postrm is in wireshark-common 1.10.6-1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | #!/bin/sh
set -e
GROUP=wireshark
if [ "$1" = "purge" ] ; then
      if getent group $GROUP >/dev/null; then
                if [ -x /usr/sbin/delgroup ]; then
                        echo "Removing wireshark group..."
                        delgroup --system $GROUP || echo "Could not remove wireshark group."
                fi
        fi
fi
# Automatically added by dh_installdebconf
if [ "$1" = purge ] && [ -e /usr/share/debconf/confmodule ]; then
	. /usr/share/debconf/confmodule
	db_purge
fi
# End automatically added section
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