postrm is in fontconfig 2.11.94-0ubuntu1.
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 | #! /bin/sh
set -e
case "$1" in
purge)
rm -f /var/log/fontconfig.log
rm -rf /var/cache/fontconfig
;;
esac
|