# Logstash: How to Add File Name as a Field?

To add the file name as a field in Logstash, you can use the `path` metadata provided by the `file` input plugin. Here’s a basic configuration:

1. **Use the `file` input plugin**: Capture the `path` value (the file’s full path).
2. **Extract the file name**: Use a filter to isolate the file name and add it as a field.

### Example Configuration

```
input {
  file {
    path => "/path/to/your/files/*.log"  # Adjust path as needed
    start_position => "beginning"
    sincedb_path => "/dev/null"  # For testing purposes; adjust as needed
  }
}

filter {
  grok {
    match => { "path" => "/path/to/your/files/%{GREEDYDATA:filename}.log" }
  }
}

output {
  stdout {
    codec => rubydebug  # Displays events on the console for debugging
  }
}
```

### Explanation

- **`%{GREEDYDATA:filename}`**: Extracts the filename from the `path`. Adjust the path pattern if necessary.
- **`filename`**: Stores the extracted file name in a new field named `filename` in each log event.

This setup will include the file name as a separate field in your Logstash output, making it easier to filter and analyze logs by file source.