To specify the source field as metadata to be injected, perform the following steps: In the Target injection step key column, double-click the field for which you want to specify a source field. The Source field dialog box opens. Select a source field and click OK. (Optional) Select Use constant value to specify a constant value for the injected metadata through one of the following actions: Manually entering a value. Using an internal variable to set the value: ${Internal.Step.Unique.Count}, for example. Using a combination of manually specified values and parameter values: ${FILE_PREFIX}_${FILE_DATE}.txt, for example.