Need Help : 32 bit / 64 bit check for Linux

I need to write a bash script where i have to check whether Linux installation is 32 bit or 64 bit. How can i check the same.currently i am using the below command : uname -a command and gives me x86_64 result but i believe i can not use it in the generic way because result may differ if some one using non x86 architecture. Please help.