apk

You can look at the apt log under /var/log/apt/ and the dpkg log under /var/log/

and you can get the list of the installed packages with just a command:

dpkg -l | grep '^ii '

To list all installed packages,

dpkg -l |awk '/^[hi]i/{print $2}' > 1.txt
or
aptitude search -F '%p' '~i' > 1.txt
or
dpkg --get-selections > 1.txt

dpkg-query (instead of dpkg –get-selections, which lists some packages that are not installed) as follows:

dpkg-query -W -f='${PackageSpec} ${Status}\n' | grep installed |  sort -u | cut -f1 -d \ > installed-pkgs

Or:

$ dpkg -l | grep ^ii | sed 's_  _\t_g' | cut -f 2 > installed-pkgs

Create a backup of what packages are currently installed:

dpkg --get-selections > list.txt

Then (on another system) restore installations from that list:

dpkg --clear-selections
sudo dpkg --set-selections < list.txt

To get rid of stale packages

sudo apt-get autoremove

To get installed like at backup time (i.e. to install packages set by dpkg --set-selections)

sudo apt-get dselect-upgrade

To get just the packages which were expressly installed (not just installed as dependencies), you can run

aptitude search '~i!~M'

dpkg --get-selections | grep -v deinstall

dpkg --get-selections | grep postgres

dpkg --get-selections | grep -v deinstall > ~/Desktop/packages

dpkg -l

apt --installed list

sudo apt-get purge --auto-remove packagename

it will purge required packages along with dependencies that are installed with that packages. --auto-remove option work similar to sudo apt-get autoremove