linux下 写的myshell代码，可以cd功能，简单的命令支持管道，重定向-write myshell under linux code, cd function, a simple command to support pipes, redirection

自己编写的shell 解释器，包括myshell.c parse.lex he makefile三个文件可以实现列表，管道，重定向，内外部命令-I have written a shell interpreter, including three myshell.c parse.lex he makefile file list can be achieved, pipes, redirection, internal and external commands, etc.