Perl on Mac OS 10.10 Yosemite with strange @INC path

Question

After upgrading to OS 10.10 I had to install all former used perl modules again. No problem. I thought.

Perl on OS 10.10 is "This is perl 5, version 16, subversion 3 (v5.16.3) built for darwin-thread-multi-2level" (from perl --version). The @INC looks to be (try perl -e 'print join("\n", @INC);' or perl -V):

/opt/local/lib/perl5/site_perl/5.16.3/darwin-thread-multi-2level /opt/local/lib/perl5/site_perl/5.16.3 /opt/local/lib/perl5/vendor_perl/5.16.3/darwin-thread-multi-2level /opt/local/lib/perl5/vendor_perl/5.16.3 /opt/local/lib/perl5/5.16.3/darwin-thread-multi-2level /opt/local/lib/perl5/5.16.3 /opt/local/lib/perl5/site_perl /opt/local/lib/perl5/vendor_perl

When I try to use an unknown module, perl throws: "Can't locate Mymodule.pm in @INC ... and then: @INC contains: ... /Library/Perl/5.18/darwin-thread-multi-2level /Library/Perl/5.18 /Network/Library/Perl/5.18/darwin-thread-multi-2level /Network/Library/Perl/5.18 and all other known (and added 5.18 perl.pm folders). Every perl dev knows that message. But read literally: @INC links obviously to 5.18 folders ! And at a first glance I supposed to use Perl 5.18.

I installed my first bunch of new modules from Macports. 5.18 portfiles. And added the new module pathes to the list /Library/Perl/5.18/AppendToPath. Worked well. But when I installed a module - not available as 5.18 in Macports - with cpan, I got trouble. The module was compiled with 5.16 (of course, see above) and was not accepted as other path in the AppendToPath file. Dynaloader mismatch.

I do not know, where the @INC list is altered at runtime. In earlier Mac OS 10 versions, the new @INC included same version module versions. I.e. an active perl 5.14 included also 5.14 modules, 5.12 included 5.12 pathes a.s.o. Why does perl 5.16 on Yosemite include 5.18 module pathes ?

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To add some confusion after my post: When I try a print $^V in program code, I get 5.18. That means, you don't get what you meant to get. May be my shebang #!/usr/bin/perl starts 5.18 and not 5.16.

Answer 1

Experienced Perl developers will tell you to ignore the system perl. If you upgrade it, for a bugfix you need, you run the risk of breaking your OS. If you upgrade your OS, a modified system perl may break your code.

Macports and homebrew are both great, but not ideal for Perl. I'd clear the /opt/local/version from my PATH, or even my system.

Do yourself a big favor. Install Xcode with the Command Line Tools. Install perlbrew. Roll up your own perl. Heck, roll up 6 of your own perls and jump back and forth between them. Keep a threaded version around for when you need it. Keep a non-threaded around for speed. Best of all, whenever you change which version you are using, perlbrew updates your environment correctly for you. No fuss, No muss.

Answer 2

Solved

OS Yosemite as an update from Maverick provides perl 5.16 and 5.18. When testing which perlyou will get /opt/local/bin/perl, which is a symlink to /opt/local/bin/perl5.16.

When you use #!/usr/bin/perlas standard shebang in perl programs (portable i.e. to Linux), you will run this program with another perl version, because #!/usr/bin/perl really exists as a binary with version 5.18.

When you use cpan / cpanm (cpanminus) for easy and quick installation of new modules, you'll get the modules compiled as 5.16 versions. Because this is assumed as standard path / version (see above).

You will find cpanm at /opt/local/libexec/perl5.16/sitebin/ You also will find /opt/local/libexec/perl5.18/ but no sitebin and no cpanm.

And now: Create a folder sitebin in /opt/local/libexec/perl5.18/ and copy the file /opt/local/libexec/perl5.16/sitebin/cpanm to /opt/local/libexec/perl5.18/sitebin/ (use sudo ... to get permissions).

cpanm is a normal perl program file, independent from versions - but watch the shebang of this file! Open the file and edit the first two lines from

#!/opt/local/bin/perl5.16 
eval 'exec /opt/local/bin/perl5.16  -S $0 ${1+"$@"}'

to

#!/opt/local/bin/perl5.18 
eval 'exec /opt/local/bin/perl5.18  -S $0 ${1+"$@"}'

that means: simply change 5.16 to 5.18. That's all.

Now you are able to install new modules with this new cpanm. The new cpanm will deploy the modules in /opt/local/lib/perl5/site_perl/5.18/darwin-thread-multi-2level/. To let the new path know to perl 5.18 on Mac edit the file /Library/perl/5.18/AppendToPath and append a new line with /opt/local/lib/perl5/site_perl/5.18/darwin-thread-multi-2level (without slash at the end).

That's it.