wget -nv https://download.opensuse.org/repositories/home:Alexx2000/xUbuntu_18.10/Release.key -O Release.key
sudo apt-key add - < Release.key
sudo apt-get update

sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/Alexx2000/xUbuntu_18.10/ /' > /etc/apt/sources.list.d/home:Alexx2000.list"
sudo apt-get update
sudo apt-get install doublecmd-gtk