          close fileId
               Closes  the  file  given by fileId.  FileId must be the
               return value from a previous  invocation  of  the  open
               command;  after  this  command,  it  should not be used
               anymore.   If  fileId  refers  to  a  command  pipeline
               instead of a file, then close waits for the children to
               complete.  The normal result  of  this  command  is  an
               empty  string,  but  errors  are  returned if there are
               problems in closing the file or waiting for children to
               complete.
