DynaLoader seeing wrong values in @INC

Question

I have multiple versions of Perl installed; each under a different directory. e.g. C:\Perl\5.x.y. I switch between them in a shell by setting PERL5LIB and altering my PATH so that only one version is visible at a time. Normally, this works fine, but when trying to run the version of pp (PAR::Packer) installed under 5.10.1 I have problems loading XS components. parll2nc.exe complains:

This application has failed to start because perl512.dll was not found...

I set PERL_DL_DEBUG and see the following when DynaLoader initializes:

DynaLoader.pm loaded (C:/Perl/5.10.1/site/lib C:/Perl/5.12.1/lib ., \lib)

The stuff before the comma is @INC. The first entry is correct, the second is not. I can't figure out how DynaLoader is getting a 5.12 lib path as running perl directly shows what I would expect:

C:\>perl -e "print join ' ', @INC"
C:/Perl/5.10.1/site/lib C:/Perl/5.10.1/lib .

How is DynaLoader picking up the wrong path and how do I prevent it from doing so?

Answer 1

Similar to the approach I suggested for this question, put a trace on @INC and see when it gets updated.

At the very top of your script, before any other use statements, put:

use Tie::Trace;
BEGIN { Tie::Trace::watch @INC };

Then you will get a warning message when another module edits your @INC array.

Answer 2

I figured it out. The problem is caused by an interaction of several things:

• I have *.pl files associated with perl.exe (for the most recent version of Perl installed -- 5.12.1).
• I have ".PL" in my PATHEXT environment variable so that I can run Perl scripts without typing the extension. e.g. C:\>foo instead of C:\>foo.pl
• My installation of the pp utility does not have a batch file wrapper created with pl2bat. (I'm not sure why.)

The net result is that when I ran pp @myconfig it effectively did this:

C:\Perl\5.12.1\bin\perl.exe C:\Perl\5.10.1\site\bin\pp.pl @myconfig

i.e. it ran the version of pp.pl in my path using the version of perl associated with *.pl files, not the version of perl in my PATH. Thus the mix of libs in @INC between what came from the executable (C:\Perl\5.12.1\lib) and what came from the PERL5LIB environment variable (C:\Perl\5.10.1\site\lib).

The solution is to either run pp as perl pp.pl or (better, because you don't have to remember anything) to create a batch wrapper. Assuming that .BAT is in PATHEXT before .PL, when you type pp Windows will run pp.bat instead of pp.pl, and pp.bat invokes perl (using the version in your path).

sigh