(1) The base-definition of "@INC" is specified at compile-time when 'perl' itself is built. Some "distros" put site_perl first; others (like Gentoo) put vendor_perl first. (2) CPAN's install-behavior is determined by one of its "o conf" settings; PREFIX is usually the best. (3) Beyond that, the PERL5LIB environment-var puts things at the front of @INC. I resigned myself quite some time ago to specifying PERL5LIB in either a user-specific or site-wide login script, setting CPAN appropriately (in a non-root "maintenance" account used for such things), and installing "my stuff" into a user-specific or site-local location of my choosing. Since my OS (Gentoo) drives most of "its" stuff using Perl, and using its own methodologies to do so, this keeps "their" stuff mostly unaware of "my" stuff.