Maybe you already know that if you want to match a whitespace character except '\n', you could use the [^\S\n] idiom. Where \S matches any non-white space character, \n matches the return, and then take the complement of the set gives you \s but not \n. Handy trick in situations when you want to differentiate between whitespace and \n.
And you get -my $text = 'hello this is a multiline message'; $text =~ s/([^\S\n]+|\n)/$1 eq "\n" ? print "New line\n" : print "Whitespaces\n"; $1/gemi;
New line Whitespaces Whitespaces Whitespaces Whitespaces New line Whitespaces