Here are some aptitude commands I use regularly but not often enough to remember each time…

List of manually installed packages. Usefull to clone an installation:

aptitude search -F%p ~i\!~M

• -F set a format string.
• %p is replaced by the package name.
• ~i select all installed packages.
• !~M excludes automaticaly installed packages.

With actually installed versions (usefull if some packages comes from backports or external repositories:

aptitude search --disable-columns -F%p=%v ~i\!~M

• --disable-columns unset displaying in columns and taking all terminal width.
• %v replaced by the version of the package.

Example: to clone a host (after copying all sources.list files):

aptitude install $(ssh machine_modele aptitude search --disable-columns -F%p=%v ~i\!~M |tr '\n' ' ')

Find updates available in backports or experimental:

aptitude versions '~W(~Awheezy-backports(~W(~i!~M)))'
aptitude versions '~W(~Aexperimental(~W(~i!~M)))'

• ~W ignores the version selected by another filter.
• ~Axxx select packages from archive xxx.

Lists upgradable packages:

aptitude search ~U

With version numbers:

aptitude search --disable-columns -F'%p     %v      %V' ~U

Lists modified configuration files:

sudo debsums -ce

Backup debconf configurations:

sudo debconf-get-selections > /tmp/conf-paquets.txt

To import as this befor installing packages:

sudo debconf-set-selections < /tmp/conf-paquets.txt

To be continued…