shadcn-ui/ui codebase analysis: How does shadcn-ui CLI work? — Part 1.0

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.

// 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

#!/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 discuss three commands; add , diff , init

These commands are imported from a folder named commands in src folder.

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

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. It is from the Legend, Sindre Sorhus. I see this guy’s name so often when I dig into open source.

fs.readJSONSync reads a JSON file and then parses it into an object. In this case, it is an object of type PackageJson.

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)

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.

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References:

1. 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
3. https://dev.to/superiqbal7/graceful-shutdown-in-nodejs-handling-stranger-danger-29jo