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$regexMatch

Definition

Tests whether a Java regular expression matches text.

Expression operator · Text · Studio Visual: available. Studio validates the complete expression separately.

Syntax

{
  "$regexMatch": {
    "input": <input>,
    "regex": <regex>,
    "options": <options>
  }
}

Replace angle-bracket placeholders with expressions or values.

Optional parameters may be omitted.

Parameters

Parameter Required Description
input Yes Expression supplying the value to process. A field reference such as "$price" reads from the current document.
regex Yes Regular-expression pattern to search for.
options No Regex option string. See Supported values below.

Supported values

options accepts any combination of i (case-insensitive), m (multiline anchors), s (dot matches newlines), and x (ignore pattern whitespace/comments). Omit it or use "" for no flags. Patterns use Java regular-expression behavior.

Behavior

The following observations use the example expression below. Each row substitutes one argument while retaining the other example arguments. A missing field differs from an explicit null; the result shown is what Core actually returned.

For the input argument:

Input case Supplied value Result
null null false
missing Field absent false
decimal 2.5 Error — $regexMatch input must be a string
numeric string "12" false
text "hello" false
boolean true Error — $regexMatch input must be a string
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $regexMatch input must be a string
empty array [] Error — $regexMatch input must be a string
numeric array [1,2,3] Error — $regexMatch input must be a string
object {"x":1} Error — $regexMatch input must be a string

Argument handling

Invocation Result
{"$regexMatch":[]} Error — $regexMatch requires input, regex and optional options
{"$regexMatch":{"unexpected":1}} Error — $regexMatch requires input, regex and optional options

Examples

Expression: 

{
  "$regexMatch": {
    "input": "abc",
    "regex": "ab"
  }
}

Input document: 

{}

Observed SrotaX result: true.

Detailed input cases

Expand the complete argument-by-argument test matrix

Each table changes only the indicated argument from the example above. Other arguments retain their baseline values. Values normally come from the input field probe; literal configuration arguments are replaced directly. “Missing” means the field is absent, not explicitly null. Numeric strings are strings, not numbers.

Argument: input

Input case Supplied value SrotaX result
null null false
missing Field absent false
zero 0 Error — $regexMatch input must be a string
negative -2 Error — $regexMatch input must be a string
decimal 2.5 Error — $regexMatch input must be a string
numeric string "12" false
text "hello" false
empty string "" false
boolean true Error — $regexMatch input must be a string
false false Error — $regexMatch input must be a string
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $regexMatch input must be a string
decimal128 {"$numberDecimal":"1.25"} Error — $regexMatch input must be a string
empty array [] Error — $regexMatch input must be a string
numeric array [1,2,3] Error — $regexMatch input must be a string
mixed array [1,null,"x",3] Error — $regexMatch input must be a string
nested array [[1,2],[3]] Error — $regexMatch input must be a string
empty object {} Error — $regexMatch input must be a string
object {"x":1} Error — $regexMatch input must be a string
ISO date string "2026-01-15T15:00:00Z" false
omitted named argument Argument removed Error — $regexMatch requires input, regex and optional options

Argument: regex

Input case Supplied value SrotaX result
null null false
missing Field absent false
zero 0 Error — $regexMatch regex must be a string or BSON regex
negative -2 Error — $regexMatch regex must be a string or BSON regex
decimal 2.5 Error — $regexMatch regex must be a string or BSON regex
numeric string "12" false
text "hello" false
empty string "" true
boolean true Error — $regexMatch regex must be a string or BSON regex
false false Error — $regexMatch regex must be a string or BSON regex
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $regexMatch regex must be a string or BSON regex
decimal128 {"$numberDecimal":"1.25"} Error — $regexMatch regex must be a string or BSON regex
empty array [] Error — $regexMatch regex must be a string or BSON regex
numeric array [1,2,3] Error — $regexMatch regex must be a string or BSON regex
mixed array [1,null,"x",3] Error — $regexMatch regex must be a string or BSON regex
nested array [[1,2],[3]] Error — $regexMatch regex must be a string or BSON regex
empty object {} Error — $regexMatch regex must be a string or BSON regex
object {"x":1} Error — $regexMatch regex must be a string or BSON regex
ISO date string "2026-01-15T15:00:00Z" false
omitted named argument Argument removed Error — $regexMatch requires input, regex and optional options

Argument: options

Input case Supplied value SrotaX result
null null true
missing Field absent true
zero 0 Error — $regexMatch options must be a string
negative -2 Error — $regexMatch options must be a string
decimal 2.5 Error — $regexMatch options must be a string
numeric string "12" Error — Unsupported regex option: 1
text "hello" Error — Unsupported regex option: h
empty string "" true
boolean true Error — $regexMatch options must be a string
false false Error — $regexMatch options must be a string
typed date {"$date":"2026-01-15T15:00:00Z"} Error — $regexMatch options must be a string
decimal128 {"$numberDecimal":"1.25"} Error — $regexMatch options must be a string
empty array [] Error — $regexMatch options must be a string
numeric array [1,2,3] Error — $regexMatch options must be a string
mixed array [1,null,"x",3] Error — $regexMatch options must be a string
nested array [[1,2],[3]] Error — $regexMatch options must be a string
empty object {} Error — $regexMatch options must be a string
object {"x":1} Error — $regexMatch options must be a string
ISO date string "2026-01-15T15:00:00Z" Error — Unsupported regex option: 2
omitted named argument Argument removed true

Additional boundary examples

Show 1 tested examples

Expression: 

{
  "$regexMatch": {
    "input": "a",
    "regex": "["
  }
}

Input: 

{}

SrotaX: Error — Unclosed character class near index 0 [ ^.

Verification

This page records 64 executed cases. It covers individual argument substitutions, not every cross-product of arguments, locale, daylight-saving transitions, numeric overflow, collation or resource limits. No untested behavior is guaranteed.

Download exact expressions, inputs and SrotaX results. Errors are observed messages, not stable public error codes. The reference generator reads the checked-in execution report; do not edit generated observations by hand.

MongoDB differences

Compared with MongoDB 9.0.4: 17 exact BSON matches, 47 both rejected, 0 value/type/acceptance differences, 0 object-field-order differences.

“Exact” includes numeric BSON types and object key order. A value of 3 as int32 differs from 3.0 as double. Object-field-order differences are reported separately; object key ordering is not enforced by the engine regression baseline. Both rejected does not mean the error codes or messages match. This is finite-case evidence, not full compatibility certification.

No differences were observed in the compared cases.

Download full comparison evidence.