Re: How to change the shebang in 'configure' to require Bash

[R. Diez]

> I saw in the recent Automake release notes that there’s a tentative plan that
> Autoconf 2.0 will require at least a POSIX shell.
>
> Herr Diez, is this close enough to “Bash” to suit your purposes?
> That is, are you just looking for things like $() instead of ``, > or are you 
> intending to commit outright bash-isms?

First of all, thanks for your answer.

I know that Autoconf developers want to write extremely portable 
scripts. But that is a huge barrier for somebody like me. I am a user, 
not a shell expert.

I have heard that the POSIX standard, or maybe its implementation, is 
not exactly the same across all shells. There are subtle differences.

The generated 'configure' script changes shells on start-up. The logic 
is not documented. I looked inside, and it was not immediately obvious 
on what grounds some shells are preferred. Depending on what is 
installed, I seems possible that zsh is taken, for example.

I am unwilling to test my configure.ac on several shells. Furthermore, 
the features in the POSIX standard are very limited. I am using arrays 
and regular expressions, for example. An my scripts are not really that 
complex.

In any case, the behaviour of my configure.ac script cannot depend on 
what shells the end-user has currently installed. I do not know of any 
shell linters like ShellCheck that accept configure.ac files.

I would be very happy if my software ran on 10 % of the platforms where 
Bash is installed by default. Therefore, demanding Bash is for me the 
best solution.

In fact, it is the only sane solution. Not even hard-core Autoconf 
developers should take such risks. My guess is that Autoconf-generated 
'configure' scripts usually work because they tend to switch to Bash on 
start-up.

Even if you really wanted, there is no way to properly test your 
configure.ac scripts. Autoconf requires a Bourne shell, but exactly what 
is required, is not documented. There is no guide as to what shells and 
shell versions you should be testing against.

Autoconf works because most bugs have been reported and fixed over many 
years. But trying to change the shell requirement now is probably a big 
nightmare.

Requiring a POSIX shell in the next version is an improvement, but POSIX 
is too limiting to really help. It is 2018. No wonder so many people 
want to ditch Autoconf!

Best regards,
  R. Diez