---
title: Regular Expressions
---

Regular expressions are an important tool for defining and testing patterns,
making them useful in a range of policy use cases. Regular expressions enable
specifying and enforcing rules on text data, such as validating input formats
or extracting relevant substrings for further processing.

Rego's regular expression functions use the RE2[^1] standard, known for its
safety and performance features. RE2 avoids slow performance in common cases
making it good for use in performance sensitive environments like policy evaluation.

[^1]: Read more about the [RE2 syntax](https://github.com/google/re2/wiki/Syntax)

Here is a simple rule based on a regular expression:

```rego
email_valid := regex.match(`^[^@]+@[^@]+\.[^@]+$`, "name@example.com")
```

In this example, the `email_valid` will be true as the email matches the pattern.
Also note that the pattern is defined as a raw string, which is a common practice
as it avoids the need to escape special characters[^2].

[^2]: See [non-raw Regex Regal rule](/projects/regal/rules/idiomatic/non-raw-regex-pattern).

While regular expressions are useful in many policies, it's important to
consider performance and readability. For simple string operations, such as
checking for a substring or performing exact matches, Rego's built-in string
matching functions can be faster and easier to read by non-developers.

:::tip
Check out [regex101.com](https://regex101.com/r/ygG2RR/1) and use the RE2
syntax to test your Rego patterns in a visual way.
:::


<BuiltinTable category={"regex"}/>

## Examples

### `match`

`regex.match()` is a commonly used built-in function that checks if a string matches a
given regular expression pattern. The function returns `true` if the string matches the
pattern and `false` otherwise.

Some examples of policy use cases where `regex.match()` might be used include:

- Validating formats, such as ensuring an email address follows a specific pattern or
  checking if a credit card number matches common formats.
- Matching HTTP paths to specific patterns for routing or access control purposes.

:::tip
Check out [regex101.com](https://regex101.com/r/ygG2RR/1) and use the RE2
syntax to test your Rego patterns in a visual way.
:::

<PlaygroundExample dir={require.context('../_examples/regex/match/email')} />

<PlaygroundExample dir={require.context('../_examples/regex/match/paths')} />

<PlaygroundExample dir={require.context('../_examples/regex/match/names')} />

<PlaygroundExample dir={require.context('../_examples/regex/match/case-insensitive')} />


### `template_match`

`regex.template_match()` is an advanced function for matching inputs against
complex patterns. Sometimes, an input string needs to be validated as a series
of distinct components. This function allows you to offer patterns to validate
specific parts of the string separately.

:::warning
Before continuing, make sure your use case is not solved by the simpler
[`regex.match()`](#match)
or
[`glob.match`](/docs/policy-reference/#builtin-glob-globmatch)
functions.

This functions are easier to use and thus less error prone for simpler use cases.
:::

<PlaygroundExample dir={require.context('../_examples/regex/template_match/path_pattern')} />

### `find_all_string_submatch_n`

`regex.find_all_string_submatch_n()` is an advanced function for matching inputs
against patterns with capture groups. This function returns a list matches,
where matches are themselves lists of strings containing the full match followed
by each of the submatches.

:::warning
Before continuing, make sure your use case is not solved by the simpler
[`regex.match()`](#match) function.

This function is easier to use and thus less error prone for simpler use cases.
:::

<PlaygroundExample dir={require.context('../_examples/regex/find_all_string_submatch_n/email_plus_addressing')} />

<PlaygroundExample dir={require.context('../_examples/regex/find_all_string_submatch_n/scope_parsing/')} />

### `globs_match`

`regex.globs_match()` is a less commonly used built-in function that checks if two patterns
overlap. This can be useful when using patterns to define permissions or access control
rules. The function returns `true` if the two patterns overlap and `false` otherwise.

<PlaygroundExample dir={require.context('../_examples/regex/globs_match/role_patterns')} />
