The last couple of days I've spent re-building DWIM Perl for Linux using a cpanfile, carton, running builds on Travis-CI and on a Digital Ocean Droplet. DWIM Perl for Linux is a batteries included binary distribution of standard perl + lots of CPAN modules. The hope that it will make it extremely easy for people to get started using Perl. Without the need to encounter the installation headaches that might come with cpan.

I have plenty of things to write about each one of the subjects, but I've encountered an issue that I am not sure how to solve. I wanted to install Test::Differences (as a prerequisite of a a lot of things). It uses $Config{perlpath} instead of more common $^X to run some external perl scripts from some of the test files. This blows up during build with Can't exec "/home/dwimperl/dwimperl-linux-5.20.1-1-x86_64/perl/bin/perl": No such file or directory.

Apparently there is a subtle difference between $Config{perlpath} and $^X. It was mentioned in an answer to this question as well, but back then I did not understand the issue. The thing is that in my case $^X contains the actual path to the perl executable where it is located when the script is running, while $Config{perlpath} contains the path to the perl executable when it was compiled.

I compiled and originally installed this perl to the /home/dwimperl/dwimperl-linux-5.20.1-1-x86_64/perl/ directory, but when Travis-CI uses it, it is placed to /home/travis/dwimperl-linux-5.20.1-4-x86_64/perl/.

Changing the test

One solution would be to send a patch to the maintainers of Test::Differences to use $^X instead of $Config{perlpath}, but I am not sure they'd accept, I don't know if this would be right to do, and most importantly, this would only solve this specific case. Surely there are going to be other modules using $Config{perlpath} and they'd be broken as well. Even the real users of DWIM Perl for Linux might us that value and the system will be broken for them.

Skip the test

Another solution would be to install Test::Differences using the --notest flag of cpanm. This solution would be quicker (no need to wait for the maintainers of Test::Differences), and no need to depend on them, whether they accept the change or not. On the other hand this would not solve any of my other concerns. This could be a work-around till I find a better solution.

Change $Config{perlpath}

DWIM Perl is supposed to be relocatable. It was compiled with the userelocatableinc flag which means it automatically adjusts the content of @INC to the location of perl. That part worked well. I wonder if there is some other flag I need to use to compile perl to make it adjust perlpath and maybe even some other variables?

Running perl -MData::Dumper -MConfig -e'print Dumper \%Config' shows quite a few variables that contains the full path to where this perl was first installed. There are quite a few that show the new path but these variables include the old one, that does not exists any more: 

config_arg3
config_args
initialinstalllocation
installbin
installprefix
perlpath
startperl

As I can see this thread on the Perl 5 Porters list was about a solution for this problem.

I posted this question on Perl Monks as well.