Variable substitution issue

Hi (sorry for my bad english),

I just installed nginx for evaluation purpose on Gentoo GNU/Linux

#nginx -V
nginx version: nginx/0.7.6
configure arguments: --prefix=/usr --conf-path=/etc/nginx/nginx.conf
–http-log-path=/var/log/nginx/access_log
–error-log-path=/var/log/nginx/error_log --pid-path=/var/run/nginx.pid
–http-client-body-temp-path=/var/tmp/nginx/client
–http-proxy-temp-path=/var/tmp/nginx/proxy
–http-fastcgi-temp-path=/var/tmp/nginx/fastcgi --with-md5-asm
–with-md5=/usr/include --with-sha1-asm --with-sha1=/usr/include
–with-http_realip_module --with-http_flv_module --with-http_ssl_module

My typical configuration file (included into main config) for a vhost
is as follow:

server {
listen wiki.MySite.tld:80 ;
server_name wiki.MySite.tld ;

 set         $localpath                 /home/www/MySite.tld/wiki ;
 set         $localroot                 $localpath/htdocs ;

 access_log  $localpath/access.log main ;

 rewrite     ^/_media/(.*)              /lib/exe/fetch.php?media=$1

last;
rewrite ^/detail/(.) /lib/exe/detail.php?media=$1
last;
rewrite ^/_export/([^/]+)/(.
) /doku.php?do=export
$1&id=$2
last;

 location / {
     index index.php index.html ;
     root  $localroot ;
     if (!-f $request_filename) {
         rewrite ^/(.*)?(.*)            /doku.php?id=$1&$2 last;
         rewrite ^/$                    /doku.php last;
     }
 }

 location ~ \.php$ {
     include         /etc/nginx/php-fastcgi.conf ;
     fastcgi_index   index.php ;
     fastcgi_param   SCRIPT_FILENAME $localroot$fastcgi_script_name 

;
}
}

I encounter issue with access_log path (and error_log too but nginx
complains) wich seems not correctly computed. The result should be
“/home/www/MySite.tld/wiki/access.log”. Nnginx prepend “/usr/” before
$localpath. Strace is my spy:

open("/usr//home/www/MySite.tld/wiki/access.log",
O_RDWR|O_CREAT|O_APPEND|O_LARGEFILE, 0644) = -1 ENOENT (No such file or
directory)

Is my usage of “set” directive wrong ? Otherwise it seems to work
correctly with others ones.

Thx for your help.

Stephane.