slackbuilds/network/ddclient/doinst.sh

#!/bin/sh

config() {
  NEW="$1"
  OLD="$(dirname $NEW)/$(basename $NEW .new)"
  # If there's no config file by that name, mv it over:
  if [ ! -r $OLD ]; then
    mv $NEW $OLD
  elif [ "$(cat $OLD | md5sum)" = "$(cat $NEW | md5sum)" ]; then # toss the redundant copy
    rm $NEW
  fi
  # Otherwise, we leave the .new copy for the admin to consider...
}

preserve_perms() {
  NEW="$1"
  OLD="$(dirname $NEW)/$(basename $NEW .new)"
  if [ -e $OLD ]; then
    cp -a $OLD ${NEW}.incoming
    cat $NEW > ${NEW}.incoming
    mv ${NEW}.incoming $NEW
  fi
  config $NEW
}

preserve_perms etc/rc.d/rc.ddclient.new

# Keep same perms on ddclient.conf.new:
#   Normally, we don't bother with this for config files, but this one
#   should usually be readable only by root, so that's how we'll install
#   it.  However, if the admin changes it, we don't want to undo that.
preserve_perms etc/ddclient/ddclient.conf.new