The RECNO keyword specifies that a DISK file is to be processed by relative-record number. The RECNO keyword must be specified for output files processed by relative-record number, output files that are referenced by a random WRITE calculation operation, or output files that are used with ADD on the output specifications.
The RECNO keyword can be specified for input⁄update files. The relative-record number of the record retrieved is placed in the 'fieldname', for all operations that reposition the file (such as READ, SETLL, or OPEN). It must be defined as numeric with zero decimal positions. The field length must be sufficient to contain the longest record number for the file.