thlmulti

Tabs for your terminal. Not tmux. Not zellij. ~1700 lines of Go.

Mac Alacritty does Ctrl+T — new tab, same window. Linux Alacritty does not. Zellij does, but zellij is a whole world, and its mouse wheel stops scrolling the moment you click. So: four features, nothing else.

1. New tab, same window. Ctrl+T. Starts in the folder you are standing in.
2. Tab by number. Ctrl+1..Ctrl+9, Ctrl+0 for the tenth. Click tabs too. Ctrl+Shift+W closes one.
3. Wheel always scrolls. Click and scroll at once still scrolls. Drag over text, let go, it is in the clipboard. No mode, no prefix key.
4. Paste key is yours. Ctrl+Alt+V by default. Plain Ctrl+V is left alone, so vim's visual block still works.

No splits. No panes. No sessions. No detach. No plugins. No layout files.

Needs

• Go 1.27+ to build, go-task for the Taskfile.
• A terminal that speaks the Kitty keyboard protocol (Alacritty 0.15+). Without it Ctrl+<digit> looks identical to a bare digit and tab switching cannot work. Everything else still does.
• A terminal that speaks OSC 52, for copy. Alacritty does.
• wl-paste or xclip, for paste. Terminals refuse to let a program read the clipboard, so we ask the system instead.

Build

task build      # ./thlmulti
task install    # ~/.local/bin/thlmulti   (PREFIX=/usr/local task install)
task config     # ~/.config/thlmulti/config, keeps one that exists
task check      # gofmt, vet, test
task            # list everything

Point Alacritty at it

Back up the file first, then run task alacritty and paste what it prints:

[terminal.shell]
program = "/home/you/.local/bin/thlmulti"
args = []

Alacritty starts thlmulti, thlmulti starts your shells. Shell flags like --login go in the thlmulti config now, not in alacritty.toml. To undo it, put your backup back.

Config

~/.config/thlmulti/config. No file is fine — defaults apply. One name = value per line, # is a comment. An unknown name is an error, so a typo does not go quiet. config.example lists every setting.

Keys

Setting	Default
new_tab	ctrl+t	open a tab
close_tab	ctrl+shift+w	close it
paste	ctrl+alt+v	paste the clipboard
tab_mods	ctrl	modifier for tab-by-number

Chords look like ctrl+alt+v. Modifiers: ctrl, alt, shift, super. The key is a single character. none switches a binding off.

Why the odd defaults:

• Not ctrl+w to close — that deletes a word in zsh, far too useful to steal.
• Not ctrl+shift+v to paste — Alacritty already owns it and pastes on its own, so the key would never reach us.
• Not ctrl+v to paste — that is vim's visual block.

tab_mods must carry a modifier. Without one, a bare 1 would switch tabs and you could not type a digit, so it is refused.

Shell

shell = /bin/zsh --login

First word is the program, the rest are flags. Defaults to $SHELL.

Scrollback

scrollback = 2000

Lines of history per tab; 0 keeps none.

History is stored as whole rows at full width — 88 bytes a cell, trailing blanks included — so a line costs columns * 88 bytes whatever is printed on it. That is 17 KB a line at 200 columns, and it is per tab. Nothing out here can change it: it is the emulator's own data structure.

What can be changed is everything the history has already been. Pushing lines through a history that is full allocates several times what it holds, and Go hangs on to what it drops, ready for the next burst. thlmulti hands that back once nothing has happened for five seconds — collecting a big heap costs tens of milliseconds, so it waits for a moment when nobody is waiting on it. Measured on one tab, 200 columns, 60000 lines pushed through it:

scrollback	RSS during the flood	once it goes quiet	history alone
0	15 MB	12 MB	0 MB
2000 (default)	105 MB	62 MB	34 MB
20000	1013 MB	397 MB	336 MB

go test -run Reclaim -v . prints that table on your machine.

The middle column is a peak, not a resting state, and the right-hand one is the floor: history you asked to keep, and it is not going anywhere while you can still scroll to it. A wider window pays more for the same line count — 20000 lines is 134 MB at 80 columns and 503 MB at 300.

Ten tabs at 20000 is still not a thing you can have. The emulator's own default was 10000; this is 2000, same as tmux. Raise it if you need it — now you know the price.

Colours

thlmulti only paints the tab bar. The terminals inside the tabs paint themselves.

theme = auto

auto asks the terminal whether it is dark or light and follows. A terminal that will not answer gets the dark palette. One that changes theme while running gets repainted. Write dark or light to stop it guessing.

Pin any part by hand; whatever you leave out follows the theme.

Setting
tab_fg, tab_bg	tabs not in front, separators, the rule
active_fg, active_bg	the tab in front
toast_fg, toast_bg	"Copied to clipboard"
error_fg, error_bg	something failed

Values: default, a colour name (black…white, bright-black… bright-white, which use your palette), an index 0–255, or #rrggbb.

theme     = dark
active_bg = #1d2021
active_fg = bright-white

Mouse

• Drag over text, let go — copied. No key needed.
• Wheel scrolls history. Inside a full-screen program it becomes arrow keys, so it scrolls the thing you are looking at.
• Click a tab to switch.
• Programs that ask for the mouse (vim, k9s) get it. Hold Shift to take it back for Alacritty's own selection.
• A drag that wanders up onto the tab bar still belongs to the terminal, so the release is not lost and the selection does not get stuck. That was a bug once; a test guards it now.

Things worth knowing

TERM. Children get xterm-kitty only if that terminfo entry actually exists on the machine, otherwise xterm-256color. A TERM with no terminfo behind it makes zsh's line editor redraw blind — the prompt vanishes and every backspace leaves a staircase of garbage.

The scrollback hack. vaxis hardcodes 10000 lines and exposes no knob, so scrollback.go reaches in with reflect and sets the field. Ugly. The alternative was carrying a 9000-line fork of the emulator for one integer. Every field is checked by name and kind, so a vaxis upgrade that moves it reports an error in the tab bar instead of silently doing nothing.

Layout

main.go         tabs, key and mouse routing, the tab bar, the event loop
config.go       ~/.config/thlmulti/config
theme.go        tab bar colours, auto dark/light
scrollback.go   the history limit
clipboard.go    reading the clipboard (wl-paste, xclip)
cwd.go          the shell's folder, from /proc, for a new tab
terminfo.go     picking a TERM that has terminfo behind it
demo/           records docs/demo.gif; a module of its own, so a font
                rasteriser is not a dependency of the terminal

Tests

task test. resize_integration_test.go builds the real binary, runs it under a pty, grows the window and checks it repaints at the new width. That bug got past the unit tests three times — keep the test.