preinst is in libcanberra-gtk3-module 0.30-5ubuntu1.
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 | #!/bin/sh
set -e
case "$1" in
upgrade)
if dpkg --compare-versions "$2" le "0.28-2"; then
if [ -f '/etc/X11/Xsession.d/52libcanberra-gtk3-module_add-to-gtk-modules/52libcanberra-gtk-module_add-to-gtk-modules' ]; then
rm -f '/etc/X11/Xsession.d/52libcanberra-gtk3-module_add-to-gtk-modules/52libcanberra-gtk-module_add-to-gtk-modules'
fi
fi
esac
exit 0
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