tmux

Interact with tmux sessions using the tmux CLI and the bundled read-tmux and send-tmux helper scripts. The scripts live at {baseDir}/scripts/ — substitute the skill's base directory when invoking them.

Resolve pane_id first

Before doing anything with a pane, resolve its pane_id. This stable, unambiguous handle survives window/session renames — and since a recreated pane gets a new pane_id, using it automatically treats recreated panes as new sessions.

# From a user-supplied index (e.g. "pane 1" in the current window)
PANE_ID=$(tmux display-message -t :.1 -p '#{pane_id}')   # → %42

# From a full target
PANE_ID=$(tmux display-message -t 0:2.1 -p '#{pane_id}')

# pane_id works as -t for all pane-level commands
tmux send-keys -t %42 "echo hello" Enter
tmux capture-pane -t %42 -p
tmux select-pane -t %42 -T "my title"
tmux kill-pane -t %42

Finding a pane from an informal description

The user may say "the other pane", "the pane running vim", "the shell on the right". Resolve these yourself before asking:

# All panes in current window, excluding your own
tmux list-panes -F '#{pane_id} #{pane_current_command}' | grep -v "^$TMUX_PANE "

# "The other pane" — works when there are exactly 2 panes
PANE_ID=$(tmux list-panes -F '#{pane_id}' | grep -v "^$TMUX_PANE$")

# "The pane running vim"
PANE_ID=$(tmux list-panes -F '#{pane_id} #{pane_current_command}' | grep vim | awk '{print $1}')

$TMUX_PANE is set automatically by tmux — it's your own pane ID.

If the description is still ambiguous, show numbered overlays:

tmux display-panes -d 5000   # numbered overlays appear for 5 seconds
# ask the user which number, then resolve
PANE_ID=$(tmux display-message -t :.N -p '#{pane_id}')

Reading output

Use read-tmux, not raw tmux capture-pane. The script tracks position between calls so you only receive new output, and it handles TUI apps separately from shell panes.

{baseDir}/scripts/read-tmux %42          # shell panes — delta since last read
{baseDir}/scripts/read-tmux --tui %42    # TUI apps (vim, htop, etc.) — diff of changed screen regions
{baseDir}/scripts/read-tmux --full %42   # TUI — always show full screen, no diff

Delta mode (default):

First call: captures full scrollback up to cursor, saves position
Subsequent calls: only new lines since last read
No new output: prints (no new output)

TUI mode (--tui):

First call: captures full visible screen, saves snapshot
Subsequent calls: unified diff if ≤50% of lines changed; full screen otherwise
No changes: prints (no changes on screen)

Output is capped at first 2000 + last 2000 bytes. State lives in /tmp/tmux-skill/<pane_id>/.

Sending keys

Use send-tmux — it decorates the pane and forwards all arguments to tmux send-keys.

{baseDir}/scripts/send-tmux %42 "npm test" Enter   # run a command
{baseDir}/scripts/send-tmux %42 C-c                # interrupt
{baseDir}/scripts/send-tmux %42 C-d                # EOF / exit shell
{baseDir}/scripts/send-tmux %42 q                  # quit a pager

Pane decoration

Both read-tmux and send-tmux auto-decorate panes on first use — a yellow "● Operated by Claude" bar appears at the top. No manual setup needed.

To release when done:

tmux set-option -p -t %42 -u pane-border-status 2>/dev/null || true
tmux set-option -p -t %42 -u pane-border-format 2>/dev/null || true

Sessions

tmux list-sessions
tmux list-sessions -F '#{session_name} (#{session_windows} windows)'
tmux new-session -d -s <name> [-c <start-dir>]
tmux rename-session -t <old> <new>
tmux kill-session -t <name>
tmux has-session -t <name> 2>/dev/null && echo exists

Windows

tmux list-windows -t <session>
tmux list-windows -t <session> -F '#{window_index}: #{window_name}'
tmux new-window -t <session> -n <name> [-c <dir>]
tmux rename-window -t <session>:<index> <new-name>
tmux move-window -s <session>:<index> -t <dst-session>:<new-index>
tmux swap-window -s <session>:<a> -t <session>:<b>
tmux kill-window -t <session>:<index>

Panes

# List
tmux list-panes -t <session>:<window> -F '#{pane_index} #{pane_id} #{pane_current_command}'
tmux list-panes -a -F '#{session_name}:#{window_index}.#{pane_index} #{pane_id} #{pane_current_command}'

# Create — split relative to your own pane so it opens in the right window
PANE_ID=$(tmux split-window -h -t "$TMUX_PANE" -P -F '#{pane_id}')   # side by side
PANE_ID=$(tmux split-window -v -t "$TMUX_PANE" -P -F '#{pane_id}')   # top/bottom

tmux select-pane -t %42 -T <title>
tmux move-pane -s %42 -t <dst-session>:<dst-window>
tmux break-pane -t %42 -n <new-window-name>
tmux join-pane -s <src-window> -t <dst-window>
tmux swap-pane -s %42 -t %99
tmux kill-pane -t %42

Querying state

tmux display-message -t %42 -p '#{pane_id}'
tmux display-message -t %42 -p '#{pane_current_command}'
tmux display-message -t %42 -p '#{pane_current_path}'
tmux display-message -t %42 -p '#{pane_pid}'

Useful format variables: #{pane_id}, #{pane_index}, #{pane_current_command}, #{pane_current_path}, #{pane_pid}, #{session_name}, #{window_index}, #{window_name}

Patterns

Wait for a command to finish

{baseDir}/scripts/send-tmux %42 "make build && echo __DONE__" Enter
while ! {baseDir}/scripts/read-tmux %42 | grep -q "__DONE__"; do sleep 0.5; done

Open a new pane for a task

WINDOW=$(tmux new-window -t myproject -n build -P -F '#{window_index}')
PANE_ID=$(tmux display-message -t "myproject:${WINDOW}.0" -p '#{pane_id}')
{baseDir}/scripts/send-tmux "$PANE_ID" "make build" Enter

Interrupt and re-run

{baseDir}/scripts/send-tmux %42 C-c
sleep 0.2
{baseDir}/scripts/send-tmux %42 "make build" Enter