12.c

#include <stdio.h>

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <unistd.h>

#define BUFSIZE 1

int main(int argc, char *argv[])
{
    int src, des;
    char ch[BUFSIZE];
    int ret;

    if (argc < 3)
    {
        fprintf(stderr, "Usage: %s src des\n", argv[0]);
        return -1;
    }

    src = open(argv[1], O_RDONLY);
    if (src == -1)
    {
        perror("open read");
        return -1;
    }
    des = open(argv[2], O_WRONLY | O_TRUNC, 0777);
    if (des == -1)
    {
        perror("open des");
        return -1;
    }

    while (1)
    {
        ret = read(src, ch, BUFSIZE);
        if (ret == 0)
        {
            break;
        }
        write(des, ch, ret);
    }

    fsync(src);
    fsync(des);

    close(src);
    close(des);
}