Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time


Build Status on npm

This module can help you if you like to emulate a bash shell in plain Javascript.

It might be useful for education purposes or even to ease the interaction with a back-end system.

bash-emulator implements an environment for bash commands to run in and it also includes some default commands. The system it provides can be thought of like the syscalls of an operating system. Shell commands are programs running on top of this low-level primitives.

The system doesn't handle any UI interaction but provides hooks to communicate with other systems. It's easy to add new commands and customize the underlying file system.

Also note that even though we try to create a realistic bash environment, this system won't behave identical to your local environment. Before using commands for other projects you should also try them with a real shell.

If you are looking for a real terminal to run in your browser, have a look at xterm.js.


The module can be used in Node.js or in the browser. Get it with:

npm install --save bash-emulator

Example usage

The module exports one function that can be required from another module. Please use a tool like webpack or browserify for bundling and minification in your own workflow.

bashEmulator(state) -> emulator

  • state an optional object to initialize the state. For shape see below.
  • Returns an emulator object


  • run(command) -> Promise(output, code)
    • command a bash command as string
    • Returns a Promise that resolves with an output string.
  • getDir() -> Promise(path)
    • Returns a Promise that resolves with the current working directory
  • changeDir(path) -> Promise
    • path relative path to set working directory to
    • Returns a Promise that resolves when change is done
  • read(filePath) -> Promise(content)
    • filePath relative path of file to read
    • Returns a Promise that resolves with the content of the file
  • readDir(path) -> Promise([files])
    • path optional, relative path of directory to read. Defaults to current directory.
    • Returns a Promise that resolves with an array of file names.
  • stat(path) -> Promise(stats)
    • path optional path of file or directory. Defaults to current directory.
    • Returns a Promise that resolves with a stats object. For now, only property is modified.
  • createDir(path) -> Promise
    • path relative, non-existed path for new directory
    • Returns a Promise that resolves when directory is created
  • write(filePath, content) -> Promise
    • If file isn't empty, content is appended to it.
    • filePath path of file that should be written to. File doesn't have to exist.
    • Returns a Promise that resolves when writing is done
  • remove(path) -> Promise
    • path path of file or directory to delete
    • Returns a Promise that resolves when deleting is done
  • copy(source, destination) -> Promise
    • source path of file or directory to copy
    • destination target path. Will be overwritten if existent.
    • Returns a Promise that resolves when copying is done
  • getHistory() -> Promise([commands])
    • Returns a Promise that resolves with a array containing all commands from the past
  • completeUp(input) -> Promise(command)
    • Complete a command from history
    • Can be called multiple times to go further back in history
    • See example for connecting arrow-keys with completion
    • str command that should be completed
    • Returns a Promise with a command, is undefined if no completion found
  • completeDown(input) -> Promise(command)
    • Move in opposite direction to completeUp
    • str command that should be completed
    • Returns a Promise with a command, is undefined if no completion found
  • commands
    • An object with all commands that the emulator knows of
  • state

Built-in features, commands and flags

  • pipes |
  • ls -l -a
  • cd
  • pwd
  • history
  • cat -n
  • touch
  • mkdir
  • mv -n
  • cp -r -R
  • rm -r -R
  • rmdir

The state object

It's not recommended to access the state directly. Use the above defined helper methods instead.

  • history an array of strings containing previous commands
  • user name of the current user (defaults to "user")
  • workingDirectory a string containing the current working directory (defaults to /home/user)
  • fileSystem an object that maps from absolute paths to directories or files.
    • Each value has a type property thats either 'dir' or 'file' and a modified property containing a unix timestamp
    • Files also have a content property.
    • Default file system contains only directories for /home/user

Storing state in localStorage

var state = JSON.parse(localStorage.bashEmulator || '{}')
var emulator = bashEmulator(state)
function saveState () {
  localStorage.bashEmulator = JSON.stringify(emulator.state)

Writing your own commands

You can modify the commands object of your emulator instance to your liking.

To add a new command you need to implement the following API:

var emulator = bashEmulator()
emulator.commands.myCommand = function (env, args) {}
  • env object with:
    • output(string) call to write a string to stdout
    • error(string) call to write a string to stderr
    • exit(code) call to exit command.
      • code integer to mark state of exit. Failure when not 0 (optional)
    • system reference to the emulator object.
  • args array from command string. First element is command name.
  • Optionally return object to register handlers for events: { input: fn, close: fn }

Using a custom file system

You can ignore the simple, built-in file system and overwrite all required methods of your emulator instance with custom implementations. The API of the methods are designed to work with asynchronous implementations as well.


  • Make sure you have node.js installed
  • Setup project using npm install
  • Make sure tests are passing using npm test
  • Build the bash-emulator.min.js file with npm run build


We are happy to accept new contributions!

It can be a fun experience to re-implement some programs you already know. This can give you some new insights in how they work. You can also try out strace to find out how commands work on your local system!

Just make sure the tests are passing (npm test) and send a Pull Request.

If you are looking for a new feature to implement, make sure to have a look at our roadmap.

Browser Support

To support IE, please use a promise polyfill. For example:




Emulate a bash environment in plain JS. In your browser.







No releases published


No packages published