How to replace multiple new lines with one in Ingest Pipeline gsub

Elastic Stack Elasticsearch
4

Now it is just a regex exercise I am not a regex expert... but I did a quick google search found this

POST _ingest/pipeline/_simulate
{
  "pipeline": {
    "processors": [
      {
        "gsub": {
          "field": "message",
          "pattern": "\\\n+",
          "replacement": "\\\n",
          "ignore_missing": false,
          "description": "Replace multiple newlines",
          "on_failure": [
            {
              "append": {
                "description": "Record error information",
                "field": "_ingestion_errors",
                "value": "Processor 'gsub' with tag 'remove_page_numbers' in pipeline '{{ _ingest.on_failure_pipeline }}' failed with message '{{ _ingest.on_failure_message }}'"
              }
            }
          ]
        }
      }
    ]
  },
  "docs": [
    {
      "_source": {
        "message": """String with 
1 newline
Then 2 newlines

Then 3 Newlines



The End """
      }
    }
  ]
}

# Result
{
  "docs": [
    {
      "doc": {
        "_index": "_index",
        "_version": "-3",
        "_id": "_id",
        "_source": {
          "message": """String with 
1 newline
Then 2 newlines
Then 3 Newlines
The End """
        },
        "_ingest": {
          "timestamp": "2023-12-29T16:58:37.484845559Z"
        }
      }
    }
  ]
}