bun.sh/docs/runtime/shell.md

Bun Shell makes shell scripting with JavaScript & TypeScript fun. It's a cross-platform bash-like shell with seamless JavaScript interop.

{% callout type="note" %} Alpha-quality software: Bun Shell is an unstable API still under development. If you have feature requests or run into bugs, please open an issue. There may be breaking changes in the future. {% /callout %}

Quickstart:

import { $ } from "bun";

const response = await fetch("https://example.com");

// Use Response as stdin.
await $`echo < ${response} > wc -c`; // 120

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.

Getting started

The simplest shell command is echo. To run it, use the $ template literal tag:

import { $ } from "bun";

await $`echo "Hello World!"`; // Hello World!

By default, shell commands print to stdout. To quiet the output, call .quiet():

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():

import { $ } from "bun";

// .text() automatically calls .quiet() for you
const welcome = await $`echo "Hello World!"`.text();

console.log(welcome); // Hello World!\n

To get stdout, stderr, and the exit code, use await or .run:

import { $ } from "bun";

const { stdout, stderr, exitCode } = await $`echo "Hello World!"`.quiet();

console.log(stdout); // Buffer(6) [ 72, 101, 108, 108, 111, 32 ]
console.log(stderr); // Buffer(0) []
console.log(exitCode); // 0

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:

import { $ } from "bun";

const buffer = Buffer.alloc(100);
const result = await $`echo "Hello World!" > ${buffer}`;

console.log(result.exitCode); // 0
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:

import { $, file } 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

import { $ } from "bun"

await $`cat < myfile.txt`

Example: Redirect stdout -> file

import { $ } from "bun"

await $`echo bun! > greeting.txt`

Example: Redirect stderr -> file

import { $ } from "bun"

await $`bun run index.ts 2> errors.txt`

Example: Redirect stdout -> stderr

import { $ } from "bun"

// redirects stderr to stdout, so all output
// will be available on stdout
await $`bun run ./index.ts 2>&1`

Example: Redirect stderr -> stdout

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:

import { $ } from "bun";

const result = await $`echo "Hello World!" | wc -w`.text();

console.log(result); // 2\n

You can also pipe with JavaScript objects:

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

Environment variables

Environment variables can be set like in bash:

import { $ } from "bun";

await $`FOO=foo bun -e 'console.log(process.env.FOO)'`; // foo\n

You can use string interpolation to set environment variables:

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:

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():

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:

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:

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():

import { $ } from "bun";

await $`pwd`.cwd("/tmp"); // /tmp

You can change the default working directory for all commands by calling $.cwd:

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():

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():

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():

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:

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():

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

Partially implemented:

• mv: move files and directories (missing cross-device support)

Not implemented yet, but planned:

• mkdir: create directories
• cp: copy files and directories
• cat: concatenate files

Utilities

Bun Shell also implements a set of utilities for working with shells.

$.braces (brace expansion)

This function implements simple brace expansion for shell commands:

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:

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:

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.

echo "Hello World! pwd=$(pwd)"

$ bun ./script.sh
Hello World! pwd=/home/demo

Scripts with Bun Shell are cross platform, which means they work on Windows:

PS C:\Users\Demo> bun .\script.sh
Hello World! pwd=C:\Users\Demo

Credits

Large parts of this API were inspired by zx, dax, and bnx. Thank you to the authors of those projects.