Right argument, japhy!! But it's an interesting problem nevertheless. Your regex breaks on: New York/York/Boston => New York/Boston My fix makes it sadly less elegant:

    1 while s{
      (/|^)   # add: capture slash or start of string: $1
      ([^/]+)      # non-slashes (the city): \2
      /            # a /
      (?=          # look ahead for:...
        (?:        # group (not capture)
          [^/]* /  # city and /
        )*?        # 0 or more times, non-greedily
        \2         # is the city here again?
        (?: /|$ )  # a / or end-of-string
      )
    }
    {$1}gx;  # add: replacement
[download]

Now this is close to my approach:  1 while s#(/|^)((?>[^/]*))/(?=(?:.*?/)?\2(?:/|$))#$1#g; The advantage of both solutions is that as little as possible is replaced. The disadvantage is that a regex isn't the right way to do it ;) - for all the reasons already given in this thread.

-- Hofmator