// 写一段附加到进程的主程序
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
    int fd;
    char buf[1024];
    int n;
    if (argc != 2)
    {
        printf("Usage:%s <file>\n", argv[0]);
        exit(1);
    }
    fd = open(argv[1], O_RDWR);
    if (fd < 0)
    {
        perror("open");
        exit(1);
    }
    while (1)
    {
        n = read(fd, buf, sizeof(buf));
        if (n == 0)
        {
            break;
        }
        write(STDOUT_FILENO, buf, n);
    }
    close(fd);
    return 0;
}