That's not specifically bash though, that's process exit codes

Yes. But it's still contradictory

The question you are asking when querying a process exit code is "did this program exit with an error?". The default assumption is "no, it completed successfully", so 0 (false) is the logical expected default return.

A function is expected to produce a result - so the question is "what was the result?". !0 (something) is the logical expected default return.

I've never found it to be contradictory.

But in shell, 0 is true, not false. The program called true returns 0.

"True has 0 errors" is the straightforward part.

"False pretends to have an error" is where it gets weird. It's not that they got booleans backwards, it's that they're stretching a tenuous analogy a bit too far.

> The default assumption is "no, it completed successfully"

Correct

> so 0 (false) is the logical expected default return.

Nope

We came to expect zero because we got accustomed to it. And it is a "good enough solution" in memory constrained systems.

And note some programs attribute >0 and <0 to different types of errors

Error code 0 means success in a lot more places than just bash.