print map { "$prefix$_" } split /\n/, join '', @_

Fixed:

print map { "$prefix$_" } split /^/m, join('', @_), -1;
[download]

Note: split implies the "m" for that pattern, but it's clearer to specify it.

Update: As Eliya kinda points out, there won't ever be null trailing fields with that pattern, so the above can be simplified to

print map { "$prefix$_" } split /^/m, join '', @_;
[download]

Great solution! I completely forgot about the "negativ LIMIT" parameter of split.
-- 
Ronald Fischer <ynnor@mm.st>

I completely forgot about the "negativ LIMIT" parameter

I think the crucial idea here is to split on ^, not the negative limit. The latter isn't even needed, because there are no null fields in this case.

The first solution is not correct, because it would drop the newline characters. The second solution keeps most newline characters, but if the string contains a sequence of \n, all but the first are ignored...