tmux

name	tmux
description	Use only when you need to run interactive CLI tools (Python REPL, etc.) that require real-time input/output OR when asked to use tmux

Using tmux for Interactive Commands

CRITICAL SAFETY RULES

NEVER kill a tmux session without EXPLICIT permission from the user.

You may ONLY kill a session if BOTH conditions are met:

1. You created the session in the current conversation
2. The user explicitly grants permission to kill it

Default behavior: ALWAYS detach, NEVER kill.

Existing sessions may contain important work. Destroying them can cause data loss.

Overview

Interactive CLI tools (vim, interactive git rebase, REPLs, etc.) cannot be controlled through standard bash because they require a real terminal. tmux provides detached sessions that can be controlled programmatically via send-keys and capture-pane.

When to Use

Use tmux when:

• Running vim, nano, or other text editors programmatically
• Controlling interactive REPLs (Python, Node, etc.)
• Handling interactive git commands (git rebase -i, git add -p)
• Working with full-screen terminal apps (htop, etc.)
• Commands that require terminal control codes or readline

Don't use for:

• Simple non-interactive commands (use regular Bash tool)
• Commands that accept input via stdin redirection
• One-shot commands that don't need interaction

Quick Reference

Task	Command
List sessions	tmux list-sessions
List windows	tmux list-windows -t <session>
Attach to session	tmux attach -t <session>
Create window	tmux new-window -t <session>: -n <name> <command>
Switch window	tmux select-window -t <session>:<index>
Send input	tmux send-keys -t <session>:<index> 'text' Enter
Capture output	tmux capture-pane -t <session>:<index> -p
Detach	tmux detach-client -s <session>

Core Pattern

Before (Won't Work)

# This hangs because vim expects interactive terminal
bash -c "vim file.txt"

After (Works)

# Check for existing session, create if needed
if ! tmux has-session -t mywork 2>/dev/null; then
  tmux new-session -d -s mywork
fi

# Create window (numbered 1, 2, 3, etc.)
tmux new-window -t mywork: -n editor vim file.txt
sleep 0.3

# Get window index (windows are numbered, not named)
INDEX=$(tmux list-windows -t mywork -F '#{window_index} #{window_name}' | grep editor | cut -d' ' -f1)

# Send commands using window index
tmux send-keys -t mywork:$INDEX 'i' 'Hello World' Escape ':wq' Enter

# Capture output
tmux capture-pane -t mywork:$INDEX -p

# Detach when done (session persists)
tmux detach-client -s mywork

Implementation

Basic Workflow

1. List existing sessions to see what's available
2. Connect to or create session - reuse existing sessions when possible
3. Create window - each window gets a numbered index (1, 2, 3...)
4. Wait briefly for initialization (100-500ms depending on command)
5. Send input using window index session:N
6. Capture output using window index
7. Detach when done - session stays alive for later

Special Keys

Common tmux key names:

• Enter - Return/newline
• Escape - ESC key
• C-c - Ctrl+C
• C-l - Ctrl+L (clear screen)
• C-b - tmux prefix (for manual navigation)
• Up, Down, Left, Right - Arrow keys
• Space - Space bar
• BSpace - Backspace

Session Management

List all sessions:

tmux list-sessions
# Output: session_name: N windows (created ...) (attached)

Connect to existing or create:

if ! tmux has-session -t dev 2>/dev/null; then
  tmux new-session -d -s dev
fi

Window Management

Windows are numbered starting from 0 or 1. Names are labels, not unique identifiers.

Create window:

# Creates a numbered window with optional name
tmux new-window -t mysession: -n myname vim file.txt

List windows:

tmux list-windows -t mysession
# Output: 1: zsh (1 panes) ...
#         2: vim- (1 panes) ...
#         3: python* (1 panes) ... (active)

Get window index:

# By name (if you know it)
tmux list-windows -t mysession -F '#{window_index} #{window_name}' | grep vim

# Active window
tmux list-windows -t mysession -F '#{window_index} #{?window_active,(active),}' | grep active

Target windows by index:

# Always use index, never assume name is unique
tmux send-keys -t mysession:2 'echo hello' Enter
tmux capture-pane -t mysession:2 -p

Switch to window:

# Programmatically select window
tmux select-window -t mysession:2

# Or send prefix + number (if interacting)
tmux send-keys -t mysession C-b 2

Working Directory

Specify working directory when creating session or window:

# For session
tmux new-session -d -s git -c /path/to/repo

# For window
tmux new-window -t git: -n status -c /path/to/repo git status

Helper Wrapper

See tmux-wrapper.sh for simplified commands:

# List all sessions and windows
./tmux-wrapper.sh list

# Connect to existing or create new
./tmux-wrapper.sh connect dev

# Create window, returns its index
./tmux-wrapper.sh window dev editor vim file.txt
# Output: Window index: 2

# Send to window by index
./tmux-wrapper.sh send dev 2 'i' 'Hello' Escape ':wq' Enter

# Capture from window
./tmux-wrapper.sh capture dev 2

# Detach (recommended)
./tmux-wrapper.sh detach dev

Common Patterns

Multi-Window Development Session

# Connect to or create
if ! tmux has-session -t dev 2>/dev/null; then
  tmux new-session -d -s dev
fi

# Create windows (get their indices)
tmux new-window -t dev: -n editor vim file.txt
tmux new-window -t dev: -n repl python3 -i
tmux new-window -t dev: -n shell bash

# List windows to see indices
tmux list-windows -t dev -F '#{window_index}: #{window_name}'
# 1: editor
# 2: repl
# 3: shell

# Work in python window (index 2)
tmux send-keys -t dev:2 'import math' Enter
tmux send-keys -t dev:2 'print(math.pi)' Enter
tmux capture-pane -t dev:2 -p

# Switch to editor (index 1)
tmux select-window -t dev:1
tmux send-keys -t dev:1 'i' 'Code here' Escape ':wq' Enter

# Detach
tmux detach-client -s dev

Python REPL

if ! tmux has-session -t python 2>/dev/null; then
  tmux new-session -d -s python
fi

tmux new-window -t python: -n repl python3 -i
sleep 0.3

# Get window index
IDX=$(tmux list-windows -t python -F '#{window_index} #{window_name}' | grep repl | cut -d' ' -f1)

tmux send-keys -t python:$IDX 'import math' Enter
tmux send-keys -t python:$IDX 'print(math.pi)' Enter
tmux capture-pane -t python:$IDX -p

tmux detach-client -s python

Vim Editing

if ! tmux has-session -t edit 2>/dev/null; then
  tmux new-session -d -s edit
fi

tmux new-window -t edit: -n file1 vim /tmp/file.txt
sleep 0.3

IDX=$(tmux list-windows -t edit -F '#{window_index} #{window_name}' | grep file1 | cut -d' ' -f1)

tmux send-keys -t edit:$IDX 'i' 'New content' Escape ':wq' Enter
tmux detach-client -s edit

Common Mistakes

Using Window Names Instead of Indices

Problem: Window names are not unique identifiers

Fix: Always use window index

# ✗ Wrong - name might not be unique
tmux send-keys -t sess:editor 'text' Enter

# ✓ Correct - use index
IDX=$(tmux list-windows -t sess -F '#{window_index} #{window_name}' | grep editor | cut -d' ' -f1)
tmux send-keys -t sess:$IDX 'text' Enter

Not Waiting After Window Creation

Problem: Capturing immediately shows blank screen

Fix: Add brief sleep

tmux new-window -t sess: -n vim vim file.txt
sleep 0.3  # Let vim initialize

Forgetting Enter Key

Problem: Commands typed but not executed

Fix: Explicitly send Enter

tmux send-keys -t sess:2 'print("hello")' Enter

Killing Instead of Detaching

Problem: Session destroyed, can't reconnect, data loss

Fix: ALWAYS detach, NEVER kill without explicit permission

tmux detach-client -s sess    # ✓ ALWAYS do this
tmux kill-session -t sess     # ✗ FORBIDDEN without explicit permission

Remember: You may ONLY kill a session if:

1. You created it in this conversation, AND
2. User explicitly granted permission to kill it

When in doubt, detach.

Not Checking Session Exists

Problem: Creating duplicate sessions fails

Fix: Check first

if ! tmux has-session -t dev 2>/dev/null; then
  tmux new-session -d -s dev
fi

Real-World Impact

• Enables programmatic control of vim/nano for file editing
• Allows automation of interactive git workflows (rebase, add -p)
• Makes REPL-based testing/debugging possible
• Unblocks any tool that requires terminal interaction
• Sessions persist - can work across multiple windows and tasks
• No need to build custom PTY management - tmux handles it all

Session Lifecycle Management

Default workflow:

1. List existing sessions to see what's available
2. Connect to existing session OR create new one
3. Create windows for your work
4. Do your work
5. Detach when done (session stays alive)

Never kill sessions unless:

• You created it in this conversation, AND
• User explicitly said "kill the session" or "destroy the session"

When user says "I'm done" or "clean up":

• Detach from the session
• Inform user the session is still running
• DO NOT kill it