Problem set 0 #

Regardless of your computer’s operating system, you’ll be interacting with it using the Unix command line (also called the terminal).

What is Unix? #

Unix is a family of operating systems originally developed at Bell Labs in the 1970s by Ken Thompson and Dennis Ritchie. While operating systems have many newer user interface features, some of the original features from Unix remain the most useful for programming work in CS 51.

Users of the earliest Unix systems interacted with their computers exclusively through the keyboard, via the command line. They would type commands (names of short programs) that directed the computer to take action, like running a program to switch to a different folder or create a text file.

If you took CS 50, you ran commands in the command line on the CS 50 IDE. You will spend a good deal of time at the command line in CS 51, and comfort with it, developed over time, will be one of the skills you build in this course.

Accessing the Command Line #

On macOS: Search for Terminal in Spotlight or look in Applications > Utilities. Launch it to get a terminal window with a command line prompt.

On Linux/Ubuntu: Right-click on the desktop and select Open Terminal.

On Windows: After setting up your Ubuntu VM (see Windows setup section below), you’ll access the command line from within Ubuntu.

Basic Commands #

At the command line prompt (we use % to represent the prompt), you can type commands. Here are some essential ones:

man - View the manual for any command

% man mkdir

Type q to exit the manual.

ls - List files and directories in the current location

% ls

cd - Change directory (move to a different folder)

% cd Documents        # Move into Documents folder
% cd ..              # Move up one level

mkdir - Make a new directory

% mkdir testdirectory

rm - Remove a file (be careful!)

% rm filename.txt

These ‘‘commands’’ are actually programs. You can run them with many different options (check man ls for examples).

For more guidance, see this command line tutorial.

Because Windows is not a Unix-based operating system, we recommend installing an Ubuntu Linux virtual machine (VM) to get access to a Unix command line.

Installing VMware and Ubuntu #

1. Get VMware Workstation (free for Harvard students):

   • Fill out this Google form requesting VMware Workstation 15
   • Use your Harvard email address
   • Wait for approval (may take up to a day)
   • Download and install VMware from the WebStore

2. Download Ubuntu:

   • Get Ubuntu 22.04 LTS from ubuntu.com
   • Note: Ubuntu is free, no donation needed

3. Create Ubuntu VM in VMware:

   • Launch VMware Workstation
   • Go to Edit → Preferences → Display → check “Autofit guest”
   • File → New Virtual Machine → Typical
   • Select “Installer disc image file” and choose the Ubuntu .iso you downloaded
   • Set username and password
   • Set disk size to 20GB minimum, “Split virtual disk into multiple files”
   • Finish and let Ubuntu install (takes a few minutes)

4. After Ubuntu starts:

   • Log in with your password
   • Skip the “What’s new” screens
   • Select “No, don’t send system info” when asked

5. Run the setup command:

   • Right-click on desktop → Open Terminal
   • Run the automated setup command:

     curl -fsSL https://raw.githubusercontent.com/cs51/setup/main/cs51_install.sh | bash
     

If the automated setup script fails for any reason, you can install everything manually.

Background: The Unix Command Line #

You’ll be interacting with your computer using the Unix command line. On macOS, use the Terminal application (in Applications → Utilities). On Linux/Ubuntu, right-click the desktop and select “Open Terminal”.

The command line prompt is typically % or $. We use % in our examples.

Installing Package Managers #

On macOS:

1. Install Homebrew:

   • Visit brew.sh and follow the installation instructions
   • Verify: brew (should show help menu)

2. Install XQuartz (for graphics):

   brew install xquartz
   

3. Install opam:

   brew install pkg-config
   brew install gpatch
   brew install opam
   

4. Restart your computer

On Linux:

1. Update package list:

   sudo apt-get update -y
   

2. Install build tools and dependencies:

   sudo apt-get install -y gcc make patch unzip m4 git xorg libx11-dev libxft-dev pkg-config opam libgmp-dev
   

Setting up OCaml #

1. Initialize opam:

   opam init -a
   

   Close and reopen your terminal.

2. Create CS51 switch with OCaml 5.2.1:

   opam update
   opam switch create cs51 5.2.1
   opam switch cs51
   

3. Install required packages:

   opam install -y graphics
   opam install -y dune
   opam install -y cppo  
   opam install -y menhir
   opam install -y yojson
   opam install -y utop
   opam install -y merlin
   

4. Install CS51 utilities:

   opam pin add https://github.com/cs51/utils.git -y
   opam pin add https://github.com/cs51-staff/ANSITerminal.git -y
   

5. Update environment:

   eval $(opam env)
   

6. Restart your computer

Installing Visual Studio Code #

On macOS:

brew install --cask visual-studio-code

On Linux:

sudo apt-get install -y software-properties-common apt-transport-https wget gpg
wget -qO- https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor | sudo tee /usr/share/keyrings/packages.microsoft.gpg > /dev/null
ARCH=$(dpkg --print-architecture)
echo "deb [arch=${ARCH} signed-by=/usr/share/keyrings/packages.microsoft.gpg] https://packages.microsoft.com/repos/code stable main" | sudo tee /etc/apt/sources.list.d/vscode.list
sudo apt-get update
sudo apt-get install -y code

After installation, verify that OCaml graphics is working properly:

cs51-graphics-check

You should see a small window with a white exclamation mark on a red background. Click the window and press any key to close it. If it works, you’re all set!

If graphics doesn’t work on macOS:

1. Verify X11 libraries exist:

   find /opt -name libX11.6.dylib
   

   Should find /opt/X11/lib/libX11.6.dylib

2. If not found, reinstall XQuartz:

   brew install xquartz
   

   Then restart your computer and retry.

3. If still not working, reinstall graphics package:

   opam uninstall graphics
   opam install graphics
   

   Restart your computer and retry.

4. If still failing, manually link libraries:

   cd
   mkdir lib
   cd lib
   ln -s /opt/X11/lib/libX11.6.dylib libX11.6.dylib
   

   Restart your computer and retry.

If graphics doesn’t work on Windows/Ubuntu VM:

If you see an error like Fatal error: exception Graphics.Graphic_failure("Cannot open display") or cs51-graphics-check stalls indefinitely:

1. Download and install VcXsrv:

   • Download from SourceForge
   • Install on your Windows host (not in the Ubuntu VM)

2. Configure VcXsrv:

   • Follow the instructions in this video
   • Key settings: Enable “Disable access control”

3. Restart and test:

   • Restart your Ubuntu VM
   • Try cs51-graphics-check again

If issues persist, contact course staff for assistance.