output.txt

[sweeks@kweh ~]$ perl slasho.pl
             Rate without    with
without 1468429/s      --     -4%
with    1536098/s      5%      --

slasho.pl

#!/usr/bin/perl

use Benchmark qw(:all :hireswallclock);

my $var = 'text';
cmpthese( 10000000, {
    without => sub {
        my $x = 'omg text lol';
        $x =~ s/$var/wtf/;
    },
    with => sub {
        my $x = 'omg text lol';
        $x =~ s/$var/wtf/o;
    },
});