What lives here

Fifty short lessons, one unbroken chain: every page ends with a link to the next one, so you can read the course start to finish without ever wondering where to click. Each lesson teaches one idea with short COBOL examples, and the longer deep dives live on their own pages under COBOL:

1. Start here: What is COBOL and where it runs - then follow the chain through lesson 50.
2. Language core, lessons 2-20: install, the compiler, first program, divisions, variables, numbers, strings, constants, conditions, IF and EVALUATE, PERFORM, tables, indexes, paragraphs, STRING, files, sequential IO, errors, and copybooks.
3. Objects and tooling, lessons 21-30: OO COBOL, inheritance, intrinsic functions, idioms, builds, testing, debugging, encodings, date and time, JSON and XML.
4. The enterprise world, lessons 31-45: C interop, subprograms, embedded SQL, DISPLAY, ACCEPT, the Report Writer, SORT, arguments, environment, logging, CSV, CICS, batch and JCL, file status, and Db2 in practice.
5. Finish, lessons 46-50: two capstones (CLI calculator and file processor), performance, modern COBOL tour, and the hero roadmap with every lesson on one page.

Course tree

Chapter 0: Install guides ├── Install COBOL on Windows 11 ├── Install COBOL on Ubuntu ├── Install COBOL on Rocky Linux ├── Install COBOL on macOS ├── Install COBOL on FreeBSD └── COBOL in Docker Chapter 1: First steps ├── 01 What is COBOL and where it runs ├── 02 Install COBOL and check the version ├── 03 cobc: the COBOL compiler └── 04 Your first COBOL program Chapter 2: Data and control flow ├── 05 The four divisions ├── 06 Variables and PICTURE clauses ├── 07 Numbers: USAGE, COMP and COMP-3 ├── 08 Alphanumeric fields (strings) ├── 09 Constants: level 78 and VALUE ├── 10 Conditions and relation tests ├── 11 IF, ELSE and EVALUATE ├── 12 PERFORM loops ├── 13 Tables: OCCURS arrays └── 14 INDEXED BY and OCCURS DEPENDING ON Chapter 3: Procedures and IO ├── 15 Paragraphs and sections ├── 16 STRING and UNSTRING ├── 17 Files: SELECT and FD ├── 18 Sequential files: READ and WRITE ├── 19 Error handling: USE and DECLARATIVES └── 20 Copybooks and COPY Chapter 4: Objects and tooling ├── 21 OO COBOL: classes and objects ├── 22 Inheritance in OO COBOL ├── 23 Intrinsic functions ├── 24 COBOL idioms and clean code ├── 25 Build tools: make and cobc flags ├── 26 Testing COBOL programs ├── 27 Debugging: cobcdebug and -g ├── 28 Encodings: EBCDIC, ASCII and UTF-8 ├── 29 Date and time └── 30 JSON and XML Chapter 5: The enterprise world ├── 31 Calling C functions ├── 32 Subprograms: CALL and USING ├── 33 SQL with EXEC SQL ├── 34 DISPLAY and formatting ├── 35 ACCEPT and the SCREEN section ├── 36 The Report Writer ├── 37 Sorting with the SORT verb ├── 38 Command-line arguments ├── 39 Environment and RETURN-CODE ├── 40 Logging to files ├── 41 CSV parsing ├── 42 CICS overview ├── 43 Batch processing and JCL ├── 44 File status and transactions └── 45 Db2 in practice Chapter 6: Capstones and finish ├── 46 Capstone: CLI calculator ├── 47 Capstone: fixed-width file processor ├── 48 Performance: tuning COBOL ├── 49 Modern COBOL tour (2014+) └── 50 Hero roadmap: the whole course on one page Bonus: COBOL on mainframes └── COBOL on mainframes

How to use this course

Type every example, do not just read it. Compile each snippet with cobc -x -free before moving on - the course assumes your hands remember lesson 4 by the time lesson 16 arrives.

The classic COBOL rules apply from day one: uppercase verbs, PIC clauses for every field, and a period at the end of every sentence.