Duplicating subsets of package selections between systems

I'm building a pair of Ubuntu systems for kids. For a variety of reasons, including lack of time and hardware problems, this has taken far longer than expected and I ended up with one running 9.10 (Karmic Koala) and the other 10.04 (Lucid Lynx). Since the Karmic system has the most testing effort into it (reviewing games for stability and kid appropriateness) I needed a way to duplicate the selection of games on the Lucid system while filtering out everything else since some packages are release-specific.

Using Synaptic it is possible to export (File > Save Markings) either a list of packages that have changed selection state but the changes haven't been applied yet or optionally a list of all packages and their status. While Synaptic can filter displayed packages by repository or type (the "section" parameter in the deb INFO file), these have no effect on the markings export.

The apt-get command (or dpkg directly) can be used to create a full list of packages but to produce a filtered list you need to use aptitude.

Aptitude has a search function that can be used to filter based on almost anything in a deb package INFO file. For example, to get a list of games available and save it to a game_selections.txt file:

aptitude search '?section(games)' >game_selections.txt

The question marks in the search pattern indicate that a search term follows. Because the parenthesis are special characters to the shell they need to have quotes around them. In this example "section" indicates the section parameter and "games" is term that is being searched for. Any package with a section parameter set to "games" will be listed:

...
i chromium-bsu - fast paced, arcade-style, scrolling space
i A chromium-bsu-data - data pack for the Chromium B.S.U. game
p chromium-data - transitional dummy package for chromium-bs
p circuslinux - The clowns are trying to pop balloons to score points!
p circuslinux-data - data files for circuslinux
...

The leading character indicates it's state with "i" for installed, "i A" for automatically installed (either recommended or a dependency), and "p" for purged (i.e. no trace of existence on system which is the default state of all packages). To filter for installed packages only you add the "?install" parameter:

aptitude search '?section(games) ?installed' >game_selections.txt

...
i chromium-bsu - fast paced, arcade-style, scrolling space shooter
i A chromium-bsu-data - data pack for the Chromium B.S.U. game
i glchess - Chess strategy game
i glines - Five or More puzzle game
i gnect - Four in a Row strategy game
i gnibbles - Worm arcade game
i gnobots2 - Avoid robots game
i gnome-blackjack - Blackjack casino card game
...

The status and descriptions will cause syntax errors when using the file as input to aptitude so a format needs to be specified to filter them out. The "-F" parameter is used to indicate a format change and "%p" equates to the package name:

aptitude search -F '%p' '?section(games) ?installed' >game_selections.txt

...
chromium-bsu
chromium-bsu-data
glchess
glines
gnect
gnibbles
gnobots2
gnome-blackjack
...

To use game_selections.txt as input to aptitude on another system just use command substitution (see the sh or bash man page) to redirect it from the shell:

aptitude install $(< game_selections.txt)

On Ubuntu you need to use sudo in front of this command or use "sudo su" to create a root shell and issue it from there.