As a lowly acolyte I have great respect for <kbd>map</kbd> and a fondness of good old <kbd>foreach</kbd>. So I naturally thought: isn't a loop with simple pattens faster than a pattern with <kbd>|</kbd> in it?

Here's my benchmarking code:

use Benchmark;

timethese(500, {
        'or pattern'    => \&orpattern,
        'many patterns' => \&manypatterns
});


sub init {
   %sub_hash = (John => Mike, Jack => Mark, Joe => Moe);
   $string = "Dear John!.\nI've run off with Jack and Joe.\nSue\n\n"
               x 1000;
}


sub orpattern {
        init;

        my $keys = join '|', map "\Q$_\E", keys %sub_hash;
        my $keys_REx = qr/$keys/;

        $string =~ s/($keys_REx)/$sub_hash{$1}/g;
        return $string;
}

sub manypatterns {
        init;

        my %patterns = map { qr/$_/ => $sub_hash{$_} } 
              keys %sub_hash;

        foreach $pat (keys %patterns) {
                my $replace = $patterns{$pat};
                $string =~ s/$pat/$replace/g;
        }
        return $string;
}
[download]

And the results:

Benchmark: timing 500 iterations of many patterns, or pattern...
many patterns:  2 wallclock secs ( 1.61 usr +  0.00 sys =  1.61 CPU)
or pattern: 12 wallclock secs (11.94 usr +  0.01 sys = 11.95 CPU)

Of course there's a difference in functionality between the two, just think of:

%substitute_hash = ( Jack => Chris,  Chris => Jaquline );
[download]

--
Brigitte    'I never met a chocolate I didnt like'    Jellinek
http://www.horus.com/~bjelli/         http://perlwelt.horus.at