In another response, grinder scrutinized your problem solution and offered a more efficient solution based on the index() function without any regular expressions.

I personally believe that the claim about efficiency is not correct, since that kind of regex should get optimized to index anyway - and often regexen have a more immediately readable syntax. For a Perl programmer that is...

I hope that the following minimal benchmark can shed some light:

#!/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__

[download]

I get e.g.

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

[download]

and

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

[download]

on two different systems.

Now, is this test flawed? I easily tend to get these kinda things wrong, I must admit...

In reply to Re^2: Regex for Differentiating Underscore and Whitespace by blazar
in thread Regex for Differentiating Underscore and Whitespace by neversaint

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