Debian has ongoing efforts to make many shell scripts (like postinst Scripts in packages etc.) non-bash-specific.
A minimal Debian installation doesn't contain bash, but rather dash, which doesn't support bash extensions.
Please don't make up wrong facts that would be trivial to check first.
All minimal Debian installations include bash as it is an essential package. Where essential is used in the sense of https://www.debian.org/doc/debian-policy/ch-binary.html#esse...
For clarity, 'sh' is what is softlinked to dash. Not bash.
