In the following example the routes can determine if the URI is an alias, a file, a directory, or is the root path.

#!/usr/bin/ruby

# file: test.rb

require 'sinatra'


get '/' do
"home"
end

get '/:file*.*' do
"file"
end

get '/:alias' do
"alias"
end

get '/:directory/' do
"directory"
end


Tested (http://niko:4567)        observed

-----------------------          --------

              /README            alias

              /README/           directory

              /README/fun.txt    file

              /fun               alias

              /                  home

              /home.txt          file

              /home.txt/         file 

              /home/file.txt     file

              /home/f            Sinatra doesn't know this ditty

              /home/             directory

              /home?edit=1       alias

              /home/?edit=1      directory

              /home.xml?edit=1   file

Note: Alias in this context means a URI which will be redirected to another URI

Resources:
- Sinatra: README [sinatrarb.com]

Read more: http://feeds.dzone.com/~r/dzone/snippets/~3/bI_RwZBxOqk/11051