          seek fileId offset ?origin?
               Change  the  current  access  position for fileId.  The
               offset and origin arguments  specify  the  position  at
               which  the  next  read  or write will occur for fileId.
               Offset must be a number (which  may  be  negative)  and
               origin must be one of the following:

               start
                    The  new access position will be origin bytes from
                    the start of the file.

               current
                    The  new access position will be origin bytes from
                    the current access  position;  a  negative  origin
                    moves the access position backwards in the file.

               end
                    The  new access position will be origin bytes from
                    the end of the file.  A negative origin places the
                    access  position  before  the  end-of-file,  and a
                    positive origin places the access  position  after
                    the end-of-file.

               The origin argument defaults  to  start.   FileId  must
               have  been  the  return  value  from a previous call to
               open, or it may be stdin, stdout, or stderr to refer to
               one of the standard I/O channels.  This command returns
               an empty string.
