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Scripting tmux

Everything you can do with keys, you can do from the command line — and that means you can do it from a script. This is where tmux graduates from "handy" to "infrastructure": whole workspace layouts launched with one command, no nohup required.

The core idea

tmux commands take a target (-t) naming the session/window/pane. So instead of pressing keys inside tmux, you run:

tmux new-session -d -s duels            # -d: don't attach, just create
tmux split-window -h -t duels
tmux send-keys -t duels:0.0 'htop' Enter

That builds, detached: a session duels, split side-by-side, with htop running in the left pane. Attach whenever:

tmux attach -t duels

Check (verified on tmux 3.4):

tmux new-session -d -s verify -x 200 -y 50
tmux split-window -h -t verify
tmux send-keys -t verify:0.0 'echo hello-from-pane-0' Enter
sleep 1
tmux capture-pane -t verify:0.0 -p | grep hello

hello-from-pane-0

capture-pane -p prints a pane's contents — handy for checking on things without attaching.

A real example: the duel batch

Instead of nohup python3 ollama_duel.py ... & and hoping the SSH session survives, launch it in a named session:

#!/bin/bash
# start-duels.sh
tmux kill-session -t duels 2>/dev/null   # clean slate if rerun
tmux new-session -d -s duels -n batch \
  'cd ~/dual && python3 ollama_duel.py --profile arduino_q scenarios/'
tmux split-window -h -t duels
tmux send-keys -t duels:0.1 'tail -f ~/dual/runall.log' Enter

One command, and you get: the batch running in the left pane, its log tailing in the right pane, all in a session that survives your laptop closing. Attach with tmux attach -t duels; detach with Ctrl-b d.

Target syntax

Targets look like session:window.pane:

  • duels — the session (first window, first pane implied)
  • duels:1 — window 1 of session duels
  • duels:0.1 — pane 1 of window 0

You can usually abbreviate: if there's only one session, -t 0.1 is enough.

send-keys gotchas

  • send-keys types literally — to "press Enter," pass Enter as a separate argument (a key name, not the character).
  • Quote the whole command: send-keys -t s 'cd ~/dual' Enter sends the text, then the key.
  • It types into whatever is currently in the pane — if a program is waiting at a prompt, your keys go there. Make sure the pane is at a shell prompt first.

When scripting beats keys

  • Repeatable setups — "every morning I open these four things" becomes one script.
  • Remote launches — ssh box ./start-duels.sh, close the laptop, done. The session outlives the SSH connection.
  • Handoffs — a script documents the layout; keystrokes don't.