Alphanumeric Validation Regular Expression

Alphanumeric validation ensures that input contains only letters (A-Z, a-z) and digits (0-9). This is commonly used for usernames, identifiers, product codes, and other fields where only basic ASCII letters and numbers are permitted. The pattern strictly validates ASCII characters and does not support Unicode letters, accented characters, or special symbols.

Recommended Solution

^[a-zA-Z0-9]+$

Explanation

^ - Start of the string.
[a-zA-Z0-9]+ - Matches one or more characters that are either uppercase letters (A-Z), lowercase letters (a-z), or digits (0-9).
$ - End of the string.

Note: This pattern uses ASCII character ranges and does not support Unicode characters. If you need to support international characters (e.g., ñ, é, 你, Ж), consider using Unicode character classes like \p{L} and \p{N} where supported, or a more permissive pattern.

Implementation

const alphanumericRegex = /^[a-zA-Z0-9]+$/;
const isValidAlphanumeric = (input) => alphanumericRegex.test(input);

import re

def is_valid_alphanumeric(input):
  alphanumericRegex = r"^[a-zA-Z0-9]+$"
  return re.match(alphanumericRegex, input) is not None

use regex::Regex;

fn is_valid_alphanumeric(input: &str) -> bool {
  let alphanumericRegex = Regex::new("^[a-zA-Z0-9]+$")
    .expect("Could not parse alphanumeric validation regex");
  alphanumericRegex.is_match(input)
}

package main

import (
  "regexp"
)

func isValidAlphanumeric(input string) bool {
  alphanumericRegex := "^[a-zA-Z0-9]+$"
  re := regexp.MustCompile(alphanumericRegex)
  return re.MatchString(input)
}

import Foundation

func isValidAlphanumeric(_ input: String) -> Bool {
  let alphanumericRegex = "^[a-zA-Z0-9]+$"
  return NSPredicate(format: "SELF MATCHES %@", alphanumericRegex).evaluate(with: input)
}

using System;
using System.Text.RegularExpressions;

class Application {
  static bool IsValidAlphanumeric(string input) {
    string alphanumericRegex = "^[a-zA-Z0-9]+$";
    return Regex.IsMatch(input, alphanumericRegex);
  }
}

import java.util.regex.*;

public class Application {
  public static boolean isValidAlphanumeric(String input) {
    String alphanumericRegex = "^[a-zA-Z0-9]+$";
    Pattern pattern = Pattern.compile(alphanumericRegex);
    Matcher matcher = pattern.matcher(input);
    return matcher.matches();
  }
}

<?php
function isValidAlphanumeric($input) {
  $alphanumericRegex = "^[a-zA-Z0-9]+$";
  return preg_match("/" . $alphanumericRegex . "/", $input);
}
?>

Test Cases

Input	Valid
abc123
ABC
123
Test123
a1b2c3
0
Z
(empty string)
abc-123
abc_123
abc 123
abc.123
abc@123
hello world
test!
user@domain
ñoño
café
你好
привет

With Underscores

For cases where you need to allow underscores in addition to letters and numbers (common for programming identifiers, variable names, or database column names), you can use this extended pattern. This is useful for validating usernames, API keys, or any identifier that follows programming language naming conventions.

^[a-zA-Z0-9_]+$

Explanation

^ - Start of the string.
[a-zA-Z0-9_]+ - Matches one or more characters that are uppercase letters (A-Z), lowercase letters (a-z), digits (0-9), or underscores (_).
$ - End of the string.

Alternative: You can also use the shorthand \w which is equivalent to [a-zA-Z0-9_] in most regex flavors, making the pattern ^\w+$. However, be aware that in some environments (like JavaScript with Unicode flag), \w may match additional Unicode characters.

Implementation

const basicAlphanumericRegex = /^[a-zA-Z0-9_]+$/;
const isValidAlphanumeric = (input) => basicAlphanumericRegex.test(input);

import re

basic_alphanumeric_regex = r'^[a-zA-Z0-9_]+$'

def is_valid_alphanumeric(input):
    return bool(re.match(basic_alphanumeric_regex, input))

use regex::Regex;

fn is_valid_alphanumeric(input: &str) -> bool {
    let re = Regex::new(r"^[a-zA-Z0-9_]+$").unwrap();
    re.is_match(input)
}

package main

import (
    "regexp"
)

func isValidAlphanumeric(input string) bool {
    re := regexp.MustCompile(`^[a-zA-Z0-9_]+$`)
    return re.MatchString(input)
}

import Foundation

func isValidAlphanumeric(_ input: String) -> Bool {
    let regex = try! NSRegularExpression(pattern: "^[a-zA-Z0-9_]+$")
    return regex.firstMatch(in: input, range: NSRange(location: 0, length: input.utf16.count)) != nil
}

using System;
using System.Text.RegularExpressions;

class Program {
    static bool IsValidAlphanumeric(string input) {
        return Regex.IsMatch(input, @"^[a-zA-Z0-9_]+$");
    }
}

import java.util.regex.*;

public class AlphanumericValidator {
    public static boolean isValidAlphanumeric(String input) {
        return Pattern.matches("^[a-zA-Z0-9_]+$", input);
    }
}

<?php
function isValidAlphanumeric($input) {
    return preg_match("/^[a-zA-Z0-9_]+$/", $input);
}

Test Cases

Input	Valid
abc123
ABC
123
Test123
a1b2c3
0
Z
abc_123
user_name_123
TEST_CONSTANT
(empty string)
abc-123
abc 123
abc.123
abc@123
hello world
test!
user@domain
ñoño
café
你好
привет