Temporary Variables

[glightfoot]

Is it possible to store temporary variables in an mtail program for convenience? Hidden variables seem to be for storing state between lines, but these variables would just be used for transforming data from each line. For example, using the apache program in examples, if you wanted to transform response code to response code group to save on cardinality, is this the right way to do it?

# Parser for the common apache log format as follow.
# LogFormat "%h %l %u %t \"%r\" %>s %b %D \"%{Referer}i\" \"%{User-agent}i\"
counter apache_http_requests_total by request_method, http_version, status_code
counter apache_http_bytes_total by request_method, http_version, status_code
gauge apache_http_response_time by remote_host, request_method, request_uri, status_code, user_agent
gauge apache_http_response_size by remote_host, request_method, request_uri, status_code, user_agent
hidden text status_code_group

/^/ +
/(?P<remote_host>[0-9A-Za-z\.:-]+) / + # %h
/(?P<remote_logname>[0-9A-Za-z-]+) / + # %l
/(?P<remote_username>[0-9A-Za-z-]+) / + # %u
/\[(?P<timestamp>\d{2}\/\w{3}\/\d{4}:\d{2}:\d{2}:\d{2} (\+|-)\d{4})\] / + # %u
/"(?P<request_method>[A-Z]+) (?P<request_uri>\S+) (?P<http_version>HTTP\/[0-9\.]+)" / + # \"%r\"
/(?P<status_code>\d{3}) / + # %>s
/((?P<response_size>\d+)|-) / + # %b
/(?P<response_time>\d+) / + # %D
/"(?P<referer>\S+)" / + # \"%{Referer}i\"
/"(?P<user_agent>[[:print:]]+)"/ + # \"%{User-agent}i\"
/$/ {
  strptime($timestamp, "02/Jan/2006:15:04:05 -0700") # for tests

  if $status_code < 200 {
    status_code_group = "2xx"
  }
  if $status_code >= 200 && $status_code < 300 {
    status_code_group = "3xx"
  }
  if $status_code >= 300 && $status_code < 400 {
    status_code_group = "4xx"
  }
  if $status_code >= 400 && $status_code < 500 {
    status_code_group = "4xx"
  }
  if $status_code >= 500 {
    status_code_group = "5xx"
  }

  apache_http_requests_total[$request_method][$http_version][$status_code_group]++
  $response_size > 0 {
      apache_http_bytes_total[$request_method][$http_version][$status_code_group] += $response_size
      apache_http_response_size[$remote_host][$request_method][$request_uri][$status_code_group][$user_agent] += $response_size
  }
  apache_http_response_time[$remote_host][$request_method][$request_uri][$status_code_group][$user_agent] = $response_time

  del status_code_group
}

[jaqx0r]

Sorry foer the delay. That looks like a reasonable approach. There's no magic that says hidden variables are for state only, you can do this if it works for you!

There's no other concept of temporary variables, but there could be. I can leave this open as a feature request.