use Benchmark qw(cmpthese);


fbard@devo1:~/spot_camp_layout$ cat rindex 
use Benchmark qw(cmpthese);

my $x = ("x" x 100_000)."</body></html>"; 
my $lc_x = lc($x);
my $end_html = qr{(</body></html>)};

cmpthese(100_000,{
    rindex_substr => sub{
     my $str = $x;
     substr($str,rindex($lc_x,"</body>"),0,"yyyy"); 
    },
    regex => sub{
     my $str = $x;
     $str =~ s|$end_html$|yyyy$1|i;
    }
});

                 Rate         regex rindex_substr
regex         18416/s            --          -75%
rindex_substr 73529/s          299%            --