｢ POSIX is a specification. Not a program. The thing that actually runs your script is bash, dash, ash, ksh, yash, or one of a dozen others. They each implement POSIX with their own gaps, extensions, and historical accidents ｣
https://alganet.github.io/blog/2026-06-28-12-POSIX-Is-Not-A-Shell.html
@jbz The autoconf manual also contains more information on this, especially regarding historical information on this.
It's an interesting read for any into writing shell scripts.
