$conn_requests
the sequence number of current request in the keepalive connection.
$dollar
The sign of dollar.
$request_time_msec
The request processing time, which is in milliseconds, only used in log_format.
$request_time_usec
The request processing time, which is in microseconds, only used in log_format.
$unix_time
The current timestamp, it's the current second since the epoch time of Unix.
$year
Current year, e.g. 2011.
$year2
Current year, e.g. 11.
$month
Current month, e.g. 03, 12.
$day
Current day, e.g. 03, 22.
$hour
Current hour (24), e.g. 02, 21.
$hour12
Current hour (12), e.g. 02, 09.
$minute
Current minute, e.g. 35.
$second
Current second, e.g. 12.
$sent_cookie_XXX
The cookie value of XXX in the Set-Cookie headers.
$host_comment
Host and the timestamp, e.g. “<!-- localhost Thu, 29 Dec 2011 10:10:56 GMT -->”.
$ssl_handshake_time
used for monitoring SSL handshake time.