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The `bun` CLI can be used to execute JavaScript/TypeScript files, `package.json` scripts, and [executable packages](https://docs.npmjs.com/cli/v9/configuring-npm/package-json#bin).
## Running a file
{% callout %}
Compare to `node <file>`
{% /callout %}
Bun can execute `.js`, `.jsx`, `.ts`, and `.tsx` files. Every file is transpiled to vanilla JavaScript by Bun's fast native transpiler before being executed. For details on Bun's runtime, refer to the [Bun runtime](/docs/runtime) documentation.
```ts#foo.ts
import { z } from "zod";
const schema = z.string()
const result = schema.parse("Billie Eilish");
console.log(result);
```
To run a file in Bun:
```bash
$ bun foo.ts
Billie Eilish
```
If no `node_modules` directory is found in the working directory or above, Bun will abandon Node.js-style module resolution in favor of the `Bun module resolution algorithm`. Under Bun-style module resolution, all packages are _auto-installed_ on the fly into a [global module cache](/docs/cli/install#global-cache). For full details on this algorithm, refer to [Runtime > Modules](/docs/runtime/modules).
## Running a package script
{% note %}
Compare to `npm run <script>` or `yarn <script>`
{% /note %}
Your `package.json` can define a number of named `"scripts"` that correspond to shell commands.
```jsonc
{
// ... other fields
"scripts": {
"clean": "rm -rf dist && echo 'Done.'",
"dev": "bun server.ts"
}
}
```
Use `bun <script>` to execute these scripts.
```bash
$ bun clean
$ rm -rf dist && echo 'Done.'
Cleaning...
Done.
```
Bun executes the script command in a subshell. It checks for the following shells in order, using the first one it finds: `bash`, `sh`, `zsh`.
{% callout %}
⚡️ The startup time for `npm run` on Linux is roughly 170ms; with Bun it is `6ms`.
{% /callout %}
If there is a name conflict between a `package.json` script and a built-in `bun` command (`install`, `dev`, `upgrade`, etc.) Bun's built-in command takes precedence. In this case, use the more explicit `bun run` command to execute your package script.
```bash
$ bun run dev
```
To see a list of available scripts, run `bun run` without any arguments.
```bash
$ bun run
quickstart scripts:
bun run clean
rm -rf dist && echo 'Done.'
bun run dev
bun server.ts
2 scripts
```
Bun respects lifecycle hooks. For instance, `bun run clean` will execute `preclean` and `postclean`, if defined. If the `pre<script>` fails, Bun will not execute the script itself.
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