if tmux session "abc" exists {
    if tmux window "123" exists {
        attach tmux session "abc" window "123"
    } else {
        create tmux window "123" in tmux session "abc"
    }
} else {
  create tmux session "abc"
  create tmux window "123" in tmux session "abc"
  attach tmux session "abc" window "123"
}