Help Searching the data from my index

[snowfall_2010 (Snowfall James)]

my index save data structure is the pic below:

index info:

"1":{
    "aliases":{},
    "mappings":{
        "properties":{
            "DeviceId":{
                "type":"text",
                "fields":{
                    "keyword":{
                        "type":"keyword",
                        "ignore_above":256
                    }
                }
            },
            "Duration":{
                "type":"text",
                "fields":{
                    "keyword":{
                        "type":"keyword",
                        "ignore_above":256
                    }
                }
            },
            "FileName":{
                "type":"text",
                "fields":{
                    "keyword":{
                        "type":"keyword",
                        "ignore_above":256
                    }
                },
                "fielddata":true
            },
            "Hls":{
                "type":"text",
                "fields":{
                    "keyword":{
                        "type":"keyword",
                        "ignore_above":256
                    }
                }
            },
            "StartAt":{
                "type":"text",
                "fields":{
                    "keyword":{
                        "type":"keyword",
                        "ignore_above":256
                    }
                }
            }
        }
    },
    "settings":{
        "index":{
            "creation_date":"1589015659889",
            "number_of_shards":"1",
            "number_of_replicas":"1",
            "uuid":"JRmRGN7GSpOU4NfrHyTJ_g",
            "version":{
                "created":"7060299"
            },
            "provided_name":"1"
        }
    }
}

}

I have a requirement to search the filename field. FileName 's structure is IndexName/YYYYMMDD/hhmmss.m3u8.
I need to find out which day of the month there is a file name record.

Date infomation is only stored in FileName.

Any Sugguestion?

[warkolm (Mark Walkom)]

Your best option is to split that out into it's own field.
You might be able to do that with a script, but that's outside my knowledge sorry.

[snowfall_2010 (Snowfall James)]

thx for reply

[Vinayak_Sapre]

Snowfall,
Are you trying to search docs for a specific date or extract unique dates from docs? For later you can use script as suggested by Mark

{
  "size": 0,
  "aggs": {
    "dates": {
      "terms": {
        "field": "FileName.keyword",
        "script": {
          "source": "int s1 = _value.indexOf('/'); int s2 = _value.indexOf('/', s1+1); _value.substring(s1+1,s2)",
          "lang": "painless"
        }
      }
    }
  }
}