From: Pit Capitain <pit@...>
Date: 2002-04-27T00:30:39+09:00
Subject: Re: expand_path and overlap

On 26 Apr 2002, at 23:08, nobu.nokada@softhome.net wrote:

> At Fri, 26 Apr 2002 22:42:03 +0900,
> Morris, Chris <chris.morris@snelling.com> wrote:
> > > I find this an interesting puzzle.  Question:  what would this
> > > return:
> > > 
> > >    collapse_path("b/c/f", "/a/b/c/d/e/b/c/g/h")
> > >    #^^^^^^^^^^^^ or whatever :-)
> > 
> > At the moment, I'm thinking it should be:
> > 
> >   /a/b/c/d/e/b/c/f
> > 
> > (which could probably be gathered from my other recent post :)
> 
> I'm not sure, is this like what you want?
> 
>   def collapse_path(path, base)
>     head, = path.split("/", 2)
>     base.rindex(%r"(\A|.*/)#{Regexp.quote(head)}(?:/|\z)")
>     ($1 or base) + path
>   end

Here are two other implementations (using only the basic regular 
expressions I can understand :-)

def collapse_path1( path, base )
  pattern = Regexp.quote( path.sub( /(.)\/.*/, '\1' ) )
  base.dup.sub!( /(.*)#{pattern}(\/|$).*/, '\1' + path ) || path
end

def collapse_path2( path, base )
  pattern = Regexp.quote( path.dup )
  while pattern
    return $1 + path if base =~ /(.*)#{pattern}(\/|$)/
    pattern.sub!( /(.*)\/.*/, '\1' )
  end
  return path
end

collapse_path1( "/b/c/f", "/a/b/c/d/e/b/x/g/h" ) # => /a/b/c/d/e/b/c/f
collapse_path2( "/b/c/f", "/a/b/c/d/e/b/x/g/h" ) # => /a/b/c/f

Don't know which one you want.

Regards,
Pit