close − delete a descriptor
The close call deletes a file descriptor and performs any device driver defined activity necessary when terminating access to the file.  A close of all of a standalone programs descriptors is automatic on but since there is a limit on the number of active descriptors per process, is necessary for programs that deal with many descriptors.  Upon successful completion, a value of 0 is returned.  Otherwise, a value of −1 is returned and the global integer variable is set to indicate the error.  will fail if: [EBADF] D is not an active descriptor.  open(3spp), read(3spp), write(3spp), ioctl(3spp), lseek(3spp)