bun-types
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Type definitions and documentation for Bun, an incredibly fast JavaScript runtime
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Bun Shell makes shell scripting with JavaScript & TypeScript fun. It's a cross-platform bash-like shell with seamless JavaScript interop.
Quickstart:
```js
import { $ } from "bun";
const response = await fetch("https://example.com");
// Use Response as stdin.
await $`cat < ${response} | wc -c`; // 1256
```
## Features:
- **Cross-platform**: works on Windows, Linux & macOS. Instead of `rimraf` or `cross-env`', you can use Bun Shell without installing extra dependencies. Common shell commands like `ls`, `cd`, `rm` are implemented natively.
- **Familiar**: Bun Shell is a bash-like shell, supporting redirection, pipes, environment variables and more.
- **Globs**: Glob patterns are supported natively, including `**`, `*`, `{expansion}`, and more.
- **Template literals**: Template literals are used to execute shell commands. This allows for easy interpolation of variables and expressions.
- **Safety**: Bun Shell escapes all strings by default, preventing shell injection attacks.
- **JavaScript interop**: Use `Response`, `ArrayBuffer`, `Blob`, `Bun.file(path)` and other JavaScript objects as stdin, stdout, and stderr.
- **Shell scripting**: Bun Shell can be used to run shell scripts (`.bun.sh` files).
- **Custom interpreter**: Bun Shell is written in Zig, along with it's lexer, parser, and interpreter. Bun Shell is a small programming language.
## Getting started
The simplest shell command is `echo`. To run it, use the `$` template literal tag:
```js
import { $ } from "bun";
await $`echo "Hello World!"`; // Hello World!
```
By default, shell commands print to stdout. To quiet the output, call `.quiet()`:
```js
import { $ } from "bun";
await $`echo "Hello World!"`.quiet(); // No output
```
What if you want to access the output of the command as text? Use `.text()`:
```js
import { $ } from "bun";
// .text() automatically calls .quiet() for you
const welcome = await $`echo "Hello World!"`.text();
console.log(welcome); // Hello World!\n
```
By default, `await`ing will return stdout and stderr as `Buffer`s.
```js
import { $ } from "bun";
const { stdout, stderr } = await $`echo "Hello World!"`.quiet();
console.log(stdout); // Buffer(6) [ 72, 101, 108, 108, 111, 32 ]
console.log(stderr); // Buffer(0) []
```
## Error handling
By default, non-zero exit codes will throw an error. This `ShellError` contains information about the command run.
```js
import { $ } from "bun";
try {
const output = await $`something-that-may-fail`.text();
console.log(output);
} catch (err) {
console.log(`Failed with code ${err.exitCode}`);
console.log(err.stdout.toString());
console.log(err.stderr.toString());
}
```
Throwing can be disabled with `.nothrow()`. The result's `exitCode` will need to be checked manually.
```js
import { $ } from "bun";
const { stdout, stderr, exitCode } = await $`something-that-may-fail`
.nothrow()
.quiet();
if (exitCode !== 0) {
console.log(`Non-zero exit code ${exitCode}`);
}
console.log(stdout);
console.log(stderr);
```
The default handling of non-zero exit codes can be configured by calling `.nothrow()` or `.throws(boolean)` on the `$` function itself.
```js
import { $ } from "bun";
// shell promises will not throw, meaning you will have to
// check for `exitCode` manually on every shell command.
$.nothrow(); // equivalent to $.throws(false)
// default behavior, non-zero exit codes will throw an error
$.throws(true);
// alias for $.nothrow()
$.throws(false);
await $`something-that-may-fail`; // No exception thrown
```
## Redirection
A command's _input_ or _output_ may be _redirected_ using the typical Bash operators:
- `<` redirect stdin
- `>` or `1>` redirect stdout
- `2>` redirect stderr
- `&>` redirect both stdout and stderr
- `>>` or `1>>` redirect stdout, _appending_ to the destination, instead of overwriting
- `2>>` redirect stderr, _appending_ to the destination, instead of overwriting
- `&>>` redirect both stdout and stderr, _appending_ to the destination, instead of overwriting
- `1>&2` redirect stdout to stderr (all writes to stdout will instead be in stderr)
- `2>&1` redirect stderr to stdout (all writes to stderr will instead be in stdout)
Bun Shell also supports redirecting from and to JavaScript objects.
### Example: Redirect output to JavaScript objects (`>`)
To redirect stdout to a JavaScript object, use the `>` operator:
```js
import { $ } from "bun";
const buffer = Buffer.alloc(100);
await $`echo "Hello World!" > ${buffer}`;
console.log(buffer.toString()); // Hello World!\n
```
The following JavaScript objects are supported for redirection to:
- `Buffer`, `Uint8Array`, `Uint16Array`, `Uint32Array`, `Int8Array`, `Int16Array`, `Int32Array`, `Float32Array`, `Float64Array`, `ArrayBuffer`, `SharedArrayBuffer` (writes to the underlying buffer)
- `Bun.file(path)`, `Bun.file(fd)` (writes to the file)
### Example: Redirect input from JavaScript objects (`<`)
To redirect the output from JavaScript objects to stdin, use the `<` operator:
```js
import { $ } from "bun";
const response = new Response("hello i am a response body");
const result = await $`cat < ${response}`.text();
console.log(result); // hello i am a response body
```
The following JavaScript objects are supported for redirection from:
- `Buffer`, `Uint8Array`, `Uint16Array`, `Uint32Array`, `Int8Array`, `Int16Array`, `Int32Array`, `Float32Array`, `Float64Array`, `ArrayBuffer`, `SharedArrayBuffer` (reads from the underlying buffer)
- `Bun.file(path)`, `Bun.file(fd)` (reads from the file)
- `Response` (reads from the body)
### Example: Redirect stdin -> file
```js
import { $ } from "bun";
await $`cat < myfile.txt`;
```
### Example: Redirect stdout -> file
```js
import { $ } from "bun";
await $`echo bun! > greeting.txt`;
```
### Example: Redirect stderr -> file
```js
import { $ } from "bun";
await $`bun run index.ts 2> errors.txt`;
```
### Example: Redirect stderr -> stdout
```js
import { $ } from "bun";
// redirects stderr to stdout, so all output
// will be available on stdout
await $`bun run ./index.ts 2>&1`;
```
### Example: Redirect stdout -> stderr
```js
import { $ } from "bun";
// redirects stdout to stderr, so all output
// will be available on stderr
await $`bun run ./index.ts 1>&2`;
```
## Piping (`|`)
Like in bash, you can pipe the output of one command to another:
```js
import { $ } from "bun";
const result = await $`echo "Hello World!" | wc -w`.text();
console.log(result); // 2\n
```
You can also pipe with JavaScript objects:
```js
import { $ } from "bun";
const response = new Response("hello i am a response body");
const result = await $`cat < ${response} | wc -w`.text();
console.log(result); // 6\n
```
## Command substitution (`$(...)`)
Command substitution allows you to substitute the output of another script into the current script:
```js
import { $ } from "bun";
// Prints out the hash of the current commit
await $`echo Hash of current commit: $(git rev-parse HEAD)`;
```
This is a textual insertion of the command's output and can be used to, for example, declare a shell variable:
```js
import { $ } from "bun";
await $`
REV=$(git rev-parse HEAD)
docker built -t myapp:$REV
echo Done building docker image "myapp:$REV"
`;
```
{% callout %}
**NOTE**: Because Bun internally uses the special [`raw`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals#raw_strings) property on the input template literal, using the backtick syntax for command substitution won't work:
```js
import { $ } from "bun";
await $`echo \`echo hi\``;
```
Instead of printing:
```
hi
```
The above will print out:
```
echo hi
```
We instead recommend sticking to the `$(...)` syntax.
{% /callout %}
## Environment variables
Environment variables can be set like in bash:
```js
import { $ } from "bun";
await $`FOO=foo bun -e 'console.log(process.env.FOO)'`; // foo\n
```
You can use string interpolation to set environment variables:
```js
import { $ } from "bun";
const foo = "bar123";
await $`FOO=${foo + "456"} bun -e 'console.log(process.env.FOO)'`; // bar123456\n
```
Input is escaped by default, preventing shell injection attacks:
```js
import { $ } from "bun";
const foo = "bar123; rm -rf /tmp";
await $`FOO=${foo} bun -e 'console.log(process.env.FOO)'`; // bar123; rm -rf /tmp\n
```
### Changing the environment variables
By default, `process.env` is used as the environment variables for all commands.
You can change the environment variables for a single command by calling `.env()`:
```js
import { $ } from "bun";
await $`echo $FOO`.env({ ...process.env, FOO: "bar" }); // bar
```
You can change the default environment variables for all commands by calling `$.env`:
```js
import { $ } from "bun";
$.env({ FOO: "bar" });
// the globally-set $FOO
await $`echo $FOO`; // bar
// the locally-set $FOO
await $`echo $FOO`.env({ FOO: "baz" }); // baz
```
You can reset the environment variables to the default by calling `$.env()` with no arguments:
```js
import { $ } from "bun";
$.env({ FOO: "bar" });
// the globally-set $FOO
await $`echo $FOO`; // bar
// the locally-set $FOO
await $`echo $FOO`.env(undefined); // ""
```
### Changing the working directory
You can change the working directory of a command by passing a string to `.cwd()`:
```js
import { $ } from "bun";
await $`pwd`.cwd("/tmp"); // /tmp
```
You can change the default working directory for all commands by calling `$.cwd`:
```js
import { $ } from "bun";
$.cwd("/tmp");
// the globally-set working directory
await $`pwd`; // /tmp
// the locally-set working directory
await $`pwd`.cwd("/"); // /
```
## Reading output
To read the output of a command as a string, use `.text()`:
```js
import { $ } from "bun";
const result = await $`echo "Hello World!"`.text();
console.log(result); // Hello World!\n
```
### Reading output as JSON
To read the output of a command as JSON, use `.json()`:
```js
import { $ } from "bun";
const result = await $`echo '{"foo": "bar"}'`.json();
console.log(result); // { foo: "bar" }
```
### Reading output line-by-line
To read the output of a command line-by-line, use `.lines()`:
```js
import { $ } from "bun";
for await (let line of $`echo "Hello World!"`.lines()) {
console.log(line); // Hello World!
}
```
You can also use `.lines()` on a completed command:
```js
import { $ } from "bun";
const search = "bun";
for await (let line of $`cat list.txt | grep ${search}`.lines()) {
console.log(line);
}
```
### Reading output as a Blob
To read the output of a command as a Blob, use `.blob()`:
```js
import { $ } from "bun";
const result = await $`echo "Hello World!"`.blob();
console.log(result); // Blob(13) { size: 13, type: "text/plain" }
```
## Builtin Commands
For cross-platform compatibility, Bun Shell implements a set of builtin commands, in addition to reading commands from the PATH environment variable.
- `cd`: change the working directory
- `ls`: list files in a directory
- `rm`: remove files and directories
- `echo`: print text
- `pwd`: print the working directory
- `bun`: run bun in bun
- `cat`
- `touch`
- `mkdir`
- `which`
- `mv`
- `exit`
- `true`
- `false`
- `yes`
- `seq`
- `dirname`
- `basename`
**Partially** implemented:
- `mv`: move files and directories (missing cross-device support)
**Not** implemented yet, but planned:
- See [Issue #9716](https://github.com/oven-sh/bun/issues/9716) for the full list.
## Utilities
Bun Shell also implements a set of utilities for working with shells.
### `$.braces` (brace expansion)
This function implements simple [brace expansion](https://www.gnu.org/software/bash/manual/html_node/Brace-Expansion.html) for shell commands:
```js
import { $ } from "bun";
await $.braces(`echo {1,2,3}`);
// => ["echo 1", "echo 2", "echo 3"]
```
### `$.escape` (escape strings)
Exposes Bun Shell's escaping logic as a function:
```js
import { $ } from "bun";
console.log($.escape('$(foo) `bar` "baz"'));
// => \$(foo) \`bar\` \"baz\"
```
If you do not want your string to be escaped, wrap it in a `{ raw: 'str' }` object:
```js
import { $ } from "bun";
await $`echo ${{ raw: '$(foo) `bar` "baz"' }}`;
// => bun: command not found: foo
// => bun: command not found: bar
// => baz
```
## .sh file loader
For simple shell scripts, instead of `/bin/sh`, you can use Bun Shell to run shell scripts.
To do so, just run the script with `bun` on a file with the `.sh` extension.
```sh#script.sh
echo "Hello World! pwd=$(pwd)"
```
```sh
$ bun ./script.sh
Hello World! pwd=/home/demo
```
Scripts with Bun Shell are cross platform, which means they work on Windows:
```powershell
> bun .\script.sh
Hello World! pwd=C:\Users\Demo
```
## Implementation notes
Bun Shell is a small programming language in Bun that is implemented in Zig. It includes a handwritten lexer, parser, and interpreter. Unlike bash, zsh, and other shells, Bun Shell runs operations concurrently.
## Credits
Large parts of this API were inspired by [zx](https://github.com/google/zx), [dax](https://github.com/dsherret/dax), and [bnx](https://github.com/wobsoriano/bnx). Thank you to the authors of those projects.