Debugging new logstash grok filters before full use

As far as debugging a grok filter goes, you can use this link (http://grokdebug.herokuapp.com/) It has a very comprehensive pattern detector which is a good start.

As far your file output, you need "" around your path. Here is the example i use in production. Here is the documentation on file output http://logstash.net/docs/1.4.2/outputs/file#path

output {
    stdout {
        codec => rubydebug
    }
    file {
        codec => "plain"
        path => "./logs/logs-%{+YYYY-MM-dd}.txt"
    }
}

The Grokconstructor is a similar Grok debugger to Grokdebug which @user3195649 mentioned. I like it's random examples.