What is the regular expression for validating email addresses?

Validating email addresses using regular expressions (RegEx) can be tricky because of the complexity of allowed characters and domain names. However, a commonly used and reasonably effective RegEx for email validation is:

^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$

Let's break down what each part of this expression means:

• ^: Asserts the start of the string.
• [a-zA-Z0-9._%+-]+: Matches one or more occurrences of:
  • a-z: Lowercase letters
  • A-Z: Uppercase letters
  • 0-9: Digits
  • ., _, %, +, -: Allowed special characters
• @: Matches the at symbol.
• [a-zA-Z0-9.-]+: Matches one or more occurrences of:
  • a-z: Lowercase letters
  • A-Z: Uppercase letters
  • 0-9: Digits
  • ., -: Allowed characters in domain names
• \.: Matches the dot before the top-level domain (escaped to match the character literally).
• [a-zA-Z]{2,}: Matches two or more uppercase or lowercase letters for the top-level domain (like .com, .org, .net).
• $: Asserts the end of the string.

Important Considerations:

• Not Perfect: This RegEx is widely used, but it doesn't cover every edge case and variation of valid email addresses. It is a good balance between simplicity and usefulness.
• Server-Side Verification: It’s always best to perform email verification server-side as well. This often includes sending a verification email to the address provided to ensure it's real and active.
• Complex Emails: Very complex and unusual emails might not be fully validated by this expression. For stricter validation, more complex regex might be required.
• Non-ASCII Domains: This regex does not handle non-ASCII domain names, if you need to support internationalized domain names (IDNs), the regular expression becomes far more complex.

Example of usage in JavaScript:

const emailRegex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
function validateEmail(email) {
  return emailRegex.test(email);
}
console.log(validateEmail("test@example.com")); // Output: true
console.log(validateEmail("invalid-email")); // Output: false


In summary, while the provided regular expression is a good starting point, always remember to complement it with server-side validation and consider your specific use case.

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