dup2

int dup2(int oldfd,newfd);

use

duplicate the file descritpor oldfd to newfd

return code

return the copy of the file descriptor on sucess or return -1 and set errno on error

• EBADF
oldfd is not open or don’t exist
• EBADF
newfd is aready open or don’t exist
• EIO
  an IO error happend while duplicating fd