I learned recently that Windows has system error codes for process errors: https://docs.microsoft.com/en-us/windows/win32/debug/system-...

A coworker mentioned that programs should return internal state information using codes < 0, but I have not fact checked that.

The typical codes I see used today are:

0 = OK 1 = unexpected error 2 = usage error

And then signal codes, which are either 127 or 128 (I forget which) + the signal code.

Anything beyond that is meaningless since because it's not enforced anywhere it's not reliable to use in scripting less you specifically target that version of the program.

I never knew these existed, I wonder how widespread their use is. But from now on.. I'll use them :)

Many but not all are also in Python:

https://docs.python.org/3/library/os.html#os.EX_OK

I put together an enumeration to make it cross platform:

https://gist.github.com/kkirsche/2adb8c94794048ec30736b8fe5f...