preinst is in libxml2-dev 2.9.1+dfsg1-3ubuntu4.
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 | #!/bin/sh
set -e
[ "$1" = "upgrade" ] &&
[ -L /usr/share/doc/libxml2-dev ] &&
rm -f /usr/share/doc/libxml2-dev
exit 0
|