preinst is in mythbuntu-control-centre 0.63-0ubuntu2.
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 22 | #! /bin/sh
set -e
# Automatically added by dh_pycentral
case "$1" in
    install|upgrade)
	mkdir -p /var/lib/pycentral
	echo '# the presence of this file allows calling pkgremove on upgrade' \
	    > /var/lib/pycentral/mythbuntu-control-centre.pkgremove
esac
# End automatically added section
case "$1" in
        upgrade)
        if dpkg-divert --list mythbuntu-control-centre | grep diverted >/dev/null; then
            dpkg-divert --package mythbuntu-control-centre --remove \
                    --rename --divert /usr/share/mythtv/main_settings.xml.diverted /usr/share/mythtv/main_settings.xml
        fi
        ;;
esac
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