Page Comparison

The syntax of an explicit logging statement is:

log <expr> 

where <expr> is any valid KRL expression that results in a string (or something that can be cast as a string such as a number).
The following example would place a string with the value of a variable named query in the log if the rule fired:

fired { log "query:"+query } 

The following would only log with an empty query:

fired { log "Empty query" if(query like "^$") }

The following rule is selected when an http:post() event is raised indicating a error status code. The error is logged and then processing is stopped. 

rule r3 is active {

...

  select when http post label re#ex# status_code re#([45]\d\d)#

...

 setting (status)

...

  noop();
  fired {
    log <<Error: #{status}: #{event:attr("status_line")}>>

...

    last;

...

  }
}

...

Another approach would use explicit error handling.