split is slow. However, if you want just the first character of the string (I often do), then you can significantly speed up split by giving it the value 2 as LIMIT argument.

Benchmarked code from above (obviously on a faster machine) with 1 million iterations:

     split: 17 wallclock secs (16.69 usr +  0.02 sys = 16.71 CPU) @ 59
+844.40/s (n=1000000)
    substr:  0 wallclock secs ( 0.74 usr +  0.00 sys =  0.74 CPU) @ 13
+51351.35/s (n=1000000)
    unpack:  1 wallclock secs ( 1.02 usr +  0.00 sys =  1.02 CPU) @ 98
+0392.16/s (n=1000000)
[download]

     split:  2 wallclock secs ( 1.16 usr +  0.00 sys =  1.16 CPU) @ 86
+2068.97/s (n=1000000)
    substr:  1 wallclock secs ( 0.70 usr +  0.00 sys =  0.70 CPU) @ 14
+28571.43/s (n=1000000)
    unpack:  0 wallclock secs ( 0.96 usr +  0.00 sys =  0.96 CPU) @ 10
+41666.67/s (n=1000000)
[download]

#!/usr/bin/perl -w
use strict;

use Benchmark;

use vars qw/$str/;

$str = "123456789asgdjlaskjglkajblnlbnlaqjteoijqotijwojgl;akjglkj";

timethese(shift || 1000000, {
    'unpack' => sub { my $char = getn_unpack($str, 1) },
    'substr' => sub { my $char = getn_substr($str, 1) },
    'split'  => sub { my $char = getn_split($str, 1) }
});

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

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

sub getn_split {
    return +(split //, $_[0],2)[$_[1]-1];
}
[download]

Still slower than the other solutions, but nevertheless a speedup of over 10 to an unrestricted split. See if using the LIMIT argument in split would help your code.