Here are questions someone could ask. Read it! It could answer some of your questions.
Most coreutils are either non-POSIX or use non-portable functions not specified by POSIX.
In contrast, we separate POSIX and non-POSIX utilities, and on all utilities (including non-POSIX ones) we make sure we use only POSIX functions, regardless of if a non-POSIX function is already implemented in many C libraries.
Please though, please do not trash those other coreutils. The fact that they're not fully POSIX doesn't mean they're bad. In fact, some of the non-POSIX features might actually be useful for some people. Thanks!
Well, it depends on the system itself. If your system implements POSIX functions in its C library, then it'll work. Utilities are currently tested on:
Some people might see that
If you're interested in becoming a co-maintainer, please reach out!