/*this file work for test the pipe write*/#include <unistd.h>#include <sys/types.h>main(){	int pipe_fd[2];	pid_t pid;	char r_buf[4];	char* w_buf;	int writenum;	int cmd;		memset(r_buf,0,sizeof(r_buf));	if(pipe(pipe_fd)<0)	{		printf("pipe create error\n");		return -1;	}		if((pid=fork())==0)	{		close(pipe_fd[0]);		close(pipe_fd[1]);		sleep(10);			exit();	}	else if(pid>0)	{	sleep(1);  //等待子進程完成關閉讀端的操作	close(pipe_fd[0]);//write	w_buf="111";	if((writenum=write(pipe_fd[1],w_buf,4))==-1)		printf("write to pipe error\n");	else			printf("the bytes write to pipe is %d \n", writenum);		close(pipe_fd[1]);	}	}