Defines the actual grok pattern used to evaluate data. You can enter a
predefined grok pattern, such as %{COMMONAPACHELOG}. Or, to define a custom
grok pattern, you can use the patterns listed in this appendix or the
patterns that you defined in Grok Pattern Description.

For example, after defining the patterns above in the Grok Pattern
Description field, you can use the patterns to configure Grok Pattern as
follows:

%{MYCUSTOMPATTERN} %{DURATIONLOG}

The following image shows the configuration example in the UI:

General Grok Patterns

You can use the following general grok patterns to define the structure of log data: