joogy06/agent-foundry/cobol-developer

Name: cobol-developer
Author: joogy06

Claude Code and agent skill by joogy06/agent-foundry

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Use when reading, writing, debugging, or modernizing COBOL programs — divisions and sections, data types (PIC clauses, COMP/COMP-3/DISPLAY), file handling (QSAM/VSAM/KSDS/RRDS), PERFORM and paragraph structure, COPY/REPLACE, embedded SQL (EXEC SQL), CICS programming (EXEC CICS), batch JCL integration, debugging (CEDF/Xpediter), and COBOL modernization patterns. Part of the ibm-mainframe skill family.

Install

npx vskill@latest install joogy06/agent-foundry/cobol-developer

SKILL.md

COBOL Developer Reference

Companion to ibm-mainframe (JCL/VSAM/utilities) and db2-mainframe (DB2 z/OS DBA). For Python mainframe connectivity see python-enterprise-connectors.

<HARD-RULE> Always check SQLCODE after every EXEC SQL statement — unchecked SQLCODEs cause silent data corruption. At minimum check for SQLCODE = 0, +100 (not found), and negative values (errors). </HARD-RULE>

<HARD-RULE> Never use GO TO in new COBOL code — use structured PERFORM THRU patterns for maintainability. GO TO creates spaghetti control flow that is nearly impossible to debug or modify. </HARD-RULE>

<HARD-RULE> Always define numeric fields with explicit COMP-3 or COMP for calculations — DISPLAY numeric fields cause implicit conversions on every arithmetic operation, degrading performance significantly in batch loops. </HARD-RULE>

<HARD-RULE> Always initialize WORKING-STORAGE variables with VALUE clauses or INITIALIZE verb — uninitialized fields contain unpredictable data from previous program executions in CICS or residual memory in batch. </HARD-RULE>

1. Program Structure

cobol

       IDENTIFICATION DIVISION.
       PROGRAM-ID. ORDPROC.
       AUTHOR. MAINTENANCE TEAM.
       DATE-WRITTEN. 2026-03-31.
      *================================================================*
      * ORDER PROCESSING - BATCH PROGRAM                               *
      *================================================================*
 
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       SPECIAL-NAMES.
           DECIMAL-POINT IS COMMA.
 
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT ORDER-FILE
               ASSIGN TO ORDIN
               ORGANIZATION IS SEQUENTIAL
               FILE STATUS IS WS-ORDER-FS.
 
           SELECT REPORT-FILE
               ASSIGN TO RPTOUT
               ORGANIZATION IS SEQUENTIAL
               FILE STATUS IS WS-REPORT-FS.
 
           SELECT CUSTOMER-FILE
               ASSIGN TO CUSTDB
               ORGANIZATION IS INDEXED
               ACCESS MODE IS RANDOM
               RECORD KEY IS CUST-KEY
               FILE STATUS IS WS-CUST-FS.
 
       DATA DIVISION.
       FILE SECTION.
       FD  ORDER-FILE
           RECORDING MODE IS F
           RECORD CONTAINS 200 CHARACTERS.
       01  ORDER-RECORD.
           05  ORD-ID              PIC 9(10).
           05  ORD-CUST-ID         PIC 9(8).
           05  ORD-DATE            PIC X(10).
           05  ORD-AMOUNT          PIC S9(11)V99 COMP-3.
           05  ORD-STATUS          PIC X(1).
               88  ORD-PENDING     VALUE 'P'.
               88  ORD-SHIPPED     VALUE 'S'.
               88  ORD-CANCELLED   VALUE 'C'.
           05  FILLER              PIC X(163).
 
       FD  REPORT-FILE
           RECORDING MODE IS F
           RECORD CONTAINS 132 CHARACTERS.
       01  REPORT-RECORD           PIC X(132).
 
       WORKING-STORAGE SECTION.
       01  WS-FILE-STATUS.
           05  WS-ORDER-FS        PIC XX VALUE SPACES.
           05  WS-REPORT-FS       PIC XX VALUE SPACES.
           05  WS-CUST-FS         PIC XX VALUE SPACES.
 
       01  WS-FLAGS.
           05  WS-EOF-FLAG        PIC X(1) VALUE 'N'.
               88  END-OF-FILE    VALUE 'Y'.
               88  NOT-END-OF-FILE VALUE 'N'.
 
       01  WS-COUNTERS.
           05  WS-READ-COUNT      PIC 9(9) COMP VALUE 0.
           05  WS-PROC-COUNT      PIC 9(9) COMP VALUE 0.
           05  WS-ERROR-COUNT     PIC 9(9) COMP VALUE 0.
 
       01  WS-TOTALS.
           05  WS-TOTAL-AMOUNT    PIC S9(15)V99 COMP-3
                                  VALUE ZERO.
 
       PROCEDURE DIVISION.
       0000-MAIN.
           PERFORM 1000-INITIALIZE
           PERFORM 2000-PROCESS UNTIL END-OF-FILE
           PERFORM 9000-TERMINATE
           GOBACK
           .
 
       1000-INITIALIZE.
           OPEN INPUT ORDER-FILE
           OPEN OUTPUT REPORT-FILE
           PERFORM 1100-READ-ORDER
           .
 
       1100-READ-ORDER.
           READ ORDER-FILE
               AT END SET END-OF-FILE TO TRUE
               NOT AT END ADD 1 TO WS-READ-COUNT
           END-READ
           .
 
       2000-PROCESS.
           EVALUATE TRUE
               WHEN ORD-PENDING
                   PERFORM 2100-PROCESS-PENDING
               WHEN ORD-SHIPPED
                   PERFORM 2200-PROCESS-SHIPPED
               WHEN OTHER
                   ADD 1 TO WS-ERROR-COUNT
           END-EVALUATE
           PERFORM 1100-READ-ORDER
           .
 
       9000-TERMINATE.
           CLOSE ORDER-FILE REPORT-FILE
           DISPLAY 'RECORDS READ:      ' WS-READ-COUNT
           DISPLAY 'RECORDS PROCESSED: ' WS-PROC-COUNT
           DISPLAY 'ERRORS:            ' WS-ERROR-COUNT
           .

2. Data Division Deep Dive

PIC Clauses

PIC	Meaning	Example Value
`PIC X(20)`	Alphanumeric, 20 chars	`"JOHN DOE "`
`PIC 9(5)`	Numeric display, 5 digits	`00123`
`PIC S9(7)V99`	Signed, 7 integer + 2 decimal	`+1234567.89`
`PIC S9(7)V99 COMP-3`	Packed decimal (BCD)	4 bytes
`PIC S9(9) COMP`	Binary (fullword)	4 bytes
`PIC S9(18) COMP`	Binary (doubleword)	8 bytes
`PIC S9(7)V99 COMP-1`	Single-precision float	4 bytes
`PIC S9(18)V99 COMP-2`	Double-precision float	8 bytes
`PIC Z(5)9`	Edited numeric (leading zeros suppressed)	`123`
`PIC $ZZ,ZZ9.99`	Edited with currency/commas	`$1,234.56`

Storage Formats

Usage	Storage	When to Use
DISPLAY	1 byte/digit	External files, reports
COMP-3 (packed)	(n+1)/2 bytes	All calculations and DB2 columns
COMP (binary)	2/4/8 bytes	Subscripts, counters, indexes
COMP-1 (float)	4 bytes	Scientific calculations (rare)
COMP-2 (double)	8 bytes	Scientific calculations (rare)

REDEFINES

cobol

       01  WS-DATE-FIELD.
           05  WS-DATE-CCYYMMDD   PIC 9(8).
           05  WS-DATE-PARTS REDEFINES WS-DATE-CCYYMMDD.
               10  WS-DATE-CC     PIC 99.
               10  WS-DATE-YY     PIC 99.
               10  WS-DATE-MM     PIC 99.
               10  WS-DATE-DD     PIC 99.

OCCURS (Arrays)

cobol

       01  WS-MONTHLY-TOTALS.
           05  WS-MONTH-ENTRY OCCURS 12 TIMES
               INDEXED BY WS-MONTH-IDX.
               10  WS-MONTH-NAME  PIC X(10).
               10  WS-MONTH-AMT   PIC S9(11)V99 COMP-3.
 
      * Variable-length array
       01  WS-ORDER-LINES.
           05  WS-LINE-COUNT      PIC 99 COMP.
           05  WS-LINE-ITEM OCCURS 1 TO 50 TIMES
               DEPENDING ON WS-LINE-COUNT.
               10  WS-ITEM-SKU    PIC X(10).
               10  WS-ITEM-QTY    PIC 9(5) COMP-3.
               10  WS-ITEM-PRICE  PIC S9(7)V99 COMP-3.

88-Level Condition Names

cobol

       01  WS-TRANSACTION-TYPE    PIC X(2).
           88  TXN-SALE           VALUE 'SA'.
           88  TXN-RETURN         VALUE 'RT'.
           88  TXN-EXCHANGE       VALUE 'EX'.
           88  TXN-VALID          VALUE 'SA' 'RT' 'EX'.
 
      * Usage:
           IF TXN-VALID
               PERFORM 2000-PROCESS-TXN
           END-IF
 
           SET TXN-SALE TO TRUE    *> Sets WS-TRANSACTION-TYPE to 'SA'

3. File Handling

File Status Codes

Code	Meaning
00	Success
10	End of file (AT END)
22	Duplicate key on WRITE
23	Record not found (READ/START/DELETE)
35	File not found (OPEN)
39	File attribute conflict
41	File already open
42	File already closed
46	Sequential READ with no valid next
47	READ on file not opened INPUT/I-O
48	WRITE on file not opened OUTPUT/I-O/EXTEND

VSAM KSDS (Indexed)

cobol

       FILE-CONTROL.
           SELECT CUSTOMER-FILE
               ASSIGN TO CUSTFILE
               ORGANIZATION IS INDEXED
               ACCESS MODE IS DYNAMIC
               RECORD KEY IS CUST-ID
               ALTERNATE RECORD KEY IS CUST-NAME
                   WITH DUPLICATES
               FILE STATUS IS WS-CUST-FS.
 
      * Random read
           MOVE '00012345' TO CUST-ID
           READ CUSTOMER-FILE
               INVALID KEY
                   DISPLAY 'CUSTOMER NOT FOUND: ' CUST-ID
               NOT INVALID KEY
                   PERFORM 3000-PROCESS-CUSTOMER
           END-READ
 
      * Sequential browse (START + READ NEXT)
           MOVE '00010000' TO CUST-ID
           START CUSTOMER-FILE KEY >= CUST-ID
               INVALID KEY DISPLAY 'START FAILED'
           END-START
           PERFORM UNTIL WS-CUST-FS NOT = '00'
               READ CUSTOMER-FILE NEXT
                   AT END SET END-OF-FILE TO TRUE
               END-READ
               IF NOT END-OF-FILE
                   PERFORM 3000-PROCESS-CUSTOMER
               END-IF
           END-PERFORM
 
      * Update
           READ CUSTOMER-FILE
               INVALID KEY DISPLAY 'NOT FOUND'
           END-READ
           MOVE 'ACTIVE' TO CUST-STATUS
           REWRITE CUSTOMER-RECORD
               INVALID KEY DISPLAY 'REWRITE FAILED'
           END-REWRITE

SORT/MERGE

cobol

       SD  SORT-FILE.
       01  SORT-RECORD.
           05  SORT-KEY           PIC 9(10).
           05  SORT-DATA          PIC X(190).
 
       PROCEDURE DIVISION.
      * Simple sort
           SORT SORT-FILE
               ON ASCENDING KEY SORT-KEY
               USING INPUT-FILE
               GIVING OUTPUT-FILE
 
      * Sort with INPUT/OUTPUT PROCEDURE
           SORT SORT-FILE
               ON ASCENDING KEY SORT-KEY
               INPUT PROCEDURE IS 5000-SELECT-RECORDS
               OUTPUT PROCEDURE IS 6000-FORMAT-OUTPUT
 
       5000-SELECT-RECORDS.
           OPEN INPUT RAW-FILE
           PERFORM UNTIL END-OF-RAW
               READ RAW-FILE AT END SET END-OF-RAW TO TRUE
               NOT AT END
                   IF RAW-STATUS = 'A'
                       MOVE RAW-RECORD TO SORT-RECORD
                       RELEASE SORT-RECORD
                   END-IF
               END-READ
           END-PERFORM
           CLOSE RAW-FILE
           .
 
       6000-FORMAT-OUTPUT.
           OPEN OUTPUT FINAL-FILE
           PERFORM UNTIL END-OF-SORT
               RETURN SORT-FILE
                   AT END SET END-OF-SORT TO TRUE
                   NOT AT END
                       PERFORM 6100-WRITE-FORMATTED
               END-RETURN
           END-PERFORM
           CLOSE FINAL-FILE
           .

4. Procedure Division Patterns

STRING / UNSTRING

cobol

      * STRING — concatenate
           STRING WS-LAST-NAME DELIMITED BY SPACES
                  ', '           DELIMITED BY SIZE
                  WS-FIRST-NAME DELIMITED BY SPACES
             INTO WS-FULL-NAME
             WITH POINTER WS-STR-PTR
             ON OVERFLOW DISPLAY 'NAME TOO LONG'
           END-STRING
 
      * UNSTRING — split
           UNSTRING WS-CSV-LINE DELIMITED BY ','
             INTO WS-FIELD1
                  WS-FIELD2
                  WS-FIELD3
             WITH POINTER WS-UNS-PTR
             TALLYING IN WS-FIELD-COUNT
             ON OVERFLOW DISPLAY 'TOO MANY FIELDS'
           END-UNSTRING

INSPECT

cobol

      * Count occurrences
           INSPECT WS-INPUT-STRING
               TALLYING WS-COUNT FOR ALL 'A'
 
      * Replace characters
           INSPECT WS-INPUT-STRING
               REPLACING ALL LOW-VALUES BY SPACES
 
      * Convert (translate)
           INSPECT WS-INPUT-STRING
               CONVERTING 'abcdefghijklmnopqrstuvwxyz'
               TO         'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

Reference Modification

cobol

      * Extract substring: identifier(start:length)
           MOVE WS-FULL-DATE(1:4) TO WS-YEAR    *> First 4 chars
           MOVE WS-FULL-DATE(5:2) TO WS-MONTH   *> Chars 5-6
           MOVE WS-FULL-DATE(7:2) TO WS-DAY     *> Chars 7-8

CALL (Subprogram)

This is the start of the file. Read the full SKILL.md on GitHub.

Security

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Source

SKILL.md in the repositoryCheckingskills/cobol-developer/SKILL.md

Popularity

Repository stars: 2
7-day trend score: 5

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