Line number parameter

The line number parameter (parameter 5) is not used for the INIT, OPENR, OPENW, OPENX, TERM, or CLOSE functions. The parameter is used as an input parameter for the WRITE function and as an output parameter for the READ and READX functions.

If you are writing to a DD that is opened for update, you can use this parameter to verify the record being updated. The parameter must be either:

A non-zero number that is checked against the record number of the last record that was read for update. This ensures that the correct record is updated. If the record numbers are identical, the record is updated. If not, the record is not written and a return code of 20 is returned.
0 - No record verification is done. The last record that was read is unconditionally updated.

If you are writing to a DD that is opened for output, the line number parameter is ignored.

On output for the READ or READX functions, the parameter returns the absolute record number of the last logical record that was read.