How to write only logs with 200 status

nginx 1.7.0+ allows using an if condition in access_log directive itself.

access_log path [format [buffer=size [flush=time]] [if=condition]];The if parameter (1.7.0) enables conditional logging.A request will not be logged if the condition evaluates to “0” or an empty string

Combined with map directive its possible to send log events to different logs based on various conditions.

http {    map $status $normal {        ~^2  1;        default 0;    }    map $status $abnormal {        ~^2  0;        default 1;    }    map $remote_addr $islocal {        ~^127  1;        default 0;    }    server {        access_log logs/access.log combined if=$normal;        access_log logs/access_abnormal.log combined if=$abnormal;        access_log logs/access_local.log combined if=$islocal;    }  }

http://nginx.org/en/docs/http/ngx_http_log_module.html
http://nginx.org/en/docs/http/ngx_http_map_module.html

you can do it by using ngx.log and log_by_lua directives.

location /conditional_log{        log_by_lua 'if ngx.status == 200 then ngx.log(ngx.ERR, "It is 200") end';        content_by_lua 'ngx.say("I am ok") ngx.exit(200)';    }

In the above code, we use log_by_lua which is called while running in log phase. In that if ngx.status == 200, we use ngx.log to trigger the logging using ngx.log.

This will write to error_log. Not sure how to write it to access_log.

For reference

http://wiki.nginx.org/HttpLuaModule#ngx.log

http://wiki.nginx.org/HttpLuaModule#log_by_lua

In every question is a part of answer. You were very close:

if ($status != "200") {    access_log off;}

Check info for version availability here.http://nginx.org/en/docs/http/ngx_http_core_module.html#variables

Also, almost all access log format vars are available in "modern" versions:http://nginx.org/en/docs/http/ngx_http_log_module.html