postinst is in tidy 20091223cvs-1ubuntu2.
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 23 24 | #!/bin/sh -e
# Move a conffile without triggering a dpkg question
mv_conffile() {
    OLDCONFFILE="$1"
    NEWCONFFILE="$2"
    if [ -e "$OLDCONFFILE" ]; then
        echo "Preserving user changes to $NEWCONFFILE ..."
        mv -f "$NEWCONFFILE" "$NEWCONFFILE".dpkg-new
        mv -f "$OLDCONFFILE" "$NEWCONFFILE"
    fi
}
case "$1" in
configure)
    if dpkg --compare-versions "$2" le "$LASTVERSION"; then
        mv_conffile "/etc/tidy/tidy.conf" "/etc/tidy.conf"
    fi
esac
exit 0
 |