mywindow="test"
tmux -q has-session -t mysession || tmux new -s mysession -d
if tmux -q select-window -t mysession:$mywindow
then
    tmux -q attach -t mysession
else
    tmux -q new-window -t mysession -n $mywindow
    tmux -q send-keys -t mysession:$mywindow "mycommand" ENTER
fi