El Capitan SIP and CPAN
Solution 1:
You can install a newer version of cpan in /usr/local/bin with the following CPAN configuration:
cpan
cpan> o conf makepl_arg "INSTALLBIN=/usr/local/bin INSTALLSCRIPT=/usr/local/bin"
cpan> o conf commit
cpan> exit
sudo cpan -i CPAN
This solution, and others, is discussed at perlmonks.