# Specify the source field

To specify the source field as metadata to be injected, perform the following steps:

1. 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.

   ![PDI ETL Metadata Source field dialog box](/files/ZghP2VZwhmOux041eSIx)
2. Select a source field and click **OK**.
3. (Optional) Type a word in the **Filter** field and click the **Search** icon to search for fields with that name. Click the **Regex** icon to search using Java regular expressions.
4. (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.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.pentaho.com/pdia-data-integration/10.2-data-integration/pdi-transformation-steps-reference-overview/etl-metadata-injection/options-etl-metadata-injection/inject-metadata-tab/specify-the-source-field.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.