Linux进程控制:父进程打开一个文件，然后创建两个子进程。子进程1将打开文件中的小写字母换成大写字母。子进程2将文件内容读出后打印。父进程等待两个子进程结束以后关闭文件，结束。

-Linux process control: a parent process opens a file, and then create two sub-processes. A child process will open the file in lowercase letters replaced by uppercase letters. Child 2 after printing the file contents read out. Parent process to wait to close the file after the end of the two sub-process, finished.