Debian: find packages without reverse dependencies

When trying to make minimal OS, one wants to get rid of as many non-critical packages as possible. Under Debian, apt-cache rdepends --installed on a given package shows the reverse dependencies, or a list of other packages that depends on it.

The bash script below scans all installed packages and emits a list of packages without any reverse dependencies.

Packages without any reverse dependencies could be one of three things:

1. Orphans - truly not used by anything. apt-get purge away.
2. A top-level user command, something like wget
3. Something critical for booting. Interestingly, bash comes up without reverse dependencies, but it's hard to imagine Debian booting without it.

Enjoy!

#!/bin/bash

# provides list of packages that have
# nothing depending on them

for target in `dpkg -l | grep '^ii' | awk '{ print \$2 }'`; do
   if [ "`apt-cache rdepends --installed $target | wc -l`" = "2" ]; then
      echo "$target"
   fi
done