How do I store a large number of regex and find the regex that has a match for a given string?

We generally use regex to match with strings. I want to do it the other way around. I have a large number of regex. Now, given a string, I should identify which regex had a match with the string. How do I do this?

I was considering storing all the regex in Elasticsearch and then query it using the string, but I am not able to find any documentation to see if it possible.

I could store all the regex in a DB, get the ones I want to check matches and then find matches, but is there a better way to do it?

It's possible to do this using the percolator field type.

You can basically index all your regexp queries and then test which of the queries would match your document.

Create the index with a percolator field type:

PUT regex
{
  "mappings": {
    "properties": {
      "message": {
        "type": "keyword"
      },
      "query": {
        "type": "percolator"
      }
    }
  }
}

Index two regular expressions, for instance:

PUT /regex/_doc/1
{
  "query": {
    "regexp": {
      "message": {
        "value": "big.*fox",
        "flags": "ALL",
        "case_insensitive": true
      }
    }
  }
}

PUT /regex/_doc/2
{
  "query": {
    "regexp": {
      "message": {
        "value": ".*fox",
        "flags": "ALL",
        "case_insensitive": true
      }
    }
  }
}

Then test which regular expression would match your input.

Percolating big brown fox would match both regular expressions above:

POST regex/_search
{
  "query": {
    "percolate": {
      "field": "query",
      "document": {
        "message": "big brown fox"
      }
    }
  }
}

Percolating big brown bear would match none of the above:

POST regex/_search
{
  "query": {
    "percolate": {
      "field": "query",
      "document": {
        "message": "big brown bear"
      }
    }
  }
}