OUTREC statement with OVERLAY is used to insert sequence numbers into records. This is useful for numbering records sequentially, either starting from a specific value or using a specific increment.

Syntax1 - Simple sequence number generation

//SYSIN    DD *
  SORT FIELDS=COPY
  OUTREC OVERLAY=(...,
         starting_pos_in_output_file:SEQNUM,
         seqnum_length,seqnum_format,...)
/*

Syntax2 - Sequence number generation with custom increment

//SYSIN    DD *
  SORT FIELDS=COPY
  OUTREC OVERLAY=(...,
         starting_pos_in_output_file:SEQNUM,
         seqnum_length,seqnum_format,
		 START=starting_seq_num,
		 INCR=seqnum_increment_by,
		 RESTART=(field1_starting_pos,
		 field1_length),...)
/*

starting_pos_in_output_file	Specifies the position from where the sequence number to start in output file
SEQNUM	Specifies a keyword to generate the sequence number
seqnum_length	Specifies the length of the sequence number
seqnum_format	Specifies the format of the sequence number
START=starting_seq_num	Specifies the starting sequence number with
INCR=seqnum_increment_by	Specifies the number that used to increment
RESTART=(field1_starting_pos,field1_length)	Specifies the field starting position and length on which the sequence number restart

Examples -

Scenario1 - Inserting sequence numbers with default start and increment.

//SYSIN   DD  *
  SORT FIELDS=COPY
  OUTREC FIELDS=(1,20,21:SEQNUM,5,ZD)
/*

Inserts a 5-byte zoned decimal sequence number starting at position 21. The sequence starts from 1 by default and increments by 1.

Scenario2 - Inserting sequence numbers with custom start and increment.

//SYSIN   DD  *
  SORT FIELDS=COPY
  OUTREC FIELDS=(1,30,31:SEQNUM,6,ZD,START=1000,INCR=10)
/*

Inserts a 6-byte zoned decimal sequence number starting at position 31. The sequence starts at 1000 and increments by 10 for each record.

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