#!/usr/bin/perl -w
use strict;
use Benchmark qw[ cmpthese timethese];

my $string='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa';
my @chars=split //,$string;

cmpthese 
(  1000000, 
 {
   'Substr'=>sub
   {
      my $string='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa';
      for (my $i=0;$i<length $string; $i++) 
      {
         my $char=substr $string,$i,1;
      }
    },
    'pre_splitted'=>sub
    {
         foreach my $char (@chars) {}
    },
     'Split'=>sub
    {
	my @string=split //,'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa';
	foreach my $char (@string) {}
     },
     'Shift'=>sub
     {
         my @string='aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa';
	 shift @string;{}
      }
  }
);
__END__
prints:
                 Rate   Split   Substr pre_splitted   Shift
Split          8840/s    --      -72%     -94%        -99%
Substr        31465/s   256%      --      -78%        -95%
pre_splitted 140667/s   1491%     347%     --         -80%
Shift        695410/s   7767%    2110%    394%         --