如何在Bash中检测tmux会话是否存在及是否已连接？

Your core requirement is to safely create a tmux session only if it doesn't exist, and attach to it only when you're not already inside a tmux session. Here's a clean, reliable approach that avoids parsing tmux ls output (which can be fragile) and uses tmux's built-in tools for better robustness.

Key Checks to Use #

Instead of grepping tmux ls, rely on these more reliable methods:

• Check if a session exists: Use tmux has-session -t <session-name> 2>/dev/null. This command exits with a status code of 0 if the session exists, and non-zero otherwise. Redirecting stderr to /dev/null suppresses the error message when the session isn't found.
• Check if you're already in tmux: Verify if the TMUX environment variable is set. If it's empty, you're outside a tmux session; if it's present, you're already attached to one.

Full Script Implementation #

Here's a complete script that meets all your requirements:

#!/bin/bash

# Define your session name
SESSION_NAME="ax"

# Step 1: Create the session only if it doesn't exist
if ! tmux has-session -t "$SESSION_NAME" 2>/dev/null; then
    # Create the initial session with a window named 'ui' (detached mode)
    tmux new-session -s "$SESSION_NAME" -n ui -d
    
    # Add additional windows here (only runs once when the session is first created)
    tmux new-window -t "$SESSION_NAME" -n backend
    tmux new-window -t "$SESSION_NAME" -n logs
    
    # Optional: Set the default window to 'ui' when attaching
    tmux select-window -t "$SESSION_NAME:ui"
fi

# Step 2: Attach to the session only if not already in tmux
if [ -z "$TMUX" ]; then
    tmux attach-session -t "$SESSION_NAME"
else
    echo "Already inside a tmux session. To switch to $SESSION_NAME, use: tmux switch-client -t $SESSION_NAME"
fi

How It Works #

• Session Creation: The if ! tmux has-session block ensures we only run the session setup (initial window + additional windows) once, when the session is first created. This prevents duplicate windows if the script is run multiple times.
• Attachment Logic: The [ -z "$TMUX" ] check ensures we only attach to the session if we're not already inside tmux. If we are in tmux, we print a helpful tip for switching sessions instead.

Extra Tips #

• Switching Sessions: If you're already in tmux and want to switch to your ax session, use tmux switch-client -t ax instead of attaching again.
• Idempotent Setup: All the commands inside the session creation block run only when the session doesn't exist — exactly what we want to avoid duplicate windows or sessions.
• Clean Output: Redirecting stderr in tmux has-session keeps the script quiet when the session doesn't exist, avoiding unnecessary error messages.

内容的提问来源于stack exchange，提问作者GibboK