a) changing @INC at runtime won't work for modules (subsequent evals or requires will see the change, but not any uses); b) what you've done in no way modifies @INC for any subsequent invocations of perl. If you want to permanently modify it you need to set PERL5LIB in the environment, use the -I command line switch each time, or recompile perl. See perldoc lib and perldoc perlrun and read carefully.