Kieran Hunt

If you use mise-en-place to manage your dev tools (and you should), then you’ll probably find this trick really handy. You can quite easily use mise and Bun in the shebang line for a TypeScript file, and then have it: version manage the runtime, in-memory transpile the TypeScript to JavaScript, and run the script. It’ll do it all in one go:

#!/usr/bin/env -S mise x bun@1.4.2 -- bun

const greet = (name: string): void => console.log(`hi ${name}`);

greet('kieran');

// hi kieran

Pretty cool. I’m already using this trick in my Raycast script commands.

The first time you run this script, if you don’t already have the tool installed, mise will helpfully install it for you. Mine installs into ~/.local/share/mise/installs/<tool>/<version>/. Bun went to ~/.local/share/mise/installs/bun/1.4.2/bin/bun.

You can also run it without a version number:

#!/usr/bin/env -S mise x bun -- bun

And then mise will source the version number from your local mise.toml file. This approach has some caveats though: you have to have a separate mise.toml file and you have to execute the script from the same directory as that file.

Bun has another trick up its sleeve. It’ll auto-install dependencies when it finds no package.json:

#!/usr/bin/env -S mise x bun@1.4.2 -- bun

import { z } from "zod";

const Pet = z.object({ name: z.string(), legs: z.number().int().min(0) });

const good: unknown = { name: "mochi", legs: 4 };
const bad: unknown = { name: "mochi", legs: -2 };

console.log(Pet.parse(good));
console.log(Pet.safeParse(bad).error?.issues[0].message);

And you can even specify a version number for the zod import. Like this: import { z } from "zod@^4";. However it seems like bun has a bug at the moment whereby it fails if its package cache directory already contains a different version of the same dependency.