I didn't realise point 2) - that we use Dash in the basic.mk step. I may have noticed it and forgot.

The wider task name makes sense.

I agree on the question of portability, but we also want long-term reproducibility, and we don't want to sacrifice security. :)

With the anecdote: do you mean people using a shell (binary) that was written in 2006? or that the shell script was written in 2006?

I think that we should only require compatibility with an open-access standard. https://en.wikipedia.org/wiki/POSIX#Versions

• POSIX.1-2001 =  IEEE Std 1003.1-2001 = Single UNIX Specification version 3 - but this is not open-access: http://www.unix.org/version3/online.html https://publications.opengroup.org/t041

"This document set for the Single UNIX Specification, Version 3 (UNIX 03). The PDF documents are only available to employees of members of The Open Group."

• IEEE Std 1003.1-2004 does seem to be online: https://pubs.opengroup.org/onlinepubs/009695399/
• https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/ - "POSIX.1-2008 is simultaneously IEEE Std 1003.1-2008 and The Open Group Technical Standard Base Specifications, Issue 7"

Section 2.6.2 of POSIX.1-2008 - https://pubs.opengroup.org/onlinepubs/9699919799.2008edition/ - seems to give the equivalent of POSIX-1.2017 - for requiring ${parameter} to be recognised.

These pages seem to be well-archived: https://web.archive.org/web/20200516232627/https://pubs.opengroup.org/onlinepubs/009695399/ lists 459 snapshots for the top page.

How about 1) IEEE Std 1003.1-2004; 2)+3) POSIX.1-2017 ?

I don't know if there exists an informal name POSIX.1-2004 for IEEE Std 1003.1-2004.

It appears that a shell satisfying POSIX.1-2017 standards must correctly process

${expression}

and

${parameter}

See https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02

It seems to be a general recommendation to write ${parameter} rather than $parameter:
https://stackoverflow.com/questions/8748831/when-do-we-need-curly-braces-around-shell-variables#8748880

There are also recommendations to use double quotes:
https://unix.stackexchange.com/questions/4899/var-vs-var-and-to-quote-or-not-to-quote

Do we have any good reasons not to use {} around parameter names in either (i) the generic POSIX shell or (ii) the GNU bash shell?