# /tmp/foobar/Foo.pm
package Foo;

!! 'keep require happy';

sub baz {
  print 'Hello from ' . shift() . '::baz' . "\n";
}

__END__

##</code><code>##

# ./Bar.pm
package Bar;
use base 'Foo';

!! 'keep require happy';

__END__

##</code><code>##

# ./my_script.pl
use lib '/tmp/foobar';
use Bar;

Bar->baz();

__END__

##</code><code>##

% perl my_script.pl
Hello from Bar::baz

##</code><code>##

% perl -I/tmp/foobar my_script.pl

##</code><code>##

% perl -Mlib=/tmp/foobar my_script.pl