What you need is this:
$info = "one;two;three;four;five;six;"
@items = split(/;/, $info);
$extract = @items[3] + @items[4];
Now extract should contain the string "fourfive".
Arrays in perl are normally zero based, but I think there was something
to change that if you really needed it.
(Sorry I didn't do any Perl for quite some time now. :) )
Cheers
Manfred