use strict;
use warnings;
use lib 'lib';

my $arg = shift // ''; 

if ($arg eq "load") {
  print "Now loading optional library.\n";
  require Foo;
  my $o = Foo->new;
  # Do stuff with $o here..
}
else {
  print "I skipped loading the optional library.\n";
  print "Try passing the 'load' option to load it.\n";
}