Linux Fish system update function

update.fish

function update
    if [ "$(which apt-get 2>/dev/null)" != '' ]
        sudo apt update -y
        sudo apt upgrade -y
        sudo apt autoremove -y
    else if [ "$(which dnf 2>/dev/null)" != '' ]
        sudo dnf update -y
    end
    if [ "$(which snap 2>/dev/null)" != '' ]
        sudo snap refresh
    end
    if [ "$(which flatpak 2>/dev/null)" != '' ]
        sudo flatpak update -y
    end
end