Hint: it's not Bash. That would be sh, which is not really portable--if it were, autoconf wouldn't spend so much effort on portability.
So yes, can anyone provide such a list please?
Awk and perl.
I use a lot of bash though.
About 7 years ago I had a job where we supported almost every Unix all the way back to AT&T SVR3 (including OpenServer, UnixWare, HP-UX, AIX, Linux, OSF/1). With the exception of SVR3 every single one had binary packages for Perl 5.
until you run embedded routers and such, where perl is too large and bash/ash/mush rules.
Or you're bootstrapping an install process and perl isn't included, but a shell is.
Perl, it's everywhere, and is a better bash than bash is.