https://github.com/Xunnamius/black-flag
🏴 A declarative yargs-based framework for building fluent command line interfaces that are easy to maintain and extend
https://github.com/Xunnamius/black-flag
arguments cli command interface line option optstring parameters parse user yargs
Last synced: 3 months ago
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🏴 A declarative yargs-based framework for building fluent command line interfaces that are easy to maintain and extend
- Host: GitHub
- URL: https://github.com/Xunnamius/black-flag
- Owner: Xunnamius
- License: mit
- Created: 2023-10-21T13:03:57.000Z (almost 2 years ago)
- Default Branch: main
- Last Pushed: 2025-07-10T10:20:00.000Z (3 months ago)
- Last Synced: 2025-07-10T15:15:54.289Z (3 months ago)
- Topics: arguments, cli, command, interface, line, option, optstring, parameters, parse, user, yargs
- Language: TypeScript
- Homepage: https://npm.im/@black-flag/core
- Size: 6.45 MB
- Stars: 4
- Watchers: 1
- Forks: 0
- Open Issues: 5
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- Funding: .github/FUNDING.yml
- License: LICENSE
- Code of conduct: .github/CODE_OF_CONDUCT.md
- Codeowners: .github/CODEOWNERS
- Security: SECURITY.md
- Support: .github/SUPPORT.md
Awesome Lists containing this project
README
A declarative wrapper around Yargs for building beautiful, fluent command line interfaces
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# Black Flag 🏴
Black Flag is a fairly thin library that wraps [yargs][1], extending its
capabilities with several powerful **declarative** features. It can be used to
create simple single-level CLIs or deeply nested sprawling interfaces alike.
Black Flag was built as a drop-in replacement for vanilla Yargs, specifically
for users of the [`yargs::commandDir()`][2] ([which][3] [has][4] [its][5]
[issues][6]). Its features include:
- [Declarative-first sync/async APIs][7] ✨
- [Zero configuration required][8] ✨
- [It's still yargs all the way down][9] ✨ (nothing brand new to learn!)
- [Built-in support for dynamic options][10] ✨ ([an][11] [infamous][12]
[Yargs][13] [white][14] [whale][15])
- [Consistent and safe CLI execution][16] ✨
- [Simple comprehensive error handling][17] ✨
- [A pleasant testing experience][18] ✨
- [Builtin TypeScript intellisense][19] ✨
Black Flag is tested on Ubuntu and Windows 10, and like Yargs tracks Node.js LTS
versions. Also comes with first-class support for both CJS and ESM source.
❖ [Quick start][20]\
❖ [Step-by-step getting started guide][21]\
❖ [Black Flag versus vanilla Yargs][22]\
❖ [Simple demo CLI project][23] (or `npx -p @black-flag/demo myctl --help`)\
❖ [Black Flag recipes for solving common CLI design problems][24]\
❖ [Black Flag's intro examples][25] (which are just [Yargs's intro examples][26] rewritten with Black Flag)
❖ [Builder API][27] (essentially `yargs::options`'s `opt` keys)\
❖ [Command module API][28]\
❖ [Configuration hooks API][29]\
❖ [BFE extended `builder` API][30]\
❖ [All `@black-flag/core` exports][31]\
❖ [All `@black-flag/core/util` exports][32]\
❖ [All `@black-flag/extensions` exports][33]\
❖ [All `@black-flag/checks` exports][34]
> [!TIP]
>
> If you find yourself a fan of Black Flag's more declarative DX and want to go
> all the way, check out [Black Flag Extensions][35] (BFE). BFE is a collection
> of surprisingly simple set-theoretic APIs that build on
> [`yargs::options()`][27] for a **fully declarative developer experience**. BFE
> also protects you from [a couple Yargs footguns][36] that Black Flag by itself
> cannot.
>
> You may also be interested in [Black Flag Checks][37] (BFC), which offers
> several pluggable [`yargs::check`][38] functions—like `checkIsNotNegative` and
> `checkArrayNotEmpty`—built to work with BFE.
---
- [Install](#install)
- [Quick Start](#quick-start)
- [Appendix 🏴](#appendix-)
- [Terminology](#terminology)
- [Inspiration](#inspiration)
- [Published Package Details](#published-package-details)
- [License](#license)
- [Contributing and Support](#contributing-and-support)
- [Contributors](#contributors)
## Install
To install:
```shell
npm install @black-flag/core
```
And if you're ready to go all in on Black Flag's declarative API, check out
[Black Flag Extensions][35]:
```shell
npm install @black-flag/extensions
```
## Quick Start
Install Black Flag:
```shell
npm install @black-flag/core
```
Create the file that will run your CLI, perhaps at `./cli.js`:
> [!TIP]
>
> Both CJS and ESM source is acceptable!
```js
#!/usr/bin/env node
import { runProgram } from '@black-flag/core';
export default runProgram(import.meta.resolve('./commands'));
```
Then create the root command, perhaps at `./commands/index.js`:
```js
export const name = 'pirate-parser';
export const usage = 'Usage: $0 [args]';
```
Finally, create a subcommand, perhaps at `./commands/hello.js`:
```js
export const command = '$0 [name]';
export const description =
'Welcome ter black flag, a declarative wrapper around yargs!';
export function builder(blackFlag, helpOrVersionSet, argv) {
blackFlag.positional('name', {
type: 'string',
default: 'Cambi',
describe: 'The name to say hello to'
});
// A special --attention flag only available when greeting the captain!
if (helpOrVersionSet || argv?.name === 'CAPTAIN') {
return {
attention: {
boolean: true,
description: `Alert the watch${
helpOrVersionSet ? ' (only available when greeting captain)' : ''
}`
}
};
}
}
export async function handler(argv) {
if (argv.attention) {
console.log('-!- Captain is on the bridge -!-');
}
console.log(`Hello ${argv.name}, welcome to Black Flag!`);
}
```
> [!TIP]
>
> This example demonstrates a multi-level or "nested" command, i.e. a _root
> command_ with a _subcommand_. If instead we wanted to make a simple
> single-level CLI with no subcommands at all, we could merge
> `./commands/hello.js`'s exports (`handler`, `builder`, etc) into
> `./commands/index.js`.
>
> How you design your CLI is up to you!
Then run it:
```shell
node cli.js --help
```
```text
Usage: pirate-parser [args]
Commands:
pirate-parser hello Welcome ter black flag, a declarative wrapper around yargs!
Options:
--help Show help text [boolean]
--version Show version number [boolean]
```
---
```shell
node cli.js hello --help
```
```text
Usage: pirate-parser hello [name]
Welcome ter black flag, a declarative wrapper around yargs!
Positionals:
name The name to say hello to [string] [default: "Cambi"]
Options:
--help Show help text [boolean]
--attention Alert the watch (only available when greeting captain) [boolean]
```
---
```shell
node cli.js hello Parrot
```
```text
Hello Parrot, welcome to Black Flag!
```
---
```shell
node cli.js hello CAPTAIN
```
```text
Hello CAPTAIN, welcome to Black Flag!
```
---
```shell
node cli.js hello Parrot --attention
```
```text
Usage: pirate-parser hello [name]
Positionals:
name The name to say hello to [string] [default: "Cambi"]
Options:
--help Show help text [boolean]
Unknown argument: attention
```
---
```shell
node cli.js hello CAPTAIN --attention
```
```text
-!- Captain is on the bridge -!-
Hello CAPTAIN, welcome to Black Flag!
```
> [!TIP]
>
> Not sure what makes Black Flag "more declarative" than Yargs? Compare this
> quick start example to the
> vanilla Yargs version.
Next steps:
- [Check out the step-by-step getting started guide][21]
- [Compare Black Flag versus vanilla Yargs][22]
- [Play with a simple demo CLI project][23] (or
`npx -p @black-flag/demo myctl --help`)
- [Review Black Flag recipes for solving common CLI design problems][24]
- [Deep dive into Black Flag's internals][39]
- [Pull up Black Flag's introductory examples][25] (or [Yargs's][26])
- [Pore over Yargs's parser tricks][40] (which also apply to Black Flag)
## Appendix 🏴
Further documentation can be found under [`docs/`][x-repo-docs] and
[`docs/api/`][41]. Common CLI design "recipes" can be found under
[`examples/`][24].
### Terminology
| Term | Description |
| :-------------: | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| command | A "command" is a functional unit associated with a [configuration][28] file and represented internally as a trio of programs: [effector, helper, and router][39]. Further, each command is classified as one of: "pure parent" (root and parent), "parent-child" (parent and child), or "pure child" (child). |
| program | A "program" is a Yargs instance wrapped in a [`Proxy`][42] granting the instance an expanded set of features. Programs are represented internally by the [`Program`][43] type. |
| root | The tippy top command in your hierarchy of commands and the entry point for any Black Flag application. Also referred to as the "root command". |
| default command | A "default command" is [Yargs parlance][44] for the CLI entry point. Technically there is no concept of a "default command" at the Black Flag level, though there is the _root command_. |
### Inspiration
Expand details
I love Yargs 💕 Yargs is the greatest! I've made dozens of CLI tools with Yargs,
each with drastically different interfaces and requirements. Some help manage
critical systems.
As I was copying-and-pasting some configs from past projects for yet another
tool, I realized the (irritatingly disparate 😖) structures of my CLI projects
up until this point were converging on a set of personal conventions around
Yargs. And, as I'm [always eager][45] to ["optimize" my workflows][46], I
wondered how much common functionality could be abstracted away.
The goal: make my CLIs more stable upon release, much faster to build, and more
pleasant to test. And also avoid Yargs's most egregious footguns. But perhaps
most important: I wanted CLIs that would remain simple and consistent to
maintain.
Throw in a re-watch of the PotC series and Black Flag was born! 🏴☠🍾
### Published Package Details
This is a [CJS2 package][x-pkg-cjs-mojito] with statically-analyzable exports
built by Babel for use in Node.js versions that are not end-of-life. For
TypeScript users, this package supports both `"Node10"` and `"Node16"` module
resolution strategies.
Expand details
That means both CJS2 (via `require(...)`) and ESM (via `import { ... } from ...`
or `await import(...)`) source will load this package from the same entry points
when using Node. This has several benefits, the foremost being: less code
shipped/smaller package size, avoiding [dual package
hazard][x-pkg-dual-package-hazard] entirely, distributables are not
packed/bundled/uglified, a drastically less complex build process, and CJS
consumers aren't shafted.
Each entry point (i.e. `ENTRY`) in [`package.json`'s
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### License
See [LICENSE][x-repo-license].
## Contributing and Support
**[New issues][x-repo-choose-new-issue] and [pull requests][x-repo-pr-compare]
are always welcome and greatly appreciated! 🤩** Just as well, you can [star 🌟
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more information.
### Contributors
[](#contributors-)
Thanks goes to these wonderful people ([emoji
key][x-repo-all-contributors-emojis]):
Bernard
🚇 💻 📖 🚧 ⚠️ 👀
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[1]: https://yargs.js.org
[2]: https://yargs.js.org/docs#api-reference-commanddirdirectory-opts
[3]: https://github.com/yargs/yargs/issues/1306
[4]: https://github.com/yargs/yargs/issues/1269
[5]: https://github.com/yargs/yargs/issues/1975
[6]: https://github.com/yargs/yargs/issues/2152
[7]: ./docs/features.md#declaratively-build-deep-command-hierarchies-
[8]: ./docs/features.md#convention-over-configuration-
[9]: ./docs/features.md#its-yargs-all-the-way-down-
[10]: ./docs/features.md#built-in-support-for-dynamic-options-
[11]: https://github.com/yargs/yargs/issues/793
[12]: https://github.com/yargs/yargs/issues/2119
[13]: https://github.com/yargs/yargs/issues/2256
[14]: https://github.com/yargs/yargs/issues/2227
[15]: https://github.com/yargs/yargs/issues/2133
[16]: ./docs/features.md#run-your-tool-safely-and-consistently-
[17]: ./docs/features.md#simple-comprehensive-error-handling-and-reporting-
[18]: ./docs/features.md#a-pleasant-testing-experience-
[19]: ./docs/features.md#extensive-intellisense-support-
[20]: #quick-start
[21]: ./docs/getting-started.md
[22]: ./docs/bf-vs-yargs.md
[23]: https://github.com/Xunnamius/black-flag-demo
[24]: ./examples/README.md
[25]: ./examples/yargs-intro/README.md
[26]: https://github.com/yargs/yargs/blob/HEAD/docs/examples.md
[27]: https://yargs.js.org/docs#api-reference-optionskey-opt
[28]: ./docs/api/src/exports/type-aliases/Configuration.md
[29]: ./docs/api/src/exports/type-aliases/ConfigurationHooks.md
[30]:
./packages/extensions/docs/index/type-aliases/BfeBuilderObjectValueExtensions.md
[31]: ./docs/api/src/exports/README.md
[32]: ./docs/api/src/exports/util/README.md
[33]: ./packages/extensions/docs/index/README.md
[34]: ./packages/checks/docs/index/README.md
[35]: ./packages/extensions/README.md
[36]: ./docs/bf-vs-yargs.md#irrelevant-differences
[37]: ./packages/checks/README.md
[38]: https://yargs.js.org/docs#api-reference-checkfn-globaltrue
[39]: ./docs/advanced.md
[40]: https://github.com/yargs/yargs/blob/main/docs/tricks.md
[41]: ./docs/api/README.md
[42]:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy
[43]: ./docs/api/src/exports/util/type-aliases/Program.md
[44]: https://github.com/yargs/yargs/blob/main/docs/advanced.md#default-commands
[45]: https://xkcd.com/1205
[46]: https://i.redd.it/0cm6yx27tez21.jpg