This is a small utility to keep track of package changes in a Debian-based
system like Ubuntu, and of course Debian itself. 

A typical output from pkghist looks like this:

2013-03-06 (Wed)

       purged> 13:30  ecryptfs-utils ()
               12:37  ecryptfs-utils (68-1+lenny1)
               12:37  keyutils (1.2-9)
               12:37  libecryptfs0 (68-1+lenny1)
               12:37  libgpgme11 (1.1.6-2)
               12:37  libpth20 (2.0.7-12)
       purged> 12:36  mimms ()
    uninstall> 12:36  libmms0 (0.4-2)

2013-02-28 (Thu)

               23:36  mimms (3.2.1-1)
               23:36  libmms0 (0.4-2)

2013-01-30 (Wed)

      upgrade> 17:16  samba-common (2:3.2.5-4lenny15)
               17:16  smbfs (2:3.2.5-4lenny15)
      upgrade> 17:16  samba (2:3.2.5-4lenny15)
      upgrade> 17:16  smbclient (2:3.2.5-4lenny15)

...snipped...

While tools like dpkg-query tells you what is currently installed, it does
not tell you when it was installed, what has been upgraded, what was been
removed etc. It can be useful to know these information, especially if you
set the system to do unattended upgrades.

== Others ==

Ubuntu users already have something like:
less /var/log/apt/history.log

On other Debian systems:
less /var/log/dpkg.log

A quick google found other similar ones like this: 
http://linuxcommando.blogspot.com/2008/08/how-to-show-apt-log-history.html

I prefer something that is formatted for readability and works for not just
Ubuntu but any Debian-based systems. Plus something that keeps a complete
history, not just what is available in the log file.

== Description ==

pkghist is written in Perl and uses dpkg-query to get current package info,
and compares this to what was stored in a history file (default
/var/lib/dpkg/pkghist.log). By comparing the differences, we know what has
been installed, upgraded, purged etc.

pkghist needs to be run after packages has been changed, so one way to keep
it updated is to put it into cron:
30 * * * * /usr/bin/pkghist.pl -u

If you do not want to run as root, you need to specify an alternative
location for the history file like this:
30 * * * * /usr/bin/pkghist.pl -u -f ~/.pkghist.log

Another better way is to create a dpkg post-invoke hook (by creating say 80-updatepkghist in /etc/apt/apt.conf.d):
DPkg::Post-Invoke { "/usr/bin/pkghist.pl -u" };