cob2csv

A pair of command-line tools written in pure COBOL that convert fixed-width flat files to CSV and back. Built with GnuCOBOL, no mainframe required.

Tools

Tool	Direction
cob2csv	Fixed-width COBOL flat file → CSV
csv2cob	CSV → Fixed-width COBOL flat file

Requirements

sudo apt install gnucobol   # Ubuntu/Debian
brew install gnucobol       # macOS

Build

make

Binaries are placed in bin/.

Usage

cob2csv — flat file to CSV

cob2csv -s schema.cfg -i input.dat -o output.csv

# or pipe to stdout
cob2csv -s schema.cfg -i input.dat

csv2cob — CSV to flat file

csv2cob -s schema.cfg -i input.csv -o output.dat

Flags

Flag	Long form	Description
-s	--schema	Schema config file (required)
-i	--input	Input file (required)
-o	--output	Output file (default: stdout for cob2csv)

Schema format

Define your record layout in a plain .cfg file. Each FIELD line describes one column:

# customer.cfg
FIELD NAME=CUST-ID     START=1   LENGTH=6   TYPE=NUM
FIELD NAME=FIRST-NAME  START=7   LENGTH=15  TYPE=ALPHA
FIELD NAME=LAST-NAME   START=22  LENGTH=15  TYPE=ALPHA
FIELD NAME=BALANCE     START=37  LENGTH=9   TYPE=DECIMAL DECIMALS=2
FIELD NAME=STATE       START=46  LENGTH=2   TYPE=ALPHA

Key	Description
NAME	Column name (used as CSV header)
START	1-based start position in the fixed-width record
LENGTH	Field length in characters
TYPE	ALPHA, NUM, or DECIMAL
DECIMALS	Number of implied decimal places (DECIMAL type only)

Types

• ALPHA — Text. Left-justified in output, space-padded in flat file. Quoted in CSV if the value contains a comma or quote.
• NUM — Integer. Right-justified, zero-padded in flat file. Leading zeros stripped in CSV.
• DECIMAL — Implied decimal (no decimal point stored). LENGTH=9 DECIMALS=2 means 7 integer digits + 2 fractional digits. Decimal point inserted on CSV output.

Running tests

make test

Tests use diff to compare actual output against expected fixtures, no test framework needed.

Examples

See the tests/ directory for a working customer schema and data file. The examples/ directory contains additional schema samples.

Why COBOL?

Fixed-width flat files are COBOL's native habitat. Banks, insurers, and government agencies still produce them by the millions. This tool is written in the same language that generated those files, which means it handles the data model correctly by design, not by approximation.

License

cob2csv is free for personal and non-commercial use under the PolyForm Noncommercial License 1.0.0.

If you or your organization want to use cob2csv in a commercial context, a commercial license is required. Please refer to COMMERCIAL.md