说明：  程序，创建一个管道PIPE，复制进程，父进程运行命令“ls -l”，把运行结果写入管道，子进程从管道中读取“ls -l”的结果，并结果输出到屏幕
(Program, create a pipeline the PIPE, the replication process, the parent process run the command "ls-l", write the results of running pipeline, the child process to read the "ls-l" results in the pipeline, and the resulting output to the screen)