GET stackoverflow/_search
{
  "_source": false,
  "aggs": {
    "groups": {
      "terms": {
        "field": "text.keyword",
        "include": "LOC.*"
      }
    }
  }
}

GET stackoverflow/_search
{
  "_source": false,
  "aggs": {
    "groups": {
      "terms": {
        "field": "text.keyword",
        "include": "L.*"
      }
    }
  }
}

"buckets" : [
    {
      "key" : "LOCK",
      "doc_count" : 1
    },
    {
      "key" : "LOL",
      "doc_count" : 1
    }
]