Find official POSIX and UNIX documentation

The best resource I've found is the bash-hackers.org wiki for all things related to Bash. It's what the man pages should be instead of massive pile that's tough to navigate.

There are specific topics on the builtins including printf. This page is exhaustive! It includes all the formatting options as well as examples and even a discussion section at the bottom for helping to flesh our corner cases and nuances with printf's functionality.

I've also been known to use the GNU Coreutils documentation on printf, specifically the page on the formatting options, in a pinch.

There is no standard way to retrieve the list of configuration variables that are supported on a system. If you program for a given POSIX version, the list in that version of the POSIX specification is your reference list. On Linux, getconf -a lists all available variable.

fpathconf isn't specific to PATH. It's about variables that are related to files, which are the ones that may vary from file to file.

Regarding ARG_MAX on Linux, the rationale for depending on the stack size is that the arguments end up on the stack, so there had better be enough room for them plus everything else that must fit. Most other implementations (including older versions of Linux) have a fixed size.

Most limits go together with resource availability, with different resources depending on the limit. For example, a process may be unable to open a file even if it has fewer than OPEN_MAX files open, if the system is out of memory that can be used for the file-related data.

Linux is POSIX-compliant on this point by default, so I don't know where you're getting at.

If you use ulimit -s to restrict the stack size to less than ARG_MAX, you're making the system no longer compliant. A POSIX system can typically be made non-compliant in any number of ways, including PATH=/nowhere (making all standard utilities unavailable) or rm -rf /.

The value of ARG_MAX in limits.h provides a minimum that applications can rely on. A POSIX-compliant system is allowed to let execve succeed even if the arguments exceed that size. The guarantee related to ARG_MAX is that if the arguments fit in that size then execve will not fail due E2BIG.