Ruby：如何将文件拆分为给定大小的多个文件

I want to split a txt file into multiple files where each file contains no more than 5Mb. I know there are tools for this, but I need this for a project and want to do it in Ruby. Also, I prefer to do this with File.open in block context if possible, but I fail miserably :o(I want to split a txt file into multiple files