shalkboard : a terminal based chalkboard written in Bash

shalkboard is a chalkboard-like application working within any xterm compatible virtual terminal. The idea is to demonstrate that it is possible to build a complex interactive application completely written in Bash 3.2 without any kind of library or framework.

Why?

I was having fun parsing virtual terminal escape sequences when my son saw that I was actually drawing by clicking in the terminal. He asked me if it was possible to change the color, the first of a list of requirement that finally got me writing this little piece of code.

And, why Bash 3.2? Simply because it is the default Bash interpreter on MacOS. It would have been easier to work with Bash 5, but I wanted to write something that could work virtually everywhere.

Features

With shalkboard, it is actually possible to

• draw with four kind of brush,
• write text with 3 custom fonts,
• copy and paste a region of the page,
• undo the last action or the last group of actions,
• reload a page from file,
• save a page to file,
• redraw the current page.

As shalkboard only rely on terminal escape sequences that are supported by tmux, sharing a tmux session enables real-time collaborative drawing.

Usage

# From project's root, do
./shalkboard.sh demo/demo.board

Install

In order to run it anywhere without this source tree, compiling is actually compressing all the sourced files into one script that unzips itself before execution.

# Compile
make bin/shalkboard

# Install
sudo install bin/shalkboard /usr/local/bin/

# Run
shalkboard demo/demo.board

Uninstall

sudo rm /usr/local/bin/shalkboard

Running tests

To run all tests :

make test

References

• XTerm Control Sequences: This document describes all control sequences supported by xterm.

• vttest: As described by Wikipedia, vttest is an application that is used to demonstrate features of VT100 and related terminals, or emulations thereof, such as xterm.

  With the -l flag, this tool will also log requests and responses to vttest.log. It was quite useful to see what was expected by the terminal and what should be expected from it.