forwarding a lua code to another

I have lua code which I called from another lua file and wants to assign a value and to print out the value but I am getting "nil", could you please help me. here is the code:

function main_setup()

  package.path = package.path ..";C:/Users/kude/Desktop/mqtt1/?.lua"              

  require "ds18b20"

end

local a = main_setup()

print(a)

output:

nil