Recent updates (in June 2012) to Arch Linux replaced Perl 5.14 with 5.16.

Imagine my surprise when Perl scripts (including cpanp) suddenly stopped working.

I asked about the problem on PerlMongers and the Arch Linux forum, and did the following to solve it:

• Delete all files under /usr/bin/site_perl, /usr/lib/perl5/site_perl and /usr/share/perl5/site_perl to remove the duplicates installed by the cpan shell.
• Rebuild all AUR packages that contain perl XS modules. This will print them out:

  sudo pacman -Qml | awk '/_perl/auto/.+.so$/ { print $1 }' | uniq

  (There weren't any on my system.)

• Reinstall perl-cpanplus-dist-arch
• Run cpanp to install the Perl modules that aren't available on Arch or AUR, for example:

  sudo cpanp -i Math::Combinatorics

Which seems to have done the job.