If the destination field for the eval command already exists, what happens to it?

When using the eval command in Splunk, if the destination field specified already exists, the command will overwrite the contents of that field with the new value calculated or defined by the eval expression. This means that the previous value in the field will be replaced entirely, and the field will reflect the new result only.

In many data manipulation situations, overwriting existing fields allows for cleaner data management and ensures that the most relevant or latest information is displayed without retaining outdated values. This is particularly useful when performing calculations or transformations where the context of the original field is no longer necessary or relevant once the new computation is applied.

The other outcomes, such as ignoring the field, appending an integer, or keeping it unchanged, would not happen; the existing field's data is indeed replaced with the output from the eval command.