gistfile1.sh

#!/bin/bash

# get the Mac OS X version
version_major=$(sw_vers -productVersion | cut -d . -f 2)
#version_minor=$(sw_vers -productVersion | cut -d . -f 3)

interpreter=''
# 10.7.x now has no 32-bit only version of Perl included, so we
# need to set Perl's prefer-32-Bit default
if [ $version_major -eq 7 ]; then
	if [ "$(defaults read com.apple.versioner.perl Prefer-32-Bit)" != "1" ]; then
		printf "Mac OS X 10.7.x Lion requires that we set Perl's 'Prefer-32-Bit' default for %s to work properly.\n" "$1"
		printf "Shall we do that for you (y/n)?"
		read confirm
		if [ "$confirm" = "y" ]; then
			defaults write com.apple.versioner.perl Prefer-32-Bit -bool true
			printf "Done. You can change this back at any time by running 'defaults write com.apple.versioner.perl Prefer-32-Bit -bool false'.\n"
		else
			printf "No change made. Exiting.\n"
			exit 1
		fi
	fi
	interpreter='/usr/bin/perl'
# 10.6.x should use Perl 5.8.9
elif [ $version_major -eq 6 ]; then
	interpreter='/usr/bin/perl5.8.9'
# 10.5.x should use Perl 5.8.8
elif [ $version_major -eq 5 ]; then
	interpreter='/usr/bin/perl5.8.8'
# 10.4.x and earlier can use just use 'perl'
elif [ $version_major -le 4 ]; then
	interpreter='/usr/bin/perl'
fi

# Perl tries to be helpful and always honors the shebang/hashbang in the script
# it executes, but that causes an infinite loop due to what we're doing. So we
# have to strip out the shebang/hashbang before sending to Perl. To do that,
# because Perl can't accept command line arguments when running a script from
# stdin, we must write the script, sans the shebang, to a tmp file.

# determine the command name & shift it off the stack of arguments
full_command="$1"
command="${full_command##*/}"
shift

# create the tmp Perl script and fill it with the original script, sans the
# shebang/hashbang
mkdir -p "/tmp/32bitSafePerl"
touch "/tmp/32bitSafePerl/${command}.tmp.pl"
chmod 755 "/tmp/32bitSafePerl/${command}.tmp.pl"
tail -n+2 "$full_command" > "/tmp/32bitSafePerl/${command}.tmp.pl"

# run the new temp Perl script through the appropriate version of Perl w/the
# command line arguments
"$interpreter" "/tmp/32bitSafePerl/${command}.tmp.pl" "$@"

# clean up the temp Perl script
rm "/tmp/32bitSafePerl/${command}.tmp.pl"

Looks like a good solution to the Perl dilemma.

Thanks, it's been a long work in progress. It's going to get nastier shortly, but it'll work and be very flexible. I like solutions that are as transparent as possible to the end user... these are for Mac users, after all, even if they're technically inclined!

The things that got me (and I only just figured out today) are: that BSD (and so OS X), unlike Linux, shebangs/hashbangs aren't recursive, so you can't call a script from a shebang/hasbang, only binaries; and that Perl will always run the shebang in the file, even if called explicitly because it wants to be helpful and support shebangs/hashbangs under OSes & shells that don't... which creates an infinite loop. Makes for a much more complicated wrapper than I was ever anticipating.

Fun stuff, but this project has always been about the learning experience for me.

The final solution. Works in my general test cases, but I'll need to stress test it.