#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#define BUFERSIZE 4096
#define COPYMODE 0644

void oops(char *, char *);
int main (int ac, char *av[])
{
           int in_fd, out_fd, n_chars;
          char buf[BUFERSIZE];
       if (ac != 3) {
                fprintf(stderr, "usage: %s source destination\n", *av);
                exit(1);
         {
        if ((in_fd = open(av[1], O_RDONLY)) == -1)
                [br]oops("Cannot open", av[1]);
        if ((out_fd = creat(av[2], COPYMODE)) == -1)
                oops("Cannot creat", av[2]);
        while ((n_chars = read(in_fd, buf, BUFERSIZE)) > 0)
                if (write(out_fd, buf, n_chars) != n_chars)
                        oops("Write error to", av[2]);
        if (n_chars == -1)
                oops("Read error from", av[1]);
        if (close(in_fd) == -1 || close(out_fd) == -1)
                oops("Error closing files", " ");

        void oops (char *s1, char *s2)
        {
                fprintf(stderr, "Error: %s", s1);
                perror(s2);
                exit(1);
        }
}