Best way to get the $request_uri without the starting slash

[Matthew Ward]

I want to pass the $request_uri to memcached as the key but without the starting slash, as our memcached key names are a prefixed integer which can be referenced from the URI, as follows:

http://example.com/1000 -> prefix:1000

In nginx, the only (or all) variables that refer to the URI also contain the starting slash. So if I were to use prefix:$request_uri as above I would get prefix:/1000 as the key.

At the moment I'm solving this by using a regex conditional to set a key name (this is paraphrased):

if ($request_uri ~* ^/(.*)$) {
  set $request_key $1;
}

set $memcached_key prefix:$request_key;

So now I have the correct key name for memcached. Are there any better ways of doing this? Would this have a serious impact on performance, performing this conditional every time? Is it possible do this using set without the conditional part?

Thanks for any help,
Matt.