Re: #! -- reconsideration?

[Maurice Cinquini <mcinquini@speedera.com>]

Dan Kegel wrote:
> 
> Don Cragun wrote:
> >         The POSIX standards and the Single UNIX Specifications have
> > wisely chosen not to specify hard coded pathnames for the standard
> > utilities.  Implementations need to give users a description of how to
> > find the set of utilities specified by the standards they support, and
> > the standards need to specify how to find the rest of the standard
> > utilities once you get to that point (such as Austin Group revision
> > draft 3 XCU's
> >                  -v specification PATH
> > command.)  Then applications that want to use #! have to be configured
> > to find the absolute pathname for the utility they want invoked as the
> > interpreter by #! as part of their installation processing.
>
> So you're proposing that a package that wants to be portable will
> rewrite all of its shell scripts at install time and replace the thing
> following #! with the absolute path to the POSIX-compliant shell
> located in the first directory listed in `getconf PATH`?
> 
> That's reasonable, I suppose, but it's not something I've seen done
> in practice yet.  Has anyone else observed this in the wild?

Attached is the relevant fragment from perl's Configure that determines
what the first line should be.  It is written in bourne shell.
It doesn't use getconf and works even for for non-posix systems that
require ": use" instead of "#!".  nce this first line is determined,
it is saved away for later use when creating shell scripts.

______________________________________________________________________

Maurice Cinquini            Senior Software Engineer
mcinquini@speedera.com      Speedera Networks
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: Find the basic shell for Bourne shell scripts
case "$sh" in
'')
	case "$SYSTYPE" in
	*bsd*|sys5*) xxx="/$SYSTYPE/bin/sh";;
	*) xxx='/bin/sh';;
	esac
	if test -f "$xxx"; then
		sh="$xxx"
	else
		: Build up a list and do a single loop so we can 'break' out.
		pth=`echo $PATH | sed -e "s/$p_/ /g"`
		for xxx in sh bash ksh pdksh ash; do
			for p in $pth; do
				try="$try ${p}/${xxx}"
			done
		done
		for xxx in $try; do
			if test -f "$xxx"; then
				sh="$xxx";
				break
			elif test -f "$xxx.exe"; then
				sh="$xxx";
				break
			fi
		done
	fi
	;;
esac

case "$sh" in
'')	cat <<EOM >&2
$me:  Fatal Error:  I can't find a Bourne Shell anywhere.  

Usually it's in /bin/sh.  How did you even get this far?
Please contact perlbug@perl.com and we'll try to straighten this all out.
EOM
	exit 1
	;;
esac

: see if sh knows # comments
if `$sh -c '#' >/dev/null 2>&1`; then
	shsharp=true
	spitshell=cat
	xcat=/bin/cat
	test -f $xcat || xcat=/usr/bin/cat
	echo "#!$xcat" >try
	$eunicefix try
	chmod +x try
	./try > today
	if test -s today; then
		sharpbang='#!'
	else
		echo "#! $xcat" > try
		$eunicefix try
		chmod +x try
		./try > today
		if test -s today; then
			sharpbang='#! '
		else
			sharpbang=': use '
		fi
	fi
else
	echo " "
	echo "Your $sh doesn't grok # comments--I will strip them later on."
	shsharp=false
	cd ..
	echo "exec grep -v '^[ 	]*#'" >spitshell
	chmod +x spitshell
	$eunicefix spitshell
	spitshell=`pwd`/spitshell
	cd UU
	echo "I presume that if # doesn't work, #! won't work either!"
	sharpbang=': use '
fi
rm -f try today

: figure out how to guarantee sh startup
case "$startsh" in
'') startsh=${sharpbang}${sh} ;;
*)
esac
cat >try <<EOSS
$startsh
set abc
test "$?abc" != 1
EOSS

chmod +x try
$eunicefix try
if ./try; then
	: echo "Yup, it does."
else
	echo "Hmm... '$startsh' does not guarantee sh startup..."
	echo "You may have to fix up the shell scripts to make sure $sh runs them."
fi
rm -f try