IPV6 address validation using shell script

Question

I am using below script to validate IPV6 address but this script also pass invalid IP such as empty string, name etc.

if [[ "$IPv6ADDR"=~"^:?([a-fA-F0-9]{1,4}(:|.)?){0,8}(:|::)?([a-fA-F0-9]{1,4}(:|.)?){0,8}$" ]]; then
  echo "valid ipv6 addr"
  break;
else
  echo "Invalid IP Address"
  break;
fi

Can someone identify what's wrong in the regex, Please?

Answer 1

In your regex a blank string is allowed, as your pattern allows a string to not match any of the optional parts so its passing empty string.

Let me put my thoughts here -

My choice would be Python with using inet_pton

#!/usr/bin/env python
import socket
import sys
try:
    socket.inet_pton(socket.AF_INET6, sys.argv[1])
    result=0
except socket.error:
    result=1
sys.exit(result)

If you want to use shell script then try the following found on net not tested. (src: http://twobit.us/2011/07/validating-ip-addresses/ )

#!/bin/sh
WORD="[0-9A-Fa-f]\{1,4\}"
# flat address, no compressed words
FLAT="^${WORD}\(:${WORD}\)\{7\}$"
# ::'s compressions excluding beginning and end edge cases
COMP2="^\(${WORD}:\)\{1,1\}\(:${WORD}\)\{1,6\}$"
COMP3="^\(${WORD}:\)\{1,2\}\(:${WORD}\)\{1,5\}$"
COMP4="^\(${WORD}:\)\{1,3\}\(:${WORD}\)\{1,4\}$"
COMP5="^\(${WORD}:\)\{1,4\}\(:${WORD}\)\{1,3\}$"
COMP6="^\(${WORD}:\)\{1,5\}\(:${WORD}\)\{1,2\}$"
COMP7="^\(${WORD}:\)\{1,6\}\(:${WORD}\)\{1,1\}$"
# trailing :: edge case, includes case of only :: (all 0's)
EDGE_TAIL="^\(\(${WORD}:\)\{1,7\}\|:\):$"
# leading :: edge case
EDGE_LEAD="^:\(:${WORD}\)\{1,7\}$"
is_ipv6 () {
    echo $1 | grep --silent "\(${FLAT}\)\|\(${COMP2}\)\|\(${COMP3}\)\|\(${COMP4}\)\|\(${COMP5}\)\|\(${COMP6}\)\|\(${COMP7}\)\|\(${EDGE_TAIL}\)\|\(${EDGE_LEAD}\)"
    if [ $? -eq 0 ]; then
        return 1
    fi
    return 0
}

is_ipv6 $1
if [ $? -eq 1 ]; then
    exit 0
else
    echo "Invalid IPv6 address: $1" >&2
    exit 1
fi

Comments

Thanks Salil for the valuable info.