Fellow Monks,
thanks to your help (see Maybe Escape in Dynamic RegExps) I have been happy for quite while but now the fun is continued.

my $e = '\\'   # kind of escape char
my $s = '\'';  # this is a string to use for splitting
if(string_contains_newlines()) {
  $s .= "\n"; # ?? right so?  
}
my $re = "(?<!\Q$e\E)\Q$s\E";
$split_re = qr/$re/s;
[download]

That is to say: when the string to split contains newlines (or --more precisely-- $/) I need to split the string according to a new regular expression that takes the former separator (stored in $s here) plus the newline character(s).

As you might guess, the above code doesn't work and I've run out of ideas what else to try.

Any hints or help appreciated.