cli50 is a command-line tool via which you can (easily!) mount a directory within a container running cs50/cli, a Docker image based on Ubuntu 20.04, a popular distribution of Linux. We use cli50 to work on CS50’s own apps in a standard, contained environment, without having to install apps’ dependencies on our own Macs and PCs. It provides a command-line environment similar, but not quite identical to, a terminal window on CS50 IDE.


  1. Install Docker, if you haven’t already.

  2. Install Python 3.6 or later, if you haven’t already.

  3. Install pip, if you haven’t already.

  4. Install cli50 itself:

    pip3 install cli50


pip install --upgrade cli50


usage: [-h] [-d DOTFILE] [-f] [-j] [-l [CONTAINER]] [-S] [-t TAG] [-u] [-V] [DIRECTORY]

positional arguments:
  DIRECTORY             directory to mount, else $PWD

optional arguments:
  -h, --help            show this help message and exit
  -d DOTFILE, --dotfile DOTFILE
                        dotfile in your $HOME to mount read-only in container's $HOME
  -f, --fast            skip autoupdate
  -j, --jekyll          serve Jekyll site
  -l [CONTAINER], --login [CONTAINER]
                        log into CONTAINER
  -S, --stop            stop any containers
  -t TAG, --tag TAG     start cs50/cli:TAG, else cs50/cli:latest
  -u, --update          update only
  -V, --version         show program's version number and exit


Mount current working directory


Your current working directory will be mounted in /mnt within the container.

Mount any directory

Assuming path/to/directory is that directory’s absolute path, you can mount it within the container as follows:

cli50 path/to/directory

The directory will be mounted in /mnt within the container.

Mount dotfile

You can additionally mount a dotfile (or any other file or directory) read-only in $HOME within the container as follows:

cli50 ~/.file

For instance, it might be useful to mount one’s own .bashrc:

cli50 -d ~/.bashrc

Or one’s .ssh directory, so that you can use your own SSH keys within the container:

cli50 -d ~/.ssh

Skip autoupdate

By default, cli50 autoupdates (i.e., pulls) cs50/cli, the Docker image on which it’s based, which can be time-consuming on slow internet connections. You can skip autoupdate as follows:

cli50 -f

Update only

You can update (i.e., pull) cs50/cli, the Docker image on which cli50 is based, without actually starting a container as follows:

cli50 -u

Log into running container

If a container (based on any Docker image, cs50/cli or otherwise) is already running, you can spawn a login shell within it as follows:

cli50 -l

If multiple containers are running, you’ll be asked, yes or no, in reverse-chronological order, into which container you’d like to log in.

Mount ~/.* in container’s $HOME

You can mount, read-only, a dotfile that’s in your $HOME (e.g., ~/.vimrc) inside of a container’s $HOME as follows:

cli50 -d .vimrc

Directories (e.g., ~/.vim) are supported as well:

cli50 -d .vim

Serve Jekyll site

When developing a Jekyll site, you can serve (and continually rebuild) it within a container as follows:

cli50 -j

The site will be served at within the container, but port 8080 will be published on pseudorandom port on the host (i.e., your computer). If cli50 outputs, e.g.,>8080/tcp, ...

on startup, you can access the site at on your computer.