bun run

The bun CLI can be used to execute JavaScript/TypeScript files, package.json scripts, and executable packages.

Performance

Bun is designed to start fast and run fast.

Under the hood Bun uses the JavaScriptCore engine, which is developed by Apple for Safari. In most cases, the startup and running performance is faster than V8, the engine used by Node.js and Chromium-based browsers. Its transpiler and runtime are written in Zig, a modern, high-performance language. On Linux, this translates into startup times 4x faster than Node.js.

Run a file

Use bun run to execute a source file.

bun run index.js

Bun supports TypeScript and JSX out of the box. Every file is transpiled on the fly by Bun's fast native transpiler before being executed.

bun run index.js

bun run index.jsx

bun run index.ts

bun run index.tsx

Alternatively, you can omit the run keyword and use the "naked" command; it behaves identically.

bun index.tsx

bun index.js

--watch

To run a file in watch mode, use the --watch flag.

bun --watch run index.tsx

bun --watch run dev # ✔️ do this

bun run dev --watch # ❌ don't do this

--smol

In memory-constrained environments, use the --smol flag to reduce memory usage at a cost to performance.

bun --smol run index.tsx

Run a package.json script

bun [bun flags] run <script> [script flags]

Your package.json can define a number of named "scripts" that correspond to shell commands.

{
  // ... other fields
  "scripts": {
    "clean": "rm -rf dist && echo 'Done.'",
    "dev": "bun server.ts"
  }
}

Use bun run <script> to execute these scripts.

bun run 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.

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.

bun run dev

To see a list of available scripts, run bun run without any arguments.

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.

--bun

It's common for package.json scripts to reference locally-installed CLIs like vite or next. These CLIs are often JavaScript files marked with a shebang to indicate that they should be executed with node.

#!/usr/bin/env node

// do stuff

By default, Bun respects this shebang and executes the script with node. However, you can override this behavior with the --bun flag. For Node.js-based CLIs, this will run the CLI with Bun instead of Node.js.

bun run --bun vite