AVM's DHCP-server gibt alte WiFi-clients nicht frei

#!/bin/sh

# A script to get rid of unused leases that clog your AVM Fritzbox when used as a semi-public WiFi
# It is intended to run as a weekly cronjob.
# Something like this
#
# 47 4    * * 7   root    /sbin/tidy_ar7 && reboot
#

[ -e /var/flash/ar7.cfg ] || exit 1

# Use the arp table to get the currently connected clients
arp | egrep -o '([[:xdigit:]]{2}[:-]){5}[[:xdigit:]]{2}' >/tmp/arplist

LEASES=`grep -c ':' /var/flash/multid.leases`
LAME_LEASES=$(( ${LEASES} - `grep -c ':' /tmp/arplist` ))

if ! egrep -q '^ +landevices \{' /var/flash/ar7.cfg ; then
  echo "/var/flash/ar7.cfg has been changed by AVM and this script is now unable to work properly" >&2
  exit 1
fi

if [ ${LAME_LEASES} -lt 10 ] ; then
  echo "There are only ${LAME_LEASES} lame leases, I will make no change" >&2
  exit 1
fi

# use /var/flash/ar7.cfg to create 3 pieces
egrep -B9999 '^ +landevices \{' /var/flash/ar7.cfg                          >/tmp/ar7.first
egrep -A9999 '^ +landevices \{' /var/flash/ar7.cfg | egrep -B9999 -m1 '^}'  >/tmp/ar7.cfg.leases
egrep -A9999 '^ +landevices \{' /var/flash/ar7.cfg | egrep -A9999     '^}'  >/tmp/ar7.last

# Initialize
echo -n '' >/tmp/ar7.middle1
echo -n '' >/tmp/lease
KEEP=
IFS=''

# Parse the leases
while read line ; do
  # We reached the end... exit the loop
  echo "${line}" | egrep -q '^}$' && break

  # Determine if we keep the entry
  echo "${line}" | grep -qif /tmp/arplist  && KEEP=1
  echo "${line}" | grep -qi 'yes'          && KEEP=1
  echo "${line}" | grep -qi 'forwardrules' && KEEP=1
  echo "${line}" | grep -qi ' name ='      && KEEP=1

  # write one line of that section
  echo "${line}" >>/tmp/lease

  if echo "${line}" | egrep -q '}' ; then
    [ ${KEEP} ] && cat /tmp/lease >>/tmp/ar7.middle1
    KEEP=
    echo -n '' >/tmp/lease
  fi

done </tmp/ar7.cfg.leases

# sanity check: last line needs to contain a closing bracket....  otherwise abort
tail -n1 /tmp/ar7.middle1 | egrep -q '^ +}' || exit 1

# last line has either a closing and opening bracket or only a closing bracket
# replace last line with a line with only a closing bracket
head -n-2 /tmp/ar7.middle1  >/tmp/ar7.middle2
echo -e '        }'        >>/tmp/ar7.middle2

# create the new ar7.cfg by sticking the 2 ends to it
cat /tmp/ar7.first    >/tmp/ar7.cfg.new
cat /tmp/ar7.middle2 >>/tmp/ar7.cfg.new
cat /tmp/ar7.last    >>/tmp/ar7.cfg.new

# reminder we really eeed some more sanity checks here....
#
#

# let's do it
# stop the multi-daemon, empty its list and overwrite /var/flash/ar7.cfg
# Then exit with errorlevel 0

# Stop the 2 services involved
# /usr/bin/ctlmgr -s
/etc/init.d/rc.multid stop

# replace ar7.cfg with the modified one
cat /tmp/ar7.cfg.new >/var/flash/ar7.cfg
# replace multid.leases
grep  -if /tmp/arplist /var/flash/multid.leases >/tmp/multid.leases
cat /tmp/multid.leases >/var/flash/multid.leases

# Start the 2 services involved
# /usr/bin/ctlmgr
# /etc/init.d/rc.multid start

# clean the room after playing
rm /tmp/multid.leases
rm /tmp/ar7.first
rm /tmp/ar7.middle1
rm /tmp/ar7.middle2
rm /tmp/ar7.last
rm /tmp/lease
rm /tmp/arplist

exit 0