实验要求：在Myshell系列实验之二的基础上，增加下列功能：

　　1根据接收控制台命令，如包含’>’符号，则进行输出重定向到文件，如: ls /home/mydir > mylist.txt

　　2根据接收控制台命令，如包含’<’符号，则进行输入重定向到文件，如: sort < mylist.txt

　　3根据接收控制台命令，如包含’>’和’>’符号，则进行输入输出重定

　　-Experimental requirements: The second series of experiments in Myshell basis, add the following features: 1 under the receiver console commands, such as including ' > '　symbols, the output will be redirected to the file, such as: ls/home/mydir>　mylist.txt 2 of the receiving console commands, such as containing ' < '　" sign, then redirect to a file for input, such as: sort < mylist.txt 3 console, according to the received commands, such as including ' > '　and ' > '　symbol, then for input output-set