c15-1 -simple test of pipe

#include "apue.h"
int
main(void)
{
    int n;
    int fd[2];
    pid_t pid;
    char line[MAXLINE];

    if (pipe(fd) < 0)
        err_sys("pile error");
    if (( pid = fork() ) < 0)
    {
        err_sys("fokr error");
    } else if ( pid > 0) {
        close(fd[0]) ; /* parent close read pile */
        write(fd[1],"hello world",12);
    } else {
        close(fd[1]); /* child read write pile */
        n=read(fd[0],line,MAXLINE);
        write(STDOUT_FILENO,line,n);
    }
    exit(0);
}

   gcc  -Wall -o c15-1 c15-1.c error.c
./c15-1 
ubuntu@ubuntu-virtual-machine:~/Desktop/apue$ hello world

父进程关闭读端，子进程关闭写端，然后将父进程的输出写入子进程的输入，然后进行打印。