Convert IPv6 from the compressed/short format to expanded format

Question

When I execute the command ip address show my server shows hundreds of IPv6 that I have assigned to it. It works great, however the leading and trailing zeros are omitted from the IP addresses, and are shown like:

3600:3c00:e000:92b::5/64 

I need the IP to get shown in the complete form like:

3600:3c00:e000:092b:0000:0005/64

because later I will match the result of ip address show into a regex to check for addresses from a list and all of them are in the "complete form".

Do you have any idea how I can fix this?

Answer 1

the following bash script will print IPv6 in expanded and in /proc/net/tcp6 format too (you can remove the last echo if you don't need it):

#!/bin/bash

# helper to convert hex to dec (portable version)
hex2dec(){
  [ "$1" != "" ] && printf "%d" "$(( 0x$1 ))"
}

# expand an ipv6 address
expand_ipv6() {
  ip=$1

  # prepend 0 if we start with :
  echo $ip | grep -qs "^:" && ip="0${ip}"

  # expand ::
  if echo $ip | grep -qs "::"; then
    colons=$(echo $ip | sed 's/[^:]//g')
    missing=$(echo ":::::::::" | sed "s/$colons//")
    expanded=$(echo $missing | sed 's/:/:0/g')
    ip=$(echo $ip | sed "s/::/$expanded/")
  fi

  blocks=$(echo $ip | grep -o "[0-9a-f]\+")
  set $blocks

  printf "%04x:%04x:%04x:%04x:%04x:%04x:%04x:%04x\n" \
    $(hex2dec $1) \
    $(hex2dec $2) \
    $(hex2dec $3) \
    $(hex2dec $4) \
    $(hex2dec $5) \
    $(hex2dec $6) \
    $(hex2dec $7) \
    $(hex2dec $8)
}

# print ipv6 in linux /proc/net/tcp6 format
ipv6ToNetTcp6() {
  ip=$1

  # prepend 0 if we start with :
  echo $ip | grep -qs "^:" && ip="0${ip}"

  # expand ::
  if echo $ip | grep -qs "::"; then
    colons=$(echo $ip | sed 's/[^:]//g')
    missing=$(echo ":::::::::" | sed "s/$colons//")
    expanded=$(echo $missing | sed 's/:/:0/g')
    ip=$(echo $ip | sed "s/::/$expanded/")
  fi

  blocks=$(echo $ip | grep -o "[0-9a-f]\+")
  set $blocks

  word1="0x$1"
  word2="0x$2"
  word3="0x$3"
  word4="0x$4"
  word5="0x$5"
  word6="0x$6"
  word7="0x$7"
  word8="0x$8"
  printf "%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X\n" \
    $((word2 & 0xFF)) \
    $((word2 >> 8)) \
    $((word1 & 0xFF)) \
    $((word1 >> 8)) \
    $((word4 & 0xFF)) \
    $((word4 >> 8)) \
    $((word3 & 0xFF)) \
    $((word3 >> 8)) \
    $((word6 & 0xFF)) \
    $((word6 >> 8)) \
    $((word5 & 0xFF)) \
    $((word5 >> 8)) \
    $((word8 & 0xFF)) \
    $((word8 >> 8)) \
    $((word7 & 0xFF)) \
    $((word7 >> 8))
}

result=$(expand_ipv6 $1)
echo $result
result2=$(ipv6ToNetTcp6 $1)
echo $result2

exit 0

E.g., after giving it execution permission:

# ./fullip6 "3600:3c00:e000:92b::5/64"
3600:3c00:e000:092b:0000:0000:0000:0005
003C00362B0900E00000000005000000