But this of course fails if someone happens to do

BEGIN { unshift @INC, sub { ... } }

use lib 'somewhere/special';
require Net::Ping; # Resolves to "somewhere/special/Net/Ping.pm".
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as lib also unshifts @INC. This accident may not be obvious if it's a module that uses lib.

For many purposes it works, but one should be aware of that it's not bullet proof against accidents.

lodin