use strict;
use warnings;

use Benchmark 'cmpthese';

my $sz      = ( shift || 10 ) - 4;
my $X = 'N' . 'x' x $sz . '000';
my $Y = 'N' . 'x' x $sz . '001';

cmpthese( 1,
          {
           '?!X'  => 'use strict; $X =~ /^N(?!.*00$).*$/',
           '?!Y'  => 'use strict; $Y =~ /^N(?!.*00$).*$/',
           '?<!X' => 'use strict; $X =~ /^N.*(?<!00$)$/',
           '?<!Y' => 'use strict; $Y =~ /^N.*(?<!00$)$/',
           }
        );


__END__
Benchmark: timing 1 iterations of ?!X, ?!Y, ?<!X, ?<!Y...
runloop unable to compile 'use strict; $X =~ /^N(?!.*00$).*$/': Global symbol "$X" requires explicit package name at (eval 2) line 1.

code: sub { for (1 .. 1) { local $_; package main; use strict; $X =~ /^N(?!.*00$).*$/;} }