Force naming tmux session

.zshrc

if [ ! -z $TMUX ]; then
    tmux show-options | grep "TMUX_NO_FORCE_NAME_SESSION" > /dev/null
    if [ $? -ne 0 ]; then
        SESSION_NAME=`tmux display-message -p '#S'`
        echo $SESSION_NAME | grep "^[0-9]\+$" > /dev/null
        if [ $? -eq 0 ]; then   # Not named
            /bin/echo -n "tmux session name: "
            read NAME
            if [ ! -z $NAME ]; then
                tmux rename-session $NAME
            else
                tmux set-option update-environment TMUX_NO_FORCE_NAME_SESSION=1
            fi
        fi
    fi
fi