I use this in my .bashrc to update my shell environment from tmux

tmup.sh

tmup () { 
    echo -n "Updating to latest tmux environment...";

    local IFS=",";
    for line in $(tmux showenv -t $(tmux display -p "#S") | tr "\n" ",");
    do
        if [[ $line == -* ]]; then
            unset $(echo $line | cut -c2-);
        else
            export $line;
        fi;
    done;
    echo "Done"
}