conditional log for tengine.

example:

http {

    log_env $tmd {
        if ($uri != '/us');
        if ($status != 200);
    }   

    log_env $tmd1 {
        if ($uri != '/usr');
        sample .25;
    }   

    log_env $tmd2 {
        sample 1;
    }   

    map $r $d {
        1 0;
    }   

    server {
        listen 3130 default;

        set $r 1;

        log_condition {
            if ($status != 200);
            if ($uri != '/us');
            sample 0.5;
        }   


        location /us {
            empty_gif;

            access_log logs/access6.log combined env=$tmd1;
            access_log logs/access7.log combined;
        }   

        location /usr {

            empty_gif;

            access_log logs/aaaa;
            access_log logs/access1.log combined ratio=.25;
            access_log logs/access2.log combined env=$tmd;
            access_log logs/access3.log combined env=$tmd1 ratio=.1;
            access_log logs/access4.log combined env=$tmd2 ratio=.2;
            access_log logs/access5.log combined ratio=.5 env=$tmd2;
            access_log logs/access8.log combined ratio=.5 env=$r;
            access_log logs/access9.log combined ratio=.5 env=$d;
            #access_log logs/access9.log combined ratio=.5 env=$k;              error: $k is not defined
            #access_log logs/access2.log combined env=$tmd2 env=$tmd1;          error: env is duplicate
        }
}