netdevs_we_want_to_rename="eth3 eth1 eth2 eth4"
netdevs_desired_names="lan1 lan2 lan3 lan4"
temp_names=""

i=0
for netdev in $netdevs_we_want_to_rename; do
  while [ -e "/sys/class/net/tmp$i" ]; do : $((i++)); done
  ip link set "$netdev" down
  ip link set "$netdev" name "tmp$i"
  temp_names="${temp_names:+$temp_names }tmp$i"
done

for netdev in $temp_names; do
  desired_name=${netdevs_desired_names%% *}
  netdevs_desired_names=${netdevs_desired_names#* }
  ip link set "$netdev" name "$desired_name"
  ip link set "$netdev" up
done