Dedicated monks!

I'm in search of wisdom regarding perlbrew, specifically about controlling where perlbrew installs architecture-specific (i.e. compiled) modules.

I have installed perlbrew in standard fashion, used it to install a few versions of perl, and then installed some modules. But my architecture-specific files are going to a common tree, leading to this type of error: 

$ which perl
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/bin/perl
perl -M JSON::XS -e 1
Perl API version v5.14.0 of JSON::XS does not match v5.16.0 at /home/j
+roth/perl5/perlbrew/perls/perl-5.16.3/lib/5.16.3/XSLoader.pm line 92.
Compilation failed in require.
BEGIN failed--compilation aborted.

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Where did JSON::XS get installed? 
 find /home/jroth/perl5 -name XS.pm | grep JSON
/home/jroth/perl5/lib/perl5/x86_64-linux/JSON/XS.pm

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A shared directory! And where is my current perl looking for modules? 
perl -E 'say join $/, @INC'
/home/jroth/perl5/lib/perl5/x86_64-linux-gnu-thread-multi
/home/jroth/perl5/lib/perl5/x86_64-linux
/home/jroth/perl5/lib/perl5
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/x86_
+64-linux
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/5.16.3/x86_64-linux
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/5.16.3

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Does my environment have anything to do with this? 
env | grep -i perl5lib
PERL5LIB=/home/jroth/perl5/lib/perl5/x86_64-linux-gnu-thread-multi:/ho
+me/jroth/perl5/lib/perl5

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Did I do that? 
grep -i perl5lib ~/.bashrc ~/.bash_profile
(n/t)

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It appears I have two problems:

1. Under perlbrew, CPAN clients install architecture-specific files in a common tree, i.e. 

/home/jroth/perl5/lib/perl5/x86_64-linux-gnu-thread-multi
/home/jroth/perl5/lib/perl5/x86_64-linux

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even though these compiled files are most certainly incompatible across perl versions.

2. Under perlbrew, perl looks for architecture-specific files in a common tree, even though there are appropriate directories specific to each version of perl, i.e. one of 

/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/x86_
+64-linux
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/5.16.3/x86_64-linux
/home/jroth/perl5/perlbrew/perls/perl-5.16.3/lib/5.16.3

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My questions are then, how to to set the preferences for a CPAN client under perlbrew to install to the latter set of directories (whether arguments, environment settings or patches?)

And similarly, to remove the former architecture-specific-shared directories from the PERL5LIB environment variable.

I'm confused that with perlbrew being around so long and having such a good reputation, no else seems to have this fundamental complaint and no bug has been filed against perlbrew on this issue.

Well there is a question at stackoverflow How can Install multiple Perl versions without them tripping over each other's XS modules? although the only answer is brian d foy's "don't use perlbrew, give each perl binary a version, i.e. perl-5.16.3 and let them find their own installed modules".

And there is Kent NL's post, although I didn't find it helpful, as cpanm clients continued installed to the shared tree, even after installing cpanm for each perl version.

Thanks for your interest and support!

UPDATE: For reasons unclear, my PERL5LIB environment variable is no longer set, and perlbrew is now behaving properly. I think it's possible that one of the terminals I was working had retained environment settings from local::lib, even after I had cleaned out those settings from .bashrc.

UPDATE 2: I've filed a bug against perlbrew, suggesting a warning on detecting any non-null PERL5LIB setting.

In reply to Architecture-specific module conflicts under perlbrew by gnosti

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