Auto-detect virtualenv relatively from current directory

.bashrc

# auto source virtual envs if it can find one
has_virtualenv() {
    path="../env/bin/activate"
    if [ -e $path ]; then
        path=$(readlink -f $path)
        if [ -z "$CURRENT_VENV_PATH" -o -z "$_OLD_VIRTUAL_PATH" -o "$CURRENT_VENV_PATH" != "$path" ] ; then
            source $path
            export CURRENT_VENV_PATH="$path"
            echo -e "\e[01;30mvirtualenv $path activated\e[00m"
        fi
    fi
}
venv_cd () {
    cd "$@" && has_virtualenv
}
alias cd="venv_cd"