#!/bin/bash
regex='\[assembly: AssemblyVersion\("([^()]*)"\)\]'
fileContent="foo [assembly: AssemblyVersion(\"1.2.3\")] bar\")] quux"
[[ "$fileContent" =~ $regex ]]
echo "${BASH_REMATCH[1]}"
IyEvYmluL2Jhc2gKcmVnZXg9J1xbYXNzZW1ibHk6IEFzc2VtYmx5VmVyc2lvblwoIihbXigpXSopIlwpXF0nCmZpbGVDb250ZW50PSJmb28gW2Fzc2VtYmx5OiBBc3NlbWJseVZlcnNpb24oXCIxLjIuM1wiKV0gYmFyXCIpXSBxdXV4IgpbWyAiJGZpbGVDb250ZW50IiA9fiAkcmVnZXggXV0KZWNobyAiJHtCQVNIX1JFTUFUQ0hbMV19Ig==