Bash script for i3 to run terminal in the same working directory as active window running tmux

i3-shell.sh

#!/bin/bash
# i3 thread: https://faq.i3wm.org/question/150/how-to-launch-a-terminal-from-here/?answer=152#post-id-152
# based on https://gist.github.com/viking/5851049 and https://gist.github.com/TiddoLangerak/c61e1e48df91192f9554

CWD=''
CMD='/usr/bin/x-terminal-emulator'

# Get window ID
ID=$(xdpyinfo | grep focus | cut -f4 -d " ")

# Get PID of process whose window this is
PID=$(xprop -id $ID | grep -m 1 PID | cut -d " " -f 3)

# Get first child process (shell, vim, etc)
if [ -n "$PID" ]; then
	TREE=$(pstree -lpA $PID | head -n 1)
	PROCESS=$(echo $TREE | awk -F'---' '{print $NF}')
	if [[ $PROCESS == tmux* ]];
	then
		PID=$(tmux list-panes -F '#{pane_active} #{pane_pid}' | cut -d " " -f 2)
	fi

	# If we find the working directory, run the command in that directory
	if [ -e "/proc/$PID/cwd" ]; then
		CWD=$(readlink /proc/$PID/cwd)
	fi
fi

if [ -n "$CWD" ]; then
    cd $CWD && $CMD
  else
    $CMD
fi