GnuCOBOL mainframe batch

Compile and run

cobc -x -free -o prog PROG.cbl
./prog

-free allows *> comments and free-form source. File names in SELECT are resolved relative to the program's run directory.

SELECT DETAIL-FILE ASSIGN TO "TRAN.DAT"
    ORGANIZATION IS SEQUENTIAL.

For 80-byte fixed-record tapes use ORGANIZATION IS SEQUENTIAL with RECORD CONTAINS 80 CHARACTERS in the FD. Pad WRITE records to the required length (e.g. MOVE SPACES TO BAL-REC before populating fields).

PIC and signed amounts

When a tape stores sign and magnitude in separate positions (PIC X plus PIC 9(11)V99), build a signed working-storage value before ADD / SUBTRACT. Using only the unsigned magnitude in EVALUATE branches is a frequent bug when debits and credits share the same magnitude field.

COMPUTE … ROUNDED rounds half away from zero in GnuCOBOL (matches the Python Decimal ROUND_HALF_UP behaviour). Use it when multiplying a two-decimal amount by a four-decimal rate and storing into a two-decimal field.

Debug loop

1. cobc -x -free -Wall -o prog PROG.cbl
2. DISPLAY intermediate values for one or two records to confirm the posting math and any cross-file lookups.
3. Reconcile against a short script that applies the task's posting rules to the same tape layout.

References

• GnuCOBOL programmer's guide
• IBM Enterprise COBOL language reference for PIC/USAGE and file control when porting z/OS sources