From: Ryan Tarpine <rtarpine@...>
Date: 2001-08-31T01:44:46+09:00
Subject: [ruby-talk:20586] Re: Relative path

Renaud HEBERT wrote:

> <snip>
> ...
> But:
> 1) it is still very fragile: 'dir//dir2' and 'dir/./dir2' will give
> wrong results when compared to 'dir/dir2'
> 2) unix is case sensitive, windows is not; '/' vs '\'..
> 3) it should be possible to do it only with strings manipulation to be
> more efficient..

def rel_path(a, b)
  # Should work in in win and *nix
  sep = File::Separator

  # Get rid of /path//to/./here problems
  a = (File::expand_path a).split(sep)
  b = (File::expand_path b).split(sep)

  # Windows?
  raise "can't switch drives" if a[0] =~ /^\w\:$/ and a[0] != b[0]

  # If one of the paths starts with /, the split array
  # will have an empty first element (if a path is solely
  # /, it will be empty)
  a.shift unless a.empty? or not a[0].empty?
  b.shift unless b.empty? or not b[0].empty?

  # If a & b are empty, a[0] == b[0] == nil
  while a[0] == b[0] and not a.empty? and not b.empty?
    a.shift
    b.shift
  end

  parent = ".." + sep
  (parent * a.size) + b.join(sep)
end

I'm not sure about your last one, but I do have a problem of my own.
What about network drives?  e.g. //server/myservice  File::expand_path
on a string beginning with multiple "/"'s will not squeeze them into one 
"/".  I assume this is not to mangle network paths.  I have abolutely no 
experience with them, so I don't know if you just raise an exception.  
Someone else should have no problem answering this.  

Also:  "/".split("/").length == 0, but "/a".split("/a").length == 2.  In 
the second one, there is an empty string for the first element.  Should the 
first one act the same (return an array with a single element, an empty 
string)?

-- 
Ryan Tarpine, rtarpine@hotmail.com
"Technology is a queer thing.  It brings you great gifts
in one hand, and it stabs you in the back with the other."
         -- C.P. Snow