Wow, I learn something new about perl every day.

from perlvar:

    After a match against some variable $var:

$` is the same as substr($var, 0, $-[0])
$& is the same as substr($var, $-[0], $+[0] - $-[0])
$' is the same as substr($var, $+[0])
$1 is the same as substr($var, $-[1], $+[1] - $-[1])
$2 is the same as substr($var, $-[2], $+[2] - $-[2])
$3 is the same as substr $var, $-[3], $+[3] - $-[3])
[download]

so I wrote a test case:

use strict;
for    my $regex (qr/(.)oo(.)ar(.)az/, qr/fo(.)barba(.)/) {
    my $str = "foobarbaz";
    $str =~ s/$regex/
        my @a;
        for my $index (1 .. $#+) {
            push @a, substr($str, $-[$index], $+[$index] - $-[$index])
+;
        }
        join "," , @a;
    /e;
    print "$str\n";
}
[download]

outputs

f,b,b
o,z
[download]

I'll have to remmember that one.