14.6.5 Writing Records
  For a file opened with ACCESS WRITE or ACCESS
  MODIFY, the PUT statement moves data from the record
  buffer to a file using the I/O buffer. PUT statements are
  valid on RMS sequential, relative, and indexed files. You can-
  not use PUT statements on terminal-format files or virtual
  array files.

  Sequential access is valid on RMS sequential, relative, and
  indexed files. For sequential, variable, and stream files, a se-
  quential PUT operation adds a record at the end of the file.
  For sequential fixed and relative files, PUT writes records
  sequentially or randomly depending on the presence of a
  RECORD clause. For indexed files, RMS stores records in
  order of the primary key's collating sequence. Therefore,
  you do not need to specify a random or sequential PUT.
  Table 14-3 shows the record context after both random and
  sequential PUT operations.

  After a PUT operation, the current record pointer has no
  value. However, the value of the next record pointer changes
  depending on the file type and the record access mode used
  with the PUT operation. In a sequential, stream, or variable
  file, records can only be added at the end of the file; therefore,
  the next record after PUT is the end of the file. In a relative,
  sequential, or fixed file, the next record after a PUT operation
  is the next logical record.

  The following example opens a sequential file with ACCESS
  APPEND specified. For sequential files, this is almost iden-
  tical to ACCESS WRITE. The only difference is that, with
  ACCESS APPEND, BASIC positions the file pointer after the
  last record in the file when it opens the file for processing. All
  subsequent PUT operations append the new record to the end
  of the existing file.
  EXAMPLE: Click to display EXAMPLE.

  If the current record pointer is not at the end of the file when
  you attempt a sequential PUT operation to a sequential file,
  BASIC signals ``Not at end of file'' (ERR=149).

  In the following example, the PUT statement writes records
  to an indexed file. In this case, the error message ``Duplicate
  key detected'' (ERR=134) indicates that a record with a
  matching key field already exists, and you did not allow
  duplicates on that key.
  EXAMPLE: Click to display EXAMPLE.

  EXAMPLE: Click to display EXAMPLE.