Rego Built-in Function: regex.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 and use the RE2 syntax to test your Rego patterns in a visual way.

Examples

Pattern email validation

Validating emails with Regular Expressions is a common policy task. Email validation is more complicated than just checking an email matches a pattern, but since a Rego policy is often a first point of contact, doing a pattern based test on emails is still a good idea as it can help surface issues to users early if they make a mistake.

regex.match is the best way to validate emails in Rego.

data.json

{}

input.json

{
  "email": "hello at example.com"
}

policy.rego

package play

import rego.v1

example_email_1 := "foo [at] example.com"

example_email_2 := "foo@example.com"

match_1 := regex.match(`^[^@]+@[^@]+\.[^@]+$`, example_email_1)

match_2 := regex.match(`^[^@]+@[^@]+\.[^@]+$`, example_email_2)

match_3 := regex.match(`^[^@]+@[^@]+\.[^@]+$`, input.email)

Open in OPA Playground

Rule	Output Value	Notes
match_1	false
match_2	true
match_3		Depends on user input

Path-based access

Managing access control in web applications is crucial for security. The following example uses Rego's regex.match to define role-based access to different URL paths. By associating URL patterns with user roles like "intern" and "admin," it ensures that users only access authorized paths.

policy.rego

package play

import rego.v1

news_pattern := `^/news/.*`

admin_pattern := `^/admin/.*`

path_patterns := {
	"intern": {news_pattern},
	"admin": {news_pattern, admin_pattern},
}

default allow := false

allow if {
	some pattern in path_patterns[input.role]
	regex.match(pattern, input.path)
}

input.json

{
  "role": "intern",
  "path": "/admin/staff/123/salary"
}

data.json

{}

Open in OPA Playground

Rule	Output Value	Notes
allow	false	Interns can't access /admin paths.

Validating user text input

Text provided by users is often unstructured and untrusted. To ensure that the data is both safe to use and error-free, regex.match() can be used to validate the data against a simple pattern.

data.json

{}

input.json

{}

policy.rego

package play

import rego.v1

name_pattern := `^(\p{L}+\s?)+\p{L}+$`

valid_name1 := regex.match(name_pattern, "Juan Pérez")

valid_name2 := regex.match(name_pattern, "张伟")

invalid_name1 := regex.match(name_pattern, "Juan ")

invalid_name2 := regex.match(name_pattern, "- 张伟")

Open in OPA Playground

Rule	Output Value	Notes
valid_name1	true
valid_name2	true
invalid_name1	false	This name has a trailing space
invalid_name2	false	This name has - at the start

Case insensitive matching

Sometimes data can be supplied in a variety of cases, and matches need to be the same regardless of case. One example of this when matching GitHub usernames.

This is where the (?i) modifier comes in. In the following example we can see how repos with different cases are matched.

policy.rego

package play

import rego.v1

matching_repos contains repo if {
	some repo, url in input.repos

	regex.match(`(?i)^github.com\/styrainc\/`, url)
}

input.json

{
  "repos": {
    "regal": "github.com/styrainc/regal",
    "demos": "github.com/StyraInc/opa-sdk-demos",
    "enterprise-opa": "github.com/styrainc/enterprise-opa",
    "opa": "github.com/open-policy-agent/opa"
  }
}

data.json

{}

Open in OPA Playground

Rule	Output Value
matching_repos	["demos","enterprise-opa","regal"]

tip

Here are the common modifiers for regular expressions:

Flag	Description
i	case-insensitive (default false)
m	multi-line mode: ^ and $ match begin/end line in addition to begin/end text
s	let . match \n (default false)

Read more here on the RE2 Wiki.