BASH is not an appropriate standard to use in writing a script.

ShellCheck recognizes three hashbangs, POSIX, BASH, and the Korn shell (as is explained in the manual page). I would argue and assert that BASH is the least relevant of the three.

I have occasionally needed to write to the POSIX standard, and remove advanced features from my scripts. This is most commonly needed for BusyBox (including Windows) and Ubuntu/Debian DASH. It is important to understand what is not in POSIX, for the time when an advanced shell isn't available. Please browse the POSIX definition, reported by a google of "POSIX shell":

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...

The Korn shell lived and diverged for many years, beginning with ksh88 (issued before the first BASH release in 1989). David Korn retired, and AT&T was not pleased with ksh93 changes implemented by outsiders who impacted both compatibility and performance, and thus ksh93 was rewound.

Cygwin, notibly, only implements mksh for Windows. The mksh binary on all platforms is a fraction of the size of BASH (check the output of the "size" command if an "ls" does not persuade you).

However, the MirBSD Korn shell is one of the most lively shells for development activity, the latest release being in October of 2020. It is also on every Android phone (chosen as the system shell by Google), so its deployment is massive.

When I am purposely writing above the POSIX shell, I choose mksh from MirBSD as my standard. I do not think the BASH innovations to be well-thought.