Upgrade Brew if on OS X or apt-get otherwise. If parameter is received, upgrade a remote (Ubuntu) machine

upgrade.sh

if [ -z $1 ]
then
    if [ "$OS" == "Darwin" ]
    then
        echo "Updating…"
        brew update
        echo "Upgrading…"
        brew upgrade
    else
        sudo apt-get update
        sudo apt-get -u upgrade
    fi
else
    ssh $1 -t sudo apt-get update
    local dummy
    ssh $1 -t sudo apt-get --no-act upgrade
    echo -n "Process the upgrade ?"
    read -q dummy
    if [[ $dummy = "y" ]]
    then
        ssh $1 -t sudo apt-get -u upgrade --yes
    fi
fi