use Benchmark;
    use vars qw/$a $b $c/;
    ($a, $b, $c) = qw/bar baz foo/;

    timethese(shift || 500000, {
        lookbehind => sub { local $_ = "foobarquux"; s/(?<=$c)$a/$b/g },
        chromatic  => sub { local $_ = "foobarquux"; s/($c)$a/$1$b/g  },
        chromatic2 => sub { local $_ = "foobarquux"; s/$c$a/$c$b/g  },
        substr     => sub {
            local $_ = "foobarquux";
            while ((my $p = index($_, "$c$a"))>=0) {
                substr($_, $p+length($c), length($a), $b);
            }
        },
    });

##</code><code>##

 chromatic: 11 wallclock secs (10.67 usr +  0.00 sys = 10.67 CPU) @ 46860.36/s (n=500000)
chromatic2: 10 wallclock secs ( 8.81 usr +  0.00 sys =  8.81 CPU) @ 56753.69/s (n=500000)
lookbehind: 10 wallclock secs ( 9.42 usr +  0.00 sys =  9.42 CPU) @ 53078.56/s (n=500000)
    substr:  4 wallclock secs ( 3.98 usr +  0.00 sys =  3.98 CPU) @ 125628.14/s (n=500000)