#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw/cmpthese :hireswallclock/;

my @a = do {
    my @chr=(grep /\w/, map chr, 1..255);
    map { 
        local $_ = join '', map $chr[rand @chr], 1..1000;
        tr/_/ / if .5<rand;
        $_;
    } 1..1000;
};

cmpthese 5000 => { Regex => sub () { grep !/_/, @a },
                   Index => sub () { grep index($_, '_') < 0, @a } };

__END__

##</code><code>##

C:\temp>perl index.pl
       Rate Index Regex
Index 891/s    --   -0%
Regex 891/s    0%    --

##</code><code>##

blazar@perlmonk ~ $ perl index.pl
       Rate Index Regex
Index 261/s    --   -0%
Regex 262/s    0%    --