To add on to the suggestions above, I would also put it all in a BEGIN block.

#!/usr/bin/perl
use strict;
use warnings;
use vars qw( $ne_loaded );
                                                                      
+                                                          
BEGIN {
  eval "use Non::Existent";
  if ($@) {
      warn "You don't have Non::Existent installed so...";
    $ne_loaded = 0;
  }
}
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