在Web服务器上设置共享php脚本文件的最佳方法是什么？

I'm running the same php script on many domains on an apache2 server. Only some of the files change between domains, and the rest are always the same. Right now, every time I set up a new domain, I copy all the files, but I'd really like to have these common files in one place so any changes would affect all domains.I'm running the same php script on many domains