Flutter & Dart: Regular Expression Examples

A few examples of regular expression and the RegExp class in Flutter and Dart.

Example 1: Email Validation

The code:

// kindacode.com
import 'package:flutter/foundation.dart';

void main() {
  RegExp exp = RegExp(
      r"^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$",
      caseSensitive: false);

  // Try it
  String email1 = "[email protected]";
  String email2 = "test@gmail";
  String email3 = "test#gmail.com";

  if (exp.hasMatch(email1)) {
    if (kDebugMode) {
      print("Email1 OK");
    }
  }

  if (exp.hasMatch(email2)) {
    if (kDebugMode) {
      print("Email2 OK");
    }
  }

  if (exp.hasMatch(email3)) {
    if (kDebugMode) {
      print("Email3 OK");
    }
  }
}

Output:

Email1 OK
Email2 OK

Example 2: IP Addresses Validation

The code:

// kindacode.com
import 'package:flutter/foundation.dart';

void main() {
  RegExp ipExp = RegExp(
      r"^(?!0)(?!.*\.$)((1?\d?\d|25[0-5]|2[0-4]\d)(\.|$)){4}$",
      caseSensitive: false,
      multiLine: false);

  // Try it
  // Expectation: true
  if (ipExp.hasMatch('192.168.1.2')) {
    if (kDebugMode) {
      print('192.168.1.2 is valid');
    }
  }

  // Expectation: false
  if (ipExp.hasMatch('192.168.111111.55555')) {
    if (kDebugMode) {
      print('192.168.111111.55555 is valid');
    }
  }
}

Output:

192.168.1.2 is valid

Example 3: URL validation

The code:

// kindacode.com
import 'package:flutter/foundation.dart';

void main() {
  RegExp urlExp = RegExp(
      r"(http|ftp|https)://[\w-]+(\.[\w-]+)+([\w.,@?^=%&:/~+#-]*[\w@?^=%&/~+#-])?");

  String url1 = "https://www.kindacode.com/cat/mobile/flutter/"; // valid

  String url2 = "https://kindacode/cat/mobile/flutter/"; // invalid

  if (urlExp.hasMatch(url1)) {
    if (kDebugMode) {
      print('Url1 looks good!');
    }
  }

  if (urlExp.hasMatch(url2)) {
    if (kDebugMode) {
      print("Url2 looks good!");
    }
  }
}

Output:

Url1 looks good!

Example 4: Domain validation

// kindacode.com
import 'package:flutter/foundation.dart';

void main() {
  RegExp domainExp = RegExp(r"^[a-z0-9]+([\-\.]{1}[a-z0-9]+)*\.[a-z]{2,6}$");

  String domain1 = "www.kindacode.com"; // expected: valid
  String domain2 = "www.amazon.co.uk"; // expected: valid
  String domain3 = "hello world!"; // expected: invalid

  if (domainExp.hasMatch(domain1)) {
    if (kDebugMode) {
      print('domain1 is valid');
    }
  }

  if (domainExp.hasMatch(domain2)) {
    if (kDebugMode) {
      print('domain2 is valid');
    }
  }

  if (domainExp.hasMatch(domain3)) {
    if (kDebugMode) {
      print('domain3 is valid');
    }
  }
}

Output:

domain1 is valid
domain2 is valid

Wrap Up

We’ve reviewed a few examples of using regular expressions in Dart that may be very helpful in many everyday use cases. If you’d like to learn more about Dart and Flutter, take a look at the following articles:

• Flutter: FilteringTextInputFormatter Examples
• Flutter form validation example
• Flutter & SQLite: CRUD Example
• How to create a Filter/Search ListView in Flutter
• Dart: Converting a List to a Map and Vice Versa
• Dart: Sorting Entries of a Map by Its Values

You can also take a tour around our Flutter topic page and Dart topic page to see the latest tutorials and examples.