Regexp Query
editRegexp Query
editThe regexp
query allows you to use regular expression term queries.
See Regular expression syntax for details of the supported regular expression language.
The "term queries" in that first sentence means that Elasticsearch will apply
the regexp to the terms produced by the tokenizer for that field, and not
to the original text of the field.
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.
GET /_search { "query": { "regexp":{ "name.first": "s.*y" } } }
Boosting is also supported
GET /_search { "query": { "regexp":{ "name.first":{ "value":"s.*y", "boost":1.2 } } } }
You can also use special flags
GET /_search { "query": { "regexp":{ "name.first": { "value": "s.*y", "flags" : "INTERSECTION|COMPLEMENT|EMPTY" } } } }
Possible flags are ALL
(default), ANYSTRING
, COMPLEMENT
,
EMPTY
, INTERSECTION
, INTERVAL
, or NONE
. Please check the
Lucene
documentation for their meaning
Regular expressions are dangerous because it’s easy to accidentally
create an innocuous looking one that requires an exponential number of
internal determinized automaton states (and corresponding RAM and CPU)
for Lucene to execute. Lucene prevents these using the
max_determinized_states
setting (defaults to 10000). You can raise
this limit to allow more complex regular expressions to execute.
GET /_search { "query": { "regexp":{ "name.first": { "value": "s.*y", "flags" : "INTERSECTION|COMPLEMENT|EMPTY", "max_determinized_states": 20000 } } } }
By default the maximum length of regex string allowed in a Regexp Query
is limited to 1000. You can update the index.max_regex_length
index setting
to bypass this limit.
Regular expression syntax
editRegular expression queries are supported by the regexp
and the query_string
queries. The Lucene regular expression engine
is not Perl-compatible but supports a smaller range of operators.
We will not attempt to explain regular expressions, but just explain the supported operators.
Standard operators
edit- Anchoring
-
Most regular expression engines allow you to match any part of a string. If you want the regexp pattern to start at the beginning of the string or finish at the end of the string, then you have to anchor it specifically, using
^
to indicate the beginning or$
to indicate the end.Lucene’s patterns are always anchored. The pattern provided must match the entire string. For string
"abcde"
:ab.* # match abcd # no match
- Allowed characters
-
Any Unicode characters may be used in the pattern, but certain characters are reserved and must be escaped. The standard reserved characters are:
. ? + * | { } [ ] ( ) " \
If you enable optional features (see below) then these characters may also be reserved:
# @ & < > ~
Any reserved character can be escaped with a backslash
"\*"
including a literal backslash character:"\\"
Additionally, any characters (except double quotes) are interpreted literally when surrounded by double quotes:
john"@smith.com"
- Match any character
-
The period
"."
can be used to represent any character. For string"abcde"
:ab... # match a.c.e # match
- One-or-more
-
The plus sign
"+"
can be used to repeat the preceding shortest pattern once or more times. For string"aaabbb"
:a+b+ # match aa+bb+ # match a+.+ # match aa+bbb+ # match
- Zero-or-more
-
The asterisk
"*"
can be used to match the preceding shortest pattern zero-or-more times. For string"aaabbb
":a*b* # match a*b*c* # match .*bbb.* # match aaa*bbb* # match
- Zero-or-one
-
The question mark
"?"
makes the preceding shortest pattern optional. It matches zero or one times. For string"aaabbb"
:aaa?bbb? # match aaaa?bbbb? # match .....?.? # match aa?bb? # no match
- Min-to-max
-
Curly brackets
"{}"
can be used to specify a minimum and (optionally) a maximum number of times the preceding shortest pattern can repeat. The allowed forms are:{5} # repeat exactly 5 times {2,5} # repeat at least twice and at most 5 times {2,} # repeat at least twice
For string
"aaabbb"
:a{3}b{3} # match a{2,4}b{2,4} # match a{2,}b{2,} # match .{3}.{3} # match a{4}b{4} # no match a{4,6}b{4,6} # no match a{4,}b{4,} # no match
- Grouping
-
Parentheses
"()"
can be used to form sub-patterns. The quantity operators listed above operate on the shortest previous pattern, which can be a group. For string"ababab"
:(ab)+ # match ab(ab)+ # match (..)+ # match (...)+ # no match (ab)* # match abab(ab)? # match ab(ab)? # no match (ab){3} # match (ab){1,2} # no match
- Alternation
-
The pipe symbol
"|"
acts as an OR operator. The match will succeed if the pattern on either the left-hand side OR the right-hand side matches. The alternation applies to the longest pattern, not the shortest. For string"aabb"
:aabb|bbaa # match aacc|bb # no match aa(cc|bb) # match a+|b+ # no match a+b+|b+a+ # match a+(b|c)+ # match
- Character classes
-
Ranges of potential characters may be represented as character classes by enclosing them in square brackets
"[]"
. A leading^
negates the character class. The allowed forms are:[abc] # 'a' or 'b' or 'c' [a-c] # 'a' or 'b' or 'c' [-abc] # '-' or 'a' or 'b' or 'c' [abc\-] # '-' or 'a' or 'b' or 'c' [^abc] # any character except 'a' or 'b' or 'c' [^a-c] # any character except 'a' or 'b' or 'c' [^-abc] # any character except '-' or 'a' or 'b' or 'c' [^abc\-] # any character except '-' or 'a' or 'b' or 'c'
Note that the dash
"-"
indicates a range of characters, unless it is the first character or if it is escaped with a backslash.For string
"abcd"
:ab[cd]+ # match [a-d]+ # match [^a-d]+ # no match
Optional operators
editThese operators are available by default as the flags
parameter defaults to ALL
.
Different flag combinations (concatenated with "|"
) can be used to enable/disable
specific operators:
{ "regexp": { "username": { "value": "john~athon<1-5>", "flags": "COMPLEMENT|INTERVAL" } } }
- Complement
-
The complement is probably the most useful option. The shortest pattern that follows a tilde
"~"
is negated. For instance, `"ab~cd" means:-
Starts with
a
-
Followed by
b
-
Followed by a string of any length that it anything but
c
-
Ends with
d
For the string
"abcdef"
:ab~df # match ab~cf # match ab~cdef # no match a~(cb)def # match a~(bc)def # no match
Enabled with the
COMPLEMENT
orALL
flags. -
Starts with
- Interval
-
The interval option enables the use of numeric ranges, enclosed by angle brackets
"<>"
. For string:"foo80"
:foo<1-100> # match foo<01-100> # match foo<001-100> # no match
Enabled with the
INTERVAL
orALL
flags. - Intersection
-
The ampersand
"&"
joins two patterns in a way that both of them have to match. For string"aaabbb"
:aaa.+&.+bbb # match aaa&bbb # no match
Using this feature usually means that you should rewrite your regular expression.
Enabled with the
INTERSECTION
orALL
flags. - Any string
-
The at sign
"@"
matches any string in its entirety. This could be combined with the intersection and complement above to express “everything except”. For instance:@&~(foo.+) # anything except string beginning with "foo"
Enabled with the
ANYSTRING
orALL
flags.