in reply to Different behaviors between "while" and "map"
The reason this happens is because the while loop is designed to operate on <> like an iterator. Thus, it reads one line at a time until it can't read anymore.
By contrast, using <> as the list for your map block reads the entire file in all at once, incrementing $. along the way. The entire file then gets passed to your map block as one big list, and by this time, $. has already been incremented to the number of the last line, so the same $. gets printed each time through the map block.