[[query-dsl-regexp-query]]
=== Regexp Query

The `regexp` query allows you to use regular expression term queries.

*Note*: The performance of a `regexp` query heavily depends on the
regular expression chosen. Matching everything like `.*` is very slow as
well as using lookaround regular expressions. If possible, you should
try to use a long prefix before your regular expression starts. Wildcard
matchers like `.*?+` will mostly lower performance.

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

Boosting is also supported

[source,js]
--------------------------------------------------
{
    "regexp":{
        "name.first":{
            "value":"s.*y",
            "boost":1.2
        }
    }
}
--------------------------------------------------

You can also use special flags

[source,js]
--------------------------------------------------
{
    "regexp":{
        "name.first": "s.*y",
        "flags" : "INTERSECTION|COMPLEMENT|EMPTY"
    }
}
--------------------------------------------------

Possible flags are `ALL`, `ANYSTRING`, `AUTOMATON`, `COMPLEMENT`,
`EMPTY`, `INTERSECTION`, `INTERVAL`, or `NONE`. Please check the
http://lucene.apache.org/core/4_3_0/core/index.html?org%2Fapache%2Flucene%2Futil%2Fautomaton%2FRegExp.html[Lucene
documentation] for their meaning

For more information see the
http://lucene.apache.org/core/4_3_0/core/index.html?org%2Fapache%2Flucene%2Fsearch%2FRegexpQuery.html[Lucene
RegexpQuery documentation].
