I bet you meant to say you don't understand why this is. Just in case: it's because the return value of /(.+)\./ in case of a match is a list with a single element: The item matched between the parentheses.

On the other hand, the return value of /(.+)\./ . "\n" is "1\n" because the dot puts the regex in scalar context, in which case it returns true (1) or false ("").

You could work around it by putting a map { "$_\n" } in front of your map.