当我们在linux系统中要删除数万或者数十万甚至数百万的文件时使用rm -rf *就不太好用，因为要等待很长一段时间。在这种情况之下我们可以使用linux系统命令rsync来巧妙的处理。rsync实际上用的是替换原理，处理数十万个文件也是秒删。
1. rsync安装，有些系统默认安装有该命令
Ubuntu系统：sudo apt-get install rsync
Fedora 系统：sudo yum install rsync
其他的可以源码安装，到下面的网站下载
2. rsync提供了一些跟删除有关的参数
rsync --help | grep delete
--delan alias for --delete-during
--delete delete extraneous files from destination dirs
--delete-beforereceiver deletes before transfer, not during
--delete-duringreceiver deletes during transfer (default)
--delete-delay find deletions during, delete after
--delete-after receiver deletes after transfer, not during
--delete-excluded also delete excluded files from destination dirs<
