New posts in Logstash Grok

How do I refer to a regex group inside a custom grok pattern?

Is there any existing grok{} pattern for date format YYYY/MM/DD HH:mm:ss?

Debugging new logstash grok filters before full use

How do I match a newline in grok/logstash?

List of SYNTAX for logstash's grok

Grok pattern for data separated by pipe