管道与重定向
http://www.cnblogs.com/chengmo/archive/2010/10/20/1855805.html
http://www.cnblogs.com/chengmo/archive/2010/10/21/1856577.html
http://www.cnblogs.com/chengmo/archive/2010/10/20/1855805.html
http://www.cnblogs.com/chengmo/archive/2010/10/21/1856577.html