This is an easy one. It falls into the category of obfuscation that I like best: the use of simple or surprising features. In that respect there is only one feature in this code and it may be obvious or it may not be.

With the cloaking devices turned off the code looks like this:

    $_ = "Some string here";

    s/.*//;

    s//$&Just /;
    s//$&Another /;
    s//$&Perl /;
    s//$&Hacker\n/;

    print;
[download]

The trick in this code is highlighted by the question; what pattern is matched in the last four s///'s?

--
John.