{ <field>: { $regex: /pattern/, $options: '<options>' } }
{ <field>: { $regex: 'pattern', $options: '<options>' } }
{ <field>: { $regex: /pattern/<options> } }
In MongoDB, you can also use regular expression objects (i.e.
/pattern/) to specify regular expressions:
{ <field>: /pattern/<options> }
For restrictions on particular syntax use, see
$regex vs. /pattern/ Syntax.
$options¶
The following <options> are available for use with regular
expression.
Case insensitivity to match upper and lower cases.
For an example, see Perform Case-Insensitive Regular Expression Match.
For patterns that include anchors (i.e. ^ for the start,
$ for the end), match at the beginning or end of each
line for strings with multiline values. Without this option,
these anchors match at beginning or end of the string. For an
example, see Multiline Match for Lines Starting with Specified Pattern.
If the pattern contains no anchors or if the string value has
no newline characters (e.g. \n), the m option has no
effect.
“Extended” capability to ignore all white space characters in
the $regex pattern unless escaped or included in a
character class.
Additionally, it ignores characters in-between and including
an un-escaped hash/pound (#) character and the next new
line, so that you may include comments in complicated
patterns. This only applies to data characters; white space
characters may never appear within special character
sequences in a pattern.
The x option does not affect the handling of the VT
character (i.e. code 11).
Requires $regex with $options syntax
Allows the dot character (i.e. .) to match all
characters including newline characters. For an example,
see Use the . Dot Character to Match New Line.
Requires $regex with $options syntax
$in Expressions¶
To include a regular expression in an $in query expression, you can
only use JavaScript regular expression objects (i.e. /pattern/
). For example:
{ name: { $in: [ /^acme/i, /^ack/ ] } }
You cannot use $regex operator expressions inside an
$in.
Implicit AND Conditions for the Field¶
To include a regular expression in a comma-separated list of query
conditions for the field, use the $regex operator. For example:
{ name: { $regex: /acme.*corp/i, $nin: [ 'acmeblahcorp' ] } }
{ name: { $regex: /acme.*corp/, $options: 'i', $nin: [ 'acmeblahcorp' ] } }
{ name: { $regex: 'acme.*corp', $options: 'i', $nin: [ 'acmeblahcorp' ] } }
x and s Options¶
To use either the x option or s options, you must use the
$regex operator expression with the $options
operator. For example, to specify the i and the s options, you
must use $options for both:
{ name: { $regex: /acme.*corp/, $options: "si" } }
{ name: { $regex: 'acme.*corp', $options: "si" } }
PCRE vs JavaScript¶
To use PCRE supported features in the regex pattern that are
unsupported in JavaScript, you must use the $regex operator
expression with the pattern as a string. For example, to use (?i)
in the pattern to turn case-insensitivity on for the remaining pattern
and (?-i) to turn case-sensitivity on for the remaining pattern, you
must use the $regex operator with the pattern as a string:
{ name: { $regex: '(?i)a(?-i)cme' } }
Index Use¶
For case sensitive regular expression queries, if an index exists for
the field, then MongoDB matches the regular expression against the
values in the index, which can be faster than a collection scan.
Further optimization can occur if the regular expression is a “prefix
expression”, which means that all potential matches start with the same
string. This allows MongoDB to construct a “range” from that prefix and
only match against those values from the index that fall within that
range.
A regular expression is a “prefix expression” if it starts with a caret
(^) or a left anchor (\A), followed by a string of simple
symbols. For example, the regex /^abc.*/ will be optimized by
matching only against the values from the index that start with abc.
Additionally, while /^a/, /^a.*/, and /^a.*$/ match
equivalent strings, they have different performance characteristics.
All of these expressions use an index if an appropriate index
exists; however, /^a.*/, and /^a.*$/ are slower. /^a/
can stop scanning after matching the prefix.
Case insensitive regular expression queries generally cannot use indexes
effectively. The $regex implementation is not collation-aware
and is unable to utilize case-insensitive indexes.
Examples¶
The following examples use a collection products with the following
documents:
{ "_id" : 100, "sku" : "abc123", "description" : "Single line description." }
{ "_id" : 101, "sku" : "abc789", "description" : "First line\nSecond line" }
{ "_id" : 102, "sku" : "xyz456", "description" : "Many spaces before     line" }
{ "_id" : 103, "sku" : "xyz789", "description" : "Multiple\nline description" }
Perform a LIKE Match¶
The following example matches all documents where the sku field is
like "%789":
db.products.find( { sku: { $regex: /789$/ } } )
The example is analogous to the following SQL LIKE statement:
SELECT * FROM products
WHERE sku like "%789";
Perform Case-Insensitive Regular Expression Match¶
The following example uses the i option perform a
case-insensitive match for documents with sku value that starts
with ABC.
db.products.find( { sku: { $regex: /^ABC/i } } )
The query matches the following documents:
{ "_id" : 100, "sku" : "abc123", "description" : "Single line description." }
{ "_id" : 101, "sku" : "abc789", "description" : "First line\nSecond line" }
Multiline Match for Lines Starting with Specified Pattern¶
The following example uses the m option to match lines starting
with the letter S for multiline strings:
db.products.find( { description: { $regex: /^S/, $options: 'm' } } )
The query matches the following documents:
{ "_id" : 100, "sku" : "abc123", "description" : "Single line description." }
{ "_id" : 101, "sku" : "abc789", "description" : "First line\nSecond line" }
Without the m option, the query would match just the following document:
{ "_id" : 100, "sku" : "abc123", "description" : "Single line description." }
If the $regex pattern does not contain an anchor, the pattern
matches against the string as a whole, as in the following example:
db.products.find( { description: { $regex: /S/ } } )
Then, the $regex would match both documents:
{ "_id" : 100, "sku" : "abc123", "description" : "Single line description." }
{ "_id" : 101, "sku" : "abc789", "description" : "First line\nSecond line" }
Use the . Dot Character to Match New Line¶
The following example uses the s option to allow the  dot
character (i.e. .) to match all characters including new line as well as the
i option to perform a case-insensitive match:
db.products.find( { description: { $regex: /m.*line/, $options: 'si' } } )
The query matches the following documents:
{ "_id" : 102, "sku" : "xyz456", "description" : "Many spaces before     line" }
{ "_id" : 103, "sku" : "xyz789", "description" : "Multiple\nline description" }
Without the s option, the query would have matched only the following document:
{ "_id" : 102, "sku" : "xyz456", "description" : "Many spaces before     line" }
Ignore White Spaces in Pattern¶
The following example uses the x option ignore white spaces and the
comments, denoted by the # and ending with the \n in the
matching pattern:
var pattern = "abc #category code\n123 #item number"
db.products.find( { sku: { $regex: pattern, $options: "x" } } )
The query matches the following document:
{ "_id" : 100, "sku" : "abc123", "description" : "Single line description." }