What is the function of the 'fields' command in Splunk?

The 'fields' command in Splunk is primarily used to specify which fields should be included or excluded from search results. By using the 'fields' command, users can streamline their search output, allowing them to focus on the most relevant data and improve the readability of results. This is particularly useful when dealing with large datasets or when specific information is required for analysis.

For instance, if a search returns numerous fields but only a few are needed for the analysis, using the 'fields' command can help in refining the output by keeping only those necessary fields, thus enhancing performance and reducing clutter.

In contrast, defining the format of incoming data pertains to data ingestion configurations, which do not involve the 'fields' command. Filtering events based on specified conditions is typically done using other commands like 'where' or 'search', which are designed for event selection based on criteria rather than field inclusion/exclusion. Optimizing data retrieval based on usage patterns relates more to indexing and data model designs rather than the specific functionality of the 'fields' command.