AVAILABLE ON {{}http://grokconstructor.appspot.com/
Grok is a collection of named regular expressions that can be used - for instance with logstash http://logstash.net/ - to parse logfiles. GrokDiscovery http://grokdebug.herokuapp.com/ can somewhat help you by suggesting regular expressions. GrokConstructor goes beyond that by finding many possible regular expressions that match a whole set of logfile lines by using groks patterns and fixed strings. This can be done automatically (which is of limited use only for small stuff), or in a incremental process.
The best way is probably to use it on http://grokconstructor.appspot.com/ - there is also a good description, and you can use it on some examples or for your own log lines you want to match.
To run locally, build with mvn clean install and start with mvn appengine:devserver . It runs on http://localhost:9090/ .
If you want to run it on a system without internet connection or that has an application server, anyway, you can also deploy the created target/GrokConstructor-*-SNAPSHOT.war e.g. on a Tomcat.
java -jar GrokConstructor-0.1.0-SNAPSHOT-standalone.jar
runs an embedded Tomcat that makes it available at http://localhost:8080/ . Please be aware that this creates a directory .extract in the current directory that contains the unpacked webapp. You can print additional arguments (such as ports, unpack location) with
java -jar GrokConstructor-0.1.0-SNAPSHOT-standalone.jar -h