On Jun 19, 2017, at 2:50 PM, Mathieu Lirzin <m...@gnu.org> 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.
