cp.c

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

#define BUF_SIZE 8192

int main(int argc, char* argv[])
{
    int input_fd, output_fd;
    ssize_t ret_in, ret_out;
    char buffer[BUF_SIZE];

    if(argc != 3) {
        printf("Usage: cp file1 file2\n");
        return 1;
    }

    input_fd = open(argv[1], O_RDONLY);
    if(input_fd == -1) {
        perror("Open error\n");
        return 2;
    }

    output_fd = open(argv[2], O_WRONLY | O_CREAT, 0064);
    if(output_fd == -1) {
        perror("Open error\n");
        return 3;
    }

    while((ret_in = read(input_fd, &buffer, BUF_SIZE)) > 0) {
        ret_out = write(output_fd, &buffer, (ssize_t) ret_in);
            if(ret_out != ret_in) {
                perror("Write error\n");
                return 4;
            }
    }

    close(input_fd);
    close(output_fd);

    return 0;
}