preinst is in hfsutils-tcltk 3.2.6-12ubuntu3.
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 | #!/bin/sh
set -e
# dpkg can't handle replacing a directory with a symlink.
if [ "$1" = upgrade ] && dpkg --compare-versions "$2" lt-nl 3.2.6-8; then
rm -rf /usr/share/doc/hfsutils-tcltk
fi
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