tr

1. tr 详解 http://blog.sina.com.cn/s/blog_58c3f7960100uttl.html

                http://www.cnblogs.com/wangkangluo1/archive/2012/05/31/2528059.html

                http://blog.csdn.net/jeffreyst_zb/article/details/8047065

2. tr命令 http://man.linuxde.net/tr