Myshellv0.3

代码说明：

  在myshell v0.1的基础上，增加新的功能：在父进程中接收控制台输入一行字符串，作为用户发出的Linux命令，如ls /usr/*.c ，在创建一个子进程后，子进程通过调用execlp()系统调用，执行这条命令。(In the myshell v0.1 based on adding new features: In the parent process to receive the console input line of string, as issued by the Linux user commands, such as ls/usr /*. c < Enter " , in creating a sub- the process, the child process by calling execlp () system call, the implementation of this Order.)