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Use `bunx` to auto-install and run packages from `npm`. The `bunx` CLI will be auto-installed when you install `bun`.
```bash
$ bunx cowsay "Hello world!"
```
{% callout %}
⚡️ **Speed** — With Bun's fast startup times, `bunx` is [roughly 100x faster](https://twitter.com/jarredsumner/status/1606163655527059458) than `npx` for locally installed packages.
{% /callout %}
Packages can declare executables in the `"bin"` field of their `package.json`. These are known as _package executables_ or _package binaries_.
```jsonc#package.json
{
// ... other fields
"name": "my-cli",
"bin": {
"my-cli": "dist/index.js"
}
}
```
These executables are commonly plain JavaScript files marked with a [shebang line](<https://en.wikipedia.org/wiki/Shebang_(Unix)>) to indicate which program should be used to execute them. The following file indicates that it should be executed with `node`.
```js#dist/index.js
#!/usr/bin/env node
console.log("Hello world!");
```
These executables can be run with `bunx`,
```bash
$ bunx my-cli
```
As with `npx`, `bunx` will check for a locally installed package first, then fall back to auto-installing the package from `npm`. Installed packages will be stored in Bun's global cache for future use.
## Arguments and flags
To pass additional command-line flags and arguments through to the executable, place them after the executable name.
```bash
$ bunx my-cli --foo bar
```
## Shebangs
By default, Bun respects shebangs. If an executable is marked with `#!/usr/bin/env node`, Bun will spin up a `node` process to execute the file. However, in some cases it may be desirable to run executables using [Bun's runtime](/docs/runtime), even if the executable indicates otherwise. To do so, include the `--bun` flag.
```bash
$ bunx --bun my-cli
```
{% callout %}
**Note** — The `--bun` flag must occur _before_ the executable name. Flags that appear _after_ the name are passed through to the executable.
```bash
$ bunx --bun my-cli # good
$ bunx my-cli --bun # bad
```
{% /callout %}
## Environment variables
Bun automatically loads environment variables from `.env` files before running a file, script, or executable. The following files are checked, in order:
1. `.env.local` (first)
2. `NODE_ENV` === `"production"` ? `.env.production` : `.env.development`
3. `.env`
To debug environment variables, run `bun run env` to view a list of resolved environment variables.
|
