Writing a scripted lookup to enrich data

We covered CSV lookups fairly extensively in Chapter 7, Extending Search, then touched on them again in Chapter 10, Summary Indexes and CSV Files, and Chapter 11, Configuring Splunk. The capabilities built into Splunk are usually sufficient, but sometimes, it is necessary to use an external data source or dynamic logic to calculate values. Scripted lookups have the following advantages over commands and CSV lookups:

• Scripted lookups are only run once per unique lookup value, as opposed to a command, which would run the command for every event.
• The memory requirement of a CSV lookup increases with the size of the CSV file.
• Rapidly-changing values can be left in an external system and queried using the scripted lookup instead of being exported frequently. In the Using a lookup with wildcards section in Chapter 10, Summary Indexes and CSV Files, we essentially created a case statement through configuration. Let's implement that use case as a script, just...