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
    }

}