When updating a RECFM=V external file in place, ensure that the length of each logical record is not changed when fields' values are changed. If the update operation shortens the logical record, an additional end-of-record marker is written to the file. If lengthened, the updated record is either truncated to the length of the original record if SHAREBUFFERS is not used, or overwrites data on the subsequent record if SHAREBUFFERS is used.

To prevent unexpected results, if the length of the updated record is shorter than the original, the updated record should be padded with blanks to ensure the original end-of-record marker is overwritten. To accomplish this, use the LENGTH= option on the INFILE in conjunction with the $VARYINGw. format, as in this example:

If the update operation might lengthen any logical records, a different file name should be specified in the FILE statement.

Operating System and Release Information