use strict;
use warnings;
use re 'eval';

STDOUT-> autoflush( 1 );

use constant LEN => 10_000;

my $n = 0;
my $s = '1' x LEN;;
my $r = '(1)(?{ 

#    $^N ? 1 : 1;        # (*) does use of $^N exacerbate?

    print "*" and select            # to better watch
        undef, undef, undef, 0.25   # with htop
            unless ++ $n % 1000     #
})' x LEN;

print "\nMatch\n" if $s =~ /^$r$/;
print "1) Hit Enter"; <>;

( $s = '' ) =~ //;              # reset everything 
                                # about $s and re-engine (?)

$s = ( int rand 10 ) x 1e9;     # allocate another Gb
print "2) Hit Enter"; <>;