand);
cli.register(FibonacciCommand);

cli.runExit(process.argv.slice(2), {
    ...Cli.defaultContext,
});

Fallback Usage

In case the primary syntax isn't available (for example because you want to avoid any kind of transpilation), a fallback syntax is available:

class GreetCommand extends Command {
    async execute() {
        // ...
    }
}

GreetCommand.addPath(`greet`);

GreetCommand.addOption(`boolean`, Command.Boolean(`-v,--verbose`));
GreetCommand.addOption(`name`, Command.String(`--name`));

Note that in this case the option variables never get assigned default values, so they may be undefined within the execute block.

Decorators

The optionNames parameters all indicate that you should put there a comma-separated list of option names (along with their leading -). For example, -v,--verbose is a valid parameter.

@Command.Path(segment1?: string, segment2?: string, ...)

Specifies through which CLI path should trigger the command.

This decorator can only be set on the execute function itself, as it isn't linked to specific options.

class RunCommand extends Command {
    @Command.Path(segment1, segment2, segment3)
    async execute() {
        // ...
    }
}

Generates:

run segment1 segment2 segment3

Note that you can add as many paths as you want to a single command. By default it will be connected on the main entry point (empty path), but if you add even one explicit path this behavior will be disabled. If you still want the command to be available on both a named path and as a default entry point (for example yarn which is an alias for yarn install), simply call the decorator without segments:

class YarnCommand extends Command {
    @Command.Path(`install`)
    @Command.Path()
    async execute() {
        // ...
    }
}

Generates:

yarn install
# or
yarn

@Command.String(opts: {...})

Option	type	Description
required	boolean	Whether the positional argument is required or not

Specifies that the command accepts a positional argument. By default it will be required, but this can be toggled off using required.

class RunCommand extends Command {
    @Command.String()
    public foo?: string;
}

Generates:

run <ARG>
# => foo = ARG

Note that Clipanion supports required positional arguments both at the beginning and the end of the positional argument list (which allows you to build CLI for things like cp).

class RunCommand extends Command {
    @Command.String({required: false})
    public foo?: string;

    @Command.String()
    public bar!: string;
}

Generates:

run value1 value2
# => foo = value1
# => bar = value2

run value
# => foo = undefined
# => bar = value

run
# invalid

@Command.String(optionNames: string, opts: {...})

Option	type	Description
arity	number	Number of arguments for the option
description	string	Short description for the help message
hidden	boolean	Hide the option from any usage list
tolerateBoolean	boolean	Accept the option even if no argument is provided

Specifies that the command accepts an option that takes arguments (by default one, unless overriden via arity). Arguments can be specified on the command line using either --foo=ARG or --foo ARG.

class RunCommand extends Command {
    @Command.String(`-a,--arg`)
    arg?: string;
}

Generates:

run --arg <ARG>
run --arg=<ARG>
run -a <ARG>
run -a=<ARG>
# => arg = ARG

Be careful, by default, options that accept an argument must receive one on the CLI (ie --foo --bar wouldn't be valid if --foo accepts an argument).

This behaviour can be toggled off if the tolerateBoolean option is set. In this case, the option will act like a boolean flag if it doesn't have a value. Note that with this option on, arguments values can only be specified using the --foo=ARG syntax, which makes this option incompatible with arities higher than one.

class RunCommand extends Command {
    @Command.String(`--inspect`, {tolerateBoolean: true})
    public debug: boolean | string = false;
}

Generates:

run --inspect
# => debug = true

run --inspect=1234
# => debug = "1234"

run --inspect 1234
# invalid

@Command.Boolean(optionNames: string, opts: {...})

Option	type	Description
description	string	Short description for the help message
hidden	boolean	Hide the option from any usage list

Specifies that the command accepts a boolean flag as an option.

class RunCommand extends Command {
    @Command.Boolean(`--flag`)
    public flag: boolean;
}

Generates:

run --flag
# => flag = true

@Command.Counter(optionNames: string, {...})

Option	type	Description
description	string	Short description for the help message
hidden	boolean	Hide the option from any usage list

Specifies that the command accepts a boolean flag as an option, which will increment a counter for each detected occurrence. Each time the argument is negated, the counter will be reset to 0. The counter won't be set unless the option is found, so you must remember to set it to an appropriate default value.

class RunCommand extends Command {
    @Command.Counter('-v,--verbose')
    public verbose: number = 0;
}

Generates:

run
# => verbose = 0

run -v
# => verbose = 1

run -vv
# => verbose = 2

run --verbose -v --verbose -v
# => verbose = 4

run --verbose -v --verbose -v --no-verbose
# => verbose = 0

@Command.Array(optionNames: string, opts: {...})

Option	type	Description
arity	number	Number of arguments for the option
description	string	Short description for the help message
hidden	boolean	Hide the option from any usage list

Specifies that the command accepts a set of string arguments. The arity parameter defines how many values need to be accepted for each item.

class RunCommand extends Command {
    @Command.Array('--arg')
    public args: string[];

    @Command.Array('--point', {arity: 3})
    public points: [string, string, string][];
}

Generates:

run --arg value1 --arg value2
# => args = [value1, value2]

run --point x y z --point a b c
# => points = [['x', 'y', 'z'], ['a', 'b', 'c']]

@Command.Rest(opts: {...})

Option	type	Description
required	number	Number of required trailing arguments

Specifies that the command accepts an unlimited number of positional arguments. By default no arguments are required, but this can be changed by setting the required option.

class RunCommand extends Command {
    @Command.Rest()
    public values: string[];
    // ...
}

Generates:

run value1 value2
# => values = [value1, value2]

run value1
# => values = [value1]

run
# => values = []

Note: Rest arguments are strictly positionals. All options found between rest arguments will be consumed as options of the Command instance. If you wish to forward a list of option to another command without having to parse them yourself, use Command.Proxy instead.

Note: Rest arguments can be surrounded by other finite non-optional positionals such as Command.String({required: true}). Having multiple rest arguments in the same command is however invalid.

Advanced Example:

class CopyCommand extends Command {
    @Command.Rest({required: 1})
    sources: string[] = [];

    @Command.String()
    destination!: string;

    @Command.Boolean(`-f,--force`)
    force: boolean = false;

    @Command.String(`--reflink`, {tolerateBoolean: true})
    reflink: string | boolean = false;

    // ...
}

Generates:

run src dest
# => sources = [src]; destination = dest

run src1 src2 dest
# => sources = [src1, src2]; destination = dest

run src1 --force src2 dest
# => sources = [src1, src2]; destination = dest; force = true

run src1 src2 --reflink=always dest
# => sources = [src1, src2]; destination = dest; reflink = always

run src
# => Error - Not enough positional arguments.

run dest
# => Error - Not enough positional arguments.

@Command.Proxy(opts: {...})

Option	type	Description
required	number	Number of required trailing arguments

Specifies that the command accepts an infinite set of positional arguments that will not be consumed by the options of the Command instance. Use this decorator instead of Command.Rest when you wish to forward arguments to another command parsing them in any way. By default no arguments are required, but this can be changed by setting the required option.

class RunCommand extends Command {
    @Command.Proxy()
    public args: string[];
    // ...
}

Generates:

run value1 value2
# => values = [value1, value2]

run value1 --foo
# => values = [value1, --foo]

run --bar=baz
# => values = [--bar=baz]

Note: Proxying can only happen once per command. Once triggered, a command can't get out of "proxy mode", all remaining arguments being proxied into a list. "Proxy mode" can be triggered in the following ways:

• By passing a positional or an option that doesn't have any listeners attached to it. This happens when the listeners don't exist in the first place.

• By passing a positional that doesn't have any remaining listeners attached to it. This happens when the listeners have already consumed a positional.

• By passing the -- separator before an option that has a listener attached to it. This will cause Clipanion to activate "proxy mode" for all arguments after the separator, without proxying the separator itself. In all other cases, the separator will be proxied and not consumed by Clipanion.

Command Help Pages

Clipanion automatically adds support for the -h option to all the commands that you define. The information printed will come from the usage property attached to the class. For example, the following command:

class YarnAdd extends Command {
    static usage = Command.Usage({
        description: `remove dependencies from the project`,
        details: `
            This command will remove the specified packages from the current workspace. If the \`-A,--all\` option is set, the operation will be applied to all workspaces from the current project.
        `,
        examples: [[
            `Remove a dependency from the current project`,
            `$0 remove lodash`,
        ], [
            `Remove a dependency from all workspaces at once`,
            `$0 remove lodash --all`,
        ]],
    });
}

Will generate something like this:

Note that the inline code blocks will be automatically highlighted.

Optional Built-in Command Entries

Clipanion offers common optional command entries out-of-the-box, under the Command.Entries namespace.

They have to be manually registered:

cli.register(Command.Entries.Help);
cli.register(Command.Entries.Version);

Help Command - General Help Page

Paths: -h, --help

The Command.Entries.Help command displays the list of commands available to the application, printing a block similar to the following.

Version Command

Paths: -v, --version

The Command.Entries.Version command displays the version of the binary provided under binaryVersion when creating the CLI.

Composition

Commands can call each other by making use of their cli internal property:

class FooCommand extends Command {
    @Command.Path(`foo`)
    async execute() {
        this.context.stdout.write(`Hello World\n`);
    }
}

class BarCommand extends Command {
    @Command.Path(`bar`)
    async execute() {
        this.cli.run([`foo`]);
    }
}

Inheritance

Commands can extend each other and inherit options from each other:

abstract class BaseCommand extends Command {
    @Command.String(`--cwd`, {hidden: true})
    cwd?: string;

    abstract execute(): Promise<number | void>;
}

class FooCommand extends BaseCommand {
    @Command.String('--foo,-f')
    public foo?: string;

    async execute() {
        this.context.stdout.write(`Hello from ${this.cwd ?? process.cwd()}!\n`);
        this.context.stdout.write(`This is foo: ${this.foo}.\n`);
    }
}

Note: Because of the decorator evaluation order, positional arguments of a subclass will be consumed before positional arguments of a superclass. Because of this, it is not recommended to inherit anything other than options and handlers.

Lazy evaluation

Many commands have the following form:

import {uniqBy} from 'lodash';

export class MyCommand extends Command {
    async execute() {
        // ...
    }
}

While it works just fine, if you have a lot of command, each with its own set of dependencies (here, lodash), the startup time may suffer. This is because the import statements will always be eagerly evaluated, even if the command doesn't end up being used in the end. To solve this problem, you can move your imports inside the body of the execute function, thus making sure they'll only be evaluated if actually relevant:

export class MyCommand extends Command {
    async execute() {
        const {uniqBy} = await import(`lodash`);

        // ...
    }
}

This strategy is slightly harder to read, so it may not be necessary in every situation. If you like living on the edge, the babel-plugin-lazy-import plugin is meant to automatically apply this kind of transformation - although it requires you to run Babel on your sources.

Contexts

Commands share what is called a context. Contexts are a set of values defined when calling the run function from the CLI instance that will be made available to the commands via this.context. The default context contains properties for stdin, stdout, and stderr, but you can easily define a custom context that extends the default one:

import {BaseContext, Command} from 'clipanion';

type MyContext = BaseContext & {
    cwd: string;
};

class PwdCommand extends Command<MyContext> {
    async execute() {
        this.context.stdout.write(`${this.context.cwd}\n`);
    }
}

const cli = Cli.from<MyContext>([
    PwdCommands,
]);

cli.runExit(process.argv.slice(2), {
    ...Cli.defaultContext,
    cwd: process.cwd(),
});

Note that the context must be fully defined when calling run and runExit on the main CLI instance, but can be omitted or only partially specified when using this.cli.run (in which case only the specified fields will be changed).

License (MIT)

Copyright © 2019 Mael Nison

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.