title: custom fast cgi cache duration for each location
body: <p>i have this configure</p>
  <pre><code>location ~* \.php$ {
          try_files $uri /index.php =404;
          fastcgi_pass phpstream;
          fastcgi_index index.php;
          fastcgi_cache GCache;
          fastcgi_cache_valid 200 120m;
          fastcgi_cache_min_uses 1;
  }
  </code></pre>
  <p>i wanna make the duration dynamic for some locations instead of <code>120m</code> for all so i tried</p>
  <pre><code>location ~* \.php$ {
          try_files $uri /index.php =404;
          fastcgi_pass phpstream;
          fastcgi_index index.php;
  
          set $duration = 120m;
          if ($request_uri ~ ^/([0-9]+)/$) { 
              set $duration 30s;
          }
  
          fastcgi_cache GCache;
          fastcgi_cache_valid 200 $duration;
          fastcgi_cache_min_uses 1;
  }
  </code></pre>
  <p>but i get error</p>
  <pre><code>2022/08/21 22:11:12 [emerg] 1#1: invalid time value &quot;$duration&quot; in /etc/nginx/conf.d/data.conf
  nginx: [emerg] invalid time value &quot;$duration&quot; in /etc/nginx/conf.d/data.conf
  </code></pre>
  <p>i wanna make it 30s for dynamic content so it updates every 30s if the dynamic content updated but the rest is different</p>