dup,dup2,pipe

看完这几个链接基本的概念大概学会了。
http://www.xxlinux.com/linux/article/development/soft/20071214/13347.html
http://blog.csdn.net/mkowzy/archive/2007/08/12/1739789.aspx
http://blog.csdn.net/mkowzy/archive/2007/08/12/1739809.aspx
http://pdos.csail.mit.edu/6.828/2010/lec/l-overview.html