After some digging, I am able to gather the following
1. Every template is passed an object scope#Middleware::Server and local#Hash
2. request is available (as part of being Rack middleware). I ended up using request.path . Here's a request object instance from my app
#<Sinatra::Request:0x00000103de5630
@env=
{"rack.version"=>[1, 1],
"rack.input"=>#<StringIO:0x00000103de6030>,
"rack.errors"=>#<StringIO:0x00000103de60d0>,
"rack.multithread"=>true,
"rack.multiprocess"=>true,
"rack.run_once"=>false,
"REQUEST_METHOD"=>"GET",
"SERVER_NAME"=>"
example.org",
"SERVER_PORT"=>"80",
"QUERY_STRING"=>"",
"PATH_INFO"=>"/tutorials/measles/mmr06.html",
"rack.url_scheme"=>"http",
"HTTPS"=>"off",
"SCRIPT_NAME"=>"",
"CONTENT_LENGTH"=>"0",
"rack.test"=>true,
"REMOTE_ADDR"=>"127.0.0.1",
"HTTP_HOST"=>"
example.org",
"HTTP_COOKIE"=>"",
"rack.request.query_string"=>"",
"rack.request.query_hash"=>{}},
@params={},
@route="/tutorials/measles/mmr06.html">
-Amitava