copyfile.c

#include <sys/types.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>

#define BUF_SIZE 4096
#define OUTPUT_MODE 0700
#define TRUE 1


int main(int argc, char *argv[]);

int main(int argc, char *argv[]) {

    int in_fd, out_fd, rd_count, wt_count;
    char buffer[BUF_SIZE];

    if (argc != 3) exit(1);

    in_fd = open(argv[1], O_RDONLY);
    if (in_fd < 0) exit(2);

    out_fd = creat(argv[2], OUTPUT_MODE);
    if (out_fd < 0) exit(3);

    while (TRUE) {
        rd_count = read(in_fd, buffer, BUF_SIZE);
        if (rd_count <= 0) break;

        wt_count = write(out_fd, buffer, rd_count);
        if (wt_count <= 0) exit(4);
    }

    close(in_fd);
    close(out_fd);
    if (rd_count == 0) {
        exit(0);
    } else {
        exit(5);
    }
}