Add multiple IPv6 address on prefix change.

add-multiple-ipv6.sh

#!/bin/bash

IPv6PrefixFile=$HOME/IPv6Prefix.txt
IPv6Prefix=$(cat $IPv6PrefixFile)

__rfc5952_expand () {
read addr mask < <(IFS=/; echo $1)
quads=$(grep -oE "[a-fA-F0-9]{1,4}" <<< ${addr/\/*} | wc -l)
grep -qs ":$" <<< $addr && { addr="${addr}0000"; (( quads++ )); }
grep -qs "^:" <<< $addr && { addr="0000${addr}"; (( quads++ )); }
[ $quads -lt 8 ] && addr=${addr/::/:$(for (( i=1; i<=$(( 8 - quads )) ; i++ )); do printf "0000:"; done)}
addr=$(for quad in $(IFS=:; echo ${addr}); do printf "${delim}%04x" "0x${quad}"; delim=":"; done)
[ ! -z $mask ] && echo $addr/$mask || echo $addr
}

IPv6Current=$(/sbin/ip -6 addr | grep inet6 | grep -vE 'host|mngtmpaddr|temporary' | grep -F 'scope global dynamic' | sed -e 's/^.*inet6 \([^ ]*\)\/.*$/\1/;t;d' | grep '^2')
IPv6Current="$(__rfc5952_expand $IPv6Current)"

IPv6Current=${IPv6Current:0:19}

if [ $IPv6Current != $IPv6Prefix ]; then

for i in $(cat $HOME/ipv6-addresses.txt);
do
	ip -6 addr del ${IPv6Prefix}:${i} dev ens18
	ip -6 addr add ${IPv6Current}:${i} dev ens18
done

echo $IPv6Current > $IPv6PrefixFile
fi

exit 0

First create a file using

echo "0000:0000:0000:0000" > $HOME/IPv6Prefix.txt

After that create another file for storing all the suffix.

ipv6-addresses.txt

For Example
5e37:080b:66b7:68bb
52bf:52fe:a1df:60e3
3b32:a9d4:a9f3:074f
9ec7:f4da:b166:0a5f
620c:eb97:3e93:ece3

Rebooting the server removes all the added IPv6 suffixes so on server startup reset the IPv6Prefix.txt file again using
echo "0000:0000:0000:0000" > $HOME/IPv6Prefix.txt
because on reboot the script thinks the prefix has not changed and will not add the suffix on a fresh boot.