Yes, of course :-) do updates %INC, and a subsequent require will just return 1, telling that the file has already been loaded. This is actually a feature, it is a conditional do. 

$ echo 13 > lucky.pl
$ perl -l
print do 'lucky.pl';
if (1 == require 'lucky.pl') {
    print "already loaded.";
    delete $INC{"lucky.pl"};
}
print require 'lucky.pl';
print do 'lucky.pl';
__END__
13
already loaded.
13
13

[download]

update: updated code with conditional block

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'

In reply to Re^6: XML::Twig Support for Parameter Entities (%INC) by shmem
in thread XML::Twig Support for Parameter Entities by dtdattacks

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