#!/usr/bin/perl
use warnings;
use strict;

use Test::More;
use Benchmark qw{ cmpthese };

sub regex {
    my ($string, $find, $replace) = @_;
    $string =~ s/\Q$find/$replace/g;
    $string
}

sub substring {
    my ($string, $find, $replace) = @_;
    my $length = length $find;
    my $pos = 0;
    while (-1 != ( $pos = index $string, $find, $pos )) {
        substr $string, $pos, $length, $replace;
    }
    $string
}

sub array {
    my ($string, $find, $replace) = @_;
    join $replace, split /\Q$find/, $string, -1
}

my @args = ('12a345a678a90', 'a', '||');
is regex(@args), '12||345||678||90', 'manual';

for my $args (\@args,
              [ '123456789abcdefghijkl' x 1000,
                '123456789abcdefghijkl' x 21,
                'ABCDEFGH'
              ]) {
    is regex(@$args), substring(@$args), 'regex - substring';
    is substring(@$args), array(@$args), 'substring - array';

    cmpthese(-3,
             { regex     => sub { regex(@$args) },
               substring => sub { substring(@$args) },
               array     => sub { array(@$args) },
           });
}
done_testing(5);
[download]

Output on my machine (Perl 5.20.1, Linux on Intel i3):

ok 1 - manual
ok 2 - regex - substring
ok 3 - substring - array
              Rate     regex substring     array
regex     313491/s        --      -21%      -36%
substring 398041/s       27%        --      -19%
array     488419/s       56%       23%        --
ok 4 - regex - substring
ok 5 - substring - array
             Rate substring     array     regex
substring 18505/s        --      -15%      -15%
array     21765/s       18%        --       -0%
regex     21765/s       18%        0%        --
1..5
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]