//copies one file to another  #include<fcntl.h>#include<sys/stat.h>#define BUFSIZE 1024 #include<stdlib.h>int main(int argc ,char **argv){   int fd1,fd2;   int n,j;   char buf[BUFSIZE];   fd1=open(argv[1],O_RDONLY);   for(j=argc;j>1;j--)   {fd2=open(argv[j-1],O_WRONLY|O_CREAT|O_TRUNC|S_IRUSR|S_IWUSR|S_IROTH);   while((n=read(fd1,buf,BUFSIZE))>0)           write(fd2,buf,n);    close(fd2);   }  close(fd1);    exit(0);}