---
type: "fhirpath-function"
title: "FHIRPath Function: matches"
function: "matches"
category: "String Manipulation"
section: "5.6.10"
source: "fhirpath/functions.json"
---
# FHIRPath Function: matches
Returns `true` when the value matches the given regular expression. Regular expressions should function consistently, regardless of any culture- and locale-specific settings in the environment, should be case-sensitive, use 'single line' mode and allow Unicode characters.
The start/end of line markers `^`, `$` can be used to match the entire string.

If the input collection or `regex` are empty, the result is empty (`{ }`).

If the input collection contains multiple items, the evaluation of the expression will end and signal an error to the calling environment.

The optional `flags` parameter can be set to:
{:.stu}
* `i` to perform a case-insensitive search (otherwise is case-sensitive)
* `m` - Matches the start and end of each line using ^ and $ (multi-line)<br/>(not only begin/end of string)
{:.stu}

``` fhirpath
'http://fhir.org/guides/cqf/common/Library/FHIR-ModelInfo|4.0.1'.matches('Library') // returns true
'N8000123123'.matches('^N[0-9]{8}$') // returns false as the string is not an 8 char number (it has 10)
'N8000123123'.matches('N[0-9]{8}') // returns true as the string has an 8 number sequence in it starting with `N`
```
## Summary
- **Category**: String Manipulation
- **Section**: `5.6.10`
- **Return Type**: `Boolean`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `true`
## Description
Returns `true` when the value matches the given regular expression. Regular expressions should function consistently, regardless of any culture- and locale-specific settings in the environment.
## Arguments
- `regex`: `String` - Regular expression to match against
- `flags` (optional): `String` - Optional flags for the regex (i for case-insensitive, m for multi-line)
## Type Mapping
- `String-Boolean`
## Example
```fhirpath
'http://fhir.org/guides/cqf/common/Library/FHIR-ModelInfo|4.0.1'.matches('Library') // returns true
'N8000123123'.matches('^N[0-9]{8}$') // returns false as the string is not an 8 char number (it has 10)
```