function split(str,sep)
  local tab = {}
  local find,send = string.find(str.."",sep)
  while find do
    print(str.."/"..find.."/"..send)
    table.insert(tab,string.sub(0,find-1))
    str = string.sub(str,find+1)
    find,send = string.find(str.."",sep)
  end
end

split("3:5:5",":")