Reference modification

Often you need part of a field: the year of a date, the last four digits of a card number, the first letter of a name. Reference modification lets you address any substring of a data item without declaring a subfield for it:

identifier(start:length)

start is the 1-based position of the first byte, length is how many bytes. Leave out the length to mean "to the end of the field".

       IDENTIFICATION DIVISION.
       PROGRAM-ID. REFMOD.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-DATE      PIC X(8)  VALUE "20260924".
       01  WS-NAME      PIC X(12) VALUE "HOPPER".
       PROCEDURE DIVISION.
           DISPLAY WS-DATE(1:4) "-" WS-DATE(5:2) "-" WS-DATE(7:)
           DISPLAY "INITIAL: " WS-NAME(1:1)
           STOP RUN.

Output:

2026-09-24
INITIAL: H

Variables as positions

Both start and length can be numeric data items or arithmetic expressions, which makes reference modification the way to walk through a field one character at a time:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. SPELL.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-WORD      PIC X(5)  VALUE "COBOL".
       01  WS-I         PIC 9(2).
       PROCEDURE DIVISION.
           PERFORM VARYING WS-I FROM 1 BY 1 UNTIL WS-I > 5
               DISPLAY WS-I ": " WS-WORD(WS-I:1)
           END-PERFORM
           STOP RUN.

This prints 01: C, 02: O, and so on. WS-WORD(WS-I + 1:2) works too.

As a receiving field

A reference-modified item can be the target of a MOVE. Only the addressed bytes change; the rest of the field is untouched:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. MASK.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  WS-ACCT      PIC X(10) VALUE "4400123987".
       PROCEDURE DIVISION.
           MOVE ALL "*" TO WS-ACCT(1:6)
           DISPLAY WS-ACCT
           STOP RUN.

Output: ******3987. MOVE ALL "*" fills the whole receiving area (here six bytes) with asterisks.

Things to watch

• The result of reference modification is always alphanumeric, even if the field is numeric. WS-AMOUNT(1:3) gives you three digit characters, not a number.
• Positions are not checked by default. WS-DATE(7:5) on an 8-byte field reads past the end into whatever is next in storage. On the mainframe, compile with SSRANGE during testing to catch this.
• Positions count bytes. On the mainframe, text is EBCDIC, one byte per character, so this is rarely a surprise.