#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use feature 'say';
# use Benchmark qw(:all) ; # WindowsOS
use Benchmark::Forking qw( timethese cmpthese ); # UnixOS

sub getn_unpack {
    return unpack "x" . ($_[1]-1) . "a", $_[0];
}

sub getn_substr {
    return substr $_[0], $_[1]-1, 1;
}

sub getn_split {
    return +(split //, $_[0])[$_[1]-1];
}

my $strNum = "12345678910";
my $string = "ACATCACCTCCCACAACGAGGACTACACCATCGTGGAACA";

# say getn_unpack($string, 10);
# say getn_substr($string, 10);
# say getn_split($string, 10);

my $results = timethese(1000000000, { 'unpack' => getn_unpack($string, 10),
					  'substr' => getn_substr($string, 10),
					  'split' => getn_split($string, 10),
			}, 'none');
cmpthese( $results );

__END__

$ perl test.pl
              Rate unpack substr  split
unpack 171232877/s     --   -23%   -31%
substr 223713647/s    31%     --   -10%
split  248138958/s    45%    11%     --