How to purge previously only removed packages? [duplicate]

I have a list of packages on my system, that were installed and removed again, but not purged, i.e. there are still a lot of conffiles etc. laying around.

The output of dpkg --get-selections | grep deinstall lists about 85 different packages which I don't need and want to be purged entirely.

So my short question, which I decided to finally ask after experimenting around has lead to this problem, is:

How do I completely purge previously installed packages that are already removed?

Reinstalling and then purging is not an option, of course.

I just found the following command which worked:

sudo apt-get purge $(dpkg -l | grep '^rc' | awk '{print $2}')

dpkg --get-selections | grep deinstall produces a list of package names with the word "deinstall":

$ dpkg  --get-selections | grep deinstall
account-plugin-windows-live         deinstall
debarchiver                         deinstall
flashplugin-installer               deinstall
    ...

By asking awk to print only the first field we get:

$ dpkg --get-selections | awk '$2 == "deinstall" {print $1}'
account-plugin-windows-live
debarchiver
flashplugin-installer
    ...

Now that we have the list of packages, xargs will let us feed the list of packages to a command (or commands, if the list is long enough):

dpkg --get-selections | awk '$2 == "deinstall" {print $1}' | xargs sudo apt-get purge --dry-run

When you are happy with the simulated results, replace --dry-run with -y in the apt-get command.

Relevant documentation:

man dpkg awk xargs apt-get

If you just want to purge the whole list, you can use this command; it will perform a dry run, in case essential packages are going to be removed, which you probably don't want to happen:

dpkg --get-selections | sed -n 's/\tdeinstall$//p' | xargs sudo apt-get --dry-run purge

If no essential package is going to be removed, it's safe to run the actual command:

dpkg --get-selections | sed -n 's/\tdeinstall$//p' | xargs sudo apt-get --yes purge

• sed -n 's/\tdeinstall$//p': prints only lines in stdin where a tabulation followed by a deinstall string could be removed from the end of the line; this has the effect of printing only the lines containing a tabulation followed by a deinstall string at the end of the line without the actual tabulation followed by the deinstall string at the end of the line
• xargs sudo apt-get --yes purge: passes each line in stdin as an argument to sudo apt-get --yes purge

My fifty cents, a simple oneliner:

First test with

dpkg --get-selections | awk '$2=="deinstall" {system("sudo apt-get --dry-run purge "$1)}'

and bye bye

dpkg --get-selections | awk '$2=="deinstall" {system("sudo apt-get -y purge "$1)}'

Example

% dpkg --get-selections | grep deinstall
nginx-common                    deinstall

% dpkg --get-selections | awk '$2=="deinstall" {system("sudo apt-get -y purge "$1)}'

% dpkg --get-selections | grep deinstall
[no output]

I asked this myself a couple of days ago. Came up with

apt-get purge $(dpkg -l | awk 'BEGIN{ORS=" "} /^rc/{ print $2}')

The removed but not purged packages appear in the output of dpkg -l with rc at the beginning. awk picks out the second column aka the name of the package and prints them space-separated.