I’m curious too, my understanding is that 90% of COBOL work is done in older mainframes (or ported from older mainframes to newer ones) and likely uses whatever IBM compilers. I don’t think I’ve ever heard of GnuCOBOL being used outside of learning.

In my (very limited) z/OS experience, COBOL by itself is necessary but not nearly sufficient. COBOL code is used inside a framework of highly proprietary software and system services:

- DB2 (database is builtin to the mainframe)

- GDG (Generation Data Groups, versioned file system)

- ACL (IBM's original access control lists)

- JCL (automation, parameters, logging)

- SyncSort (data sorting, joining)

- various CA Technologies products

- etc!

Don't forget CICS (OLTP component). But spot on...a mainframe is an ecosystem, not a language.

Probably not hard for you to guess that my experience is limited entirely to enterprise batch processing and data warehousing. I've heard of CICS, but only as a nasty rumor.

Yep this is why I'm also weary of people who suggest to "just learn COBOL" for a job.