Synopsis:
   $close(<file descriptor>)

Technical:
   This function unbinds the given file descriptor (previously returned by
   the $open() function) from the underlying file, causing the file to be
   committed to disk if necessary.  An error is returned if it is passed a
   file descriptor not produced by an $open() call.

Practical:
   This function is used to close a file that was opened for reading or
   writing by $open().  Data corruption may result if the client exits
   before all open files are closed.

Returns:
   -1   error
    0   file closed successfully

See Also:
   open(6); read(6); write(6)