shadcn-ui/ui codebase analysis: How does shadcn-ui CLI work? — Part 1.0
Tags: javascript, nextjs, opensource, shadcnui
Published: 2024-06-24 20:44:31

I wanted to find out how shadcn-ui CLI works. In this article, I discuss the code used to build the shadcn-ui/ui CLI. In part 1, we will look at a code snippet picked from [packages/cli/src/index.ts](https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/index.ts).

```js
// source: https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/index.ts
#!/usr/bin/env node
import { add } from "@/src/commands/add"
import { diff } from "@/src/commands/diff"
import { init } from "@/src/commands/init"
import { Command } from "commander"

import { getPackageInfo } from "./utils/get-package-info"

process.on("SIGINT", () => process.exit(0))
process.on("SIGTERM", () => process.exit(0))

async function main() {
  const packageInfo = await getPackageInfo()

  const program = new Command()
    .name("shadcn-ui")
    .description("add components and dependencies to your project")
    .version(
      packageInfo.version || "1.0.0",
      "-v, --version",
      "display the version number"
    )

  program.addCommand(init).addCommand(add).addCommand(diff)

  program.parse()
}

main()
```

There’s about 29 lines of code in index.ts

Imports used
------------

```js
#!/usr/bin/env node
import { add } from "@/src/commands/add"
import { diff } from "@/src/commands/diff"
import { init } from "@/src/commands/init"
import { Command } from "commander"

import { getPackageInfo } from "./utils/get-package-info"
```

[Shadcn CLI docs](https://ui.shadcn.com/docs/cli) discuss three commands; add , diff , init

These commands are imported from a folder named [commands in src folder.](https://github.com/shadcn-ui/ui/tree/main/packages/cli/src)

[Commander](https://www.npmjs.com/package/commander) is an npm package used here to enable CLI interactions.

### getPackageInfo

getPackageInfo is a small utility function found in [utils/get-package-info.ts](https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/utils/get-package-info.ts#L5)

![](https://media.licdn.com/dms/image/D5612AQGKuMpgUQAOWg/article-inline_image-shrink_1500_2232/0/1719261554312?e=1724889600&v=beta&t=HcWkx30tuuWehhUq1RHkAHbTO0uD-mKAyVhQAbJKcX8)

```js
import path from "path"
import fs from "fs-extra"
import { type PackageJson } from "type-fest"

export function getPackageInfo() {
  const packageJsonPath = path.join("package.json")

  return fs.readJSONSync(packageJsonPath) as PackageJson
}
```

Notice how there’s an enforced PackageJson type from [type-fest](https://github.com/sindresorhus/type-fest). It is from the Legend, Sindre Sorhus. I see this guy’s name so often when I dig into open source.

[fs.readJSONSync](https://github.com/jprichardson/node-fs-extra/blob/d96f2655f181f1c6b1641711619400140a89d027/docs/readJson-sync.md) reads a JSON file and then parses it into an object. In this case, it is an object of type PackageJson.

```js
process.on("SIGINT", () => process.exit(0))
process.on("SIGTERM", () => process.exit(0))
```

**SIGINT:** This is a signal that is typically sent to a process when a user types Ctrl+C in the terminal. It is often used to request that a process terminate gracefully. When a process receives a SIGINT signal, it can catch it and perform any necessary cleanup operations before terminating.

**SIGTERM:** This is a signal that is typically sent to a process by the operating system to request that the process terminate. It is often used as a graceful way to ask a process to terminate, allowing it to perform any necessary cleanup operations before exiting. Processes can catch this signal and perform cleanup operations before terminating. ([Source](https://dev.to/superiqbal7/graceful-shutdown-in-nodejs-handling-stranger-danger-29jo))

Conclusion:
-----------

I have seen Commander.js being used in Next.js create-next-app package, I see it in use here again in shadcn-ui/ui. I will continue picking small code snippets from this CLI package and discuss the code. I liked the way package.json is read using a utility function getPackageInfo. This getPackageInfo uses fs.readJSONSync. There is Type assertion applied using PackageJson provided by type-fest on the Object returned by fs.readJSONSync.

> _Want to learn how to build shadcn-ui/ui from scratch? Check out_ [_build-from-scratch_](https://tthroo.com/)

About me:
---------

Website: [https://ramunarasinga.com/](https://ramunarasinga.com/)

Linkedin: [https://www.linkedin.com/in/ramu-narasinga-189361128/](https://www.linkedin.com/in/ramu-narasinga-189361128/)

Github: [https://github.com/Ramu-Narasinga](https://github.com/Ramu-Narasinga)

Email: [ramu.narasinga@gmail.com](mailto:ramu.narasinga@gmail.com)

References:
-----------

1.  [https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/index.ts](https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/index.ts)
2.  [https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/utils/get-package-info.ts#L5](https://github.com/shadcn-ui/ui/blob/main/packages/cli/src/utils/get-package-info.ts#L5)
3.  [https://dev.to/superiqbal7/graceful-shutdown-in-nodejs-handling-stranger-danger-29jo](https://dev.to/superiqbal7/graceful-shutdown-in-nodejs-handling-stranger-danger-29jo)