One way would be to add your private module path before the CPAN module path in @INC so that Perl will prefer local module installations over installations from CPAN:

BEGIN {
    my $private_module_path = '/usr/local/myscript/lib';
    unshift @INC, $private_module_path;
};
use Net::MyModule; # will pick up the first Net/MyModule.pm that is fo
+und in @INC
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An alternative approach would be to load both modules and then try to find out which one has the largert version number, but that is a hairy thing to try and a user who does local modifications might not think of bumping the version number high enough.