#!/usr/bin/perl
use Benchmark qw(cmpthese);

my $test_text = q|Wow, that was quick!<br/>
Two points:<br/>
1) I only  want space, not tabs or new lines - so shouldn't the \s be   replaced with " "? <br/>
2) Is there  a difference between inkgmi's and GrandFather's entry? <br/>
PS I thought executed regexs are experimental (so says the man page) - is there a problem   with them?<br/>
|;
my $working_var;
my $count = 1000000;

cmpthese($count, {
    'grandfather' => sub {$working_var = $test_text; $working_var =~ s/ ( +)/" " . ("&nbsp;" x length ($1))/ge},
    'ikegami'     => sub {$working_var = $test_text; $working_var =~ s/(?<= )( )/'&nbsp;' x length($1)/eg}
});

__OUTPUT__
Benchmark: timing 1000000 iterations of grandfather, ikegami...
grandfather: 31 wallclock secs (31.01 usr +  0.00 sys = 31.01 CPU) @ 32252.86/s (n=1000000)
   ikegami: 52 wallclock secs (51.26 usr +  0.00 sys = 51.26 CPU) @ 19506.87/s (n=1000000)
               Rate     ikegami grandfather
ikegami     19507/s          --        -40%
grandfather 32253/s         65%          --