"The empty string between two spaces" is a funny wording. All I mean is that between any two neighbouring chars, you can say there is any number of zero-length strings ($a = '1'; $b = '2'; $empty = ''; $c = "$a$empty$b"; then $c eq "$a$b" and $c eq "$a$empty$b" and $c eq "$a$empty$empty$b" ...). I am aware that when using perl to extract zero length character sequences using split or regular expressions, it returns undef.