If you're trying to make sure a script only runs under a specific (or later) version, there is always:

use strict;
use warnings;
require 5.8.1;
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And if you don't want that to be fatal, you can do this:

use strict;
use warnings;
eval "require 5.8.1;";
if ( $@ ) {
    print "Nice try!\n$@";
} else {
    print "Thanks for not asking to run me under Perl 4.\n";
}
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