Which command is commonly used for field extraction that utilizes regular expressions?

The command that is commonly used for field extraction utilizing regular expressions is "rex." This command allows users to extract fields from their event data by applying a specified regular expression directly to the event's content. When you use the rex command, you can define a pattern that matches the structure of the data and capture specific parts of the information you want as fields.

Regular expressions provide a flexible way to match complex string patterns, making the rex command particularly powerful for dealing with unstructured or semi-structured log data. Through this command, you can specify which parts of the log entry should become new fields in your results, effectively allowing for tailored and precise data extraction.

The other choices do not serve the same purpose. The spath command, for instance, is used specifically for extracting fields from structured data formats like JSON or XML, but it does not utilize regular expressions. The eval command is focused on evaluating expressions to create or modify fields but does not directly handle field extraction using regex. Lastly, sort is used to arrange the results in a specified order and does not relate to field extraction. Thus, using the rex command is the appropriate method for scenarios requiring regex-based field extraction in Splunk.