Most programs are looking for files they need (like config files, GUI ressources, ...) on a few hardcoded places and will refuse to works if those files aren't there. To change this places you usually need to recompile the programs (but sometimes you can use command line options or environment variables instead).
dpkg and apt offer a way to change the install location (as far as I remember it's --root= with dpkg and Dir::Root in the apt config - but check the docs if you really need it). This is so you can mount another systems's root dir on your system and install packages on it (like if you have diskless systems mounting their root via NFS from a server).
According to the documentation you can add a config file to /etc/apt/apt.conf.d/ named no-cache containing Dir::Cache ""; and Dir::Cache::archives ""; according to manual of apt.conf. There is a bug report raising issues with this method, and I don't recommend it.
There is one remaining method according to this tutorial:
Best Answer
The
apt-getcommand closer toaptitude safe-upgradeisupgrade, but there is a difference.aptitude safe-upgradeupgrades currently installed packages and can install new packages to resolve new dependencies, but never removes packages.apt-get upgradeupgrades currently installed packages, but never installs or removes packages.So
apt-get upgradeis comparable toaptitude --no-new-installs safe-upgrade.