Introducing Eat: A New Terminal Emulator for Emacs

November 25, 2022

Several hours ago, I published Eat on Codeberg. Eat stands for "Emulate A Terminal." As the name suggests, it's a new terminal emulator for Emacs.

How It Started

I have used all three terminal emulators that I know to exist. These are Term, Coterm and Vterm. I don't like Term's keybindings in char mode, and it sometimes messes up thing when in line mode. Coterm is great, but I'm not a Shell mode fanboy, so that also doesn't fit for me. Vterm is a fully-featured terminal powered by libvterm, but still I don't like Vterm. Perhaps that because it doesn't have a char mode by default, or maybe something else that I don't know myself.

So I started writing Eat. At first it was really just for fun project. But, as I implemented more and more things, I found that Eat is actually a bit faster than the other terminal emulator written in Emacs Lisp, despite I didn't wrote Eat with performance in mind. So, I started to take it seriously and optimized as much as I can. I also tried to make the terminal emulation code as much reusable as possible.


Eat's main feature is Eshell integration. I use Eshell as my primary shell, so I kept the terminal emulation code reusable to implement a terminal in Eshell. As the terminal emulation code is shared, both Eat's own terminal UI and Eshell integration has same features despite the UIs being different.

To be honest, Eat doesn't have too many features at the moment, partly because I don't need them, partly because I'm current focusing on more automated tests instead of new features. But Eat terminal emulator has four key features, complete mouse support, complete clipboard integration and decreased flickering and speed.

Just like other XTerm-like terminals, you can use mouse. All you have to do is use the mouse, nothing more. Mouse supporting programs will automatically get click, dragging and movement events, even when your Emacs is in the terminal.

Clipboard integration is also implemented. That means you can copy text in your Emacs and paste it in your terminal, or vice versa. However the program in your terminal can't get your clipboard or kill ring content unless you yank (paste) it with Emacs, that's disabled by default for security reasons.

Eat doesn't flicker much. On my computer, it is faster than Vterm, because Eat flickers way less than Vterm. If you want to know why, here it is: after some research, I discovered that programs send updates to terminal in parts, which causes flickering. Eat uses some stupid yet effective heuristics inspired by Suckless terminal to join the parts to show them all at once, reducing the number of redisplays. Redisplay is an expensive process, so skipping some redisplays means Eat gets that time to process more things. That's why Eat is faster that Vterm in many cases, when Vterm is wasting time doing useless redisplays, Eat is processing more things to display all at once.

Eat is reasonably fast, faster than any other Emacs Lisp terminal emulator. On my computer, Eat beats native-compiled Term even without byte compilation, and native-compiled Eat is almost five times faster than Term. Coterm is a great terminal in my opinion, both in terms of speed and in terms of code-readability. But Eat is faster than Coterm, around 1.4 to 1.9 times faster. Vterm's terminal emulator is actually a C library, so it's extremely hard to even come close to its speed. On my computer, Vterm is around 1.5 to two times faster, but since Vterm wastes time flickering, Eat usually faster in most non-trivial cases.


Eat is not available in any package archive, but if you do use Quelpa, I have this recipe for you:

(quelpa '(eat :fetcher git
              :url ""
              :files ("*.el" "dir"
                      "*.info" "*.texi"
                      "*.ti" ("e" "e/*")))