A few times I have had the need to simulate the way tasksel installs packages during the normal debian-installer run. Until now, I have ended up letting tasksel do the work, with the annoying problem of not getting any feedback at all when something fails (like a conffile question from dpkg or a download that fails), using code like this:
This would invoke tasksel, let its automatic task selection pick the tasks to install, and continue to install the requested tasks without any output what so ever. Recently I revisited this problem while working on the automatic package upgrade testing, because tasksel would some times hang without any useful feedback, and I want to see what is going on when it happen. Then it occured to me, I can parse the output from tasksel when asked to run in test mode, and use that aptitude command line printed by tasksel then to simulate the tasksel run. I ended up using code like this:export DEBIAN_FRONTEND=noninteractive tasksel --new-install
export DEBIAN_FRONTEND=noninteractive cmd="$(in_target tasksel -t --new-install | sed 's/debconf-apt-progress -- //')" $cmd
The content of $cmd is typically something like "aptitude -q --without-recommends -o APT::Install-Recommends=no -y install ~t^desktop$ ~t^gnome-desktop$ ~t^laptop$ ~pstandard ~prequired ~pimportant", which will install the gnome desktop task, the laptop task and all packages with priority standard , required and important, just like tasksel would have done it during installation.
A better approach is probably to extend tasksel to be able to install packages without using debconf-apt-progress, for use cases like this.