Re: GNU Automake 1.15.1 released

[Warren Young]

On Jun 19, 2017, at 2:50 PM, Mathieu Lirzin <address@hidden> wrote:
> 
>  - Automake-provided scripts and makefile recipes might (finally!)
>    start assuming a POSIX shell in Automake 2.0.  There still is no
>    certainty about this though: we'd first like to wait and see
>    whether future Autoconf versions will be enhanced to guarantee
>    that such a shell is always found and provided by the checks in
>    ./configure.

Please clarify: does this apply to the shell script code written in *.m4 files 
included in the output configure script or to shell script code written in the 
user’s configure.ac file?

Currently, it’s the end user’s look-out if they do this.  What I’m suggesting 
is that it is possible for Autoconf to bend over backwards to ensure that the 
generated configure script runs under a local POSIX shell, if available, 
thereby making possible use of POSIX shell features in end-user macros and such 
even on systems where /bin/sh is not a POSIX shell.

As I understand it, the main difficulty here is that the generated configure 
script can’t start with anything other than #!/bin/sh for portability.  My 
suggestion is that one of the first things the generated code do is test 
whether it is running under a POSIX shell, and if not, try to find one and 
re-exec itself under that shell instead. 

It’s generally possible to find a POSIX-compatible shell somewhere on the 
system these days if you only look hard enough: /usr/xpg4/bin/sh on old 
Solaris, /bin/bash on Linuxes where /bin/sh is pre-POSIX, /usr/bin/ksh on some 
SVR4 systems, etc.

Even the shells built into Busybox are fairly POSIX-compliant these days.