That doesn't work. The mere existence of those variables anywhere in your code will trigger this problem. The following will demonstrate the problem:

use Benchmark;
                                                                      
+          
my $text = <<'END_TEXT';
    this
  isa
 test    of test text
        that I am
  testing
END_TEXT
                                                                      
+          
my $start = new Benchmark;
                                                                      
+          
for (1 .. 1000000) {
    while ($text =~ /(test)/g) {
        my $foo = $1;
    }
}
my $end = new Benchmark;
my $diff = timediff($end, $start);
print "While not using \$` the code took: ",timestr($diff),"\n";
exit;
my $foo = $`;
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Run that a few times, then try commenting out that last line. Even though that line can never be executed, you'll see that the presense of that variable slows the program down.