[[query-dsl-regexp-filter]]
=== Regexp Filter

The `regexp` filter is similar to the
<<query-dsl-regexp-query,regexp>> query, except
that it is cacheable and can speedup performance in case you are reusing
this filter in your queries.

See <<regexp-syntax>> for details of the supported regular expression language.

[source,js]
--------------------------------------------------
{
    "filtered": {
        "query": {
            "match_all": {}
        },
        "filter": {
            "regexp":{
                "name.first" : "s.*y"
            }
        }
    }
}
--------------------------------------------------

You can also select the cache name and use the same regexp flags in the
filter as in the query.

*Note*: You have to enable caching explicitly in order to have the
`regexp` filter cached.

[source,js]
--------------------------------------------------
{
    "filtered": {
        "query": {
            "match_all": {}
        },
        "filter": {
            "regexp":{
                "name.first" : {
                    "value" : "s.*y",
                    "flags" : "INTERSECTION|COMPLEMENT|EMPTY"
                },
                "_name":"test",
                "_cache" : true,
                "_cache_key" : "key"
            }
        }
    }
}
--------------------------------------------------