Validation with regular expression

Validation becomes very important part when we take inputs from user and we need valid and correct values to work on. Here are little piece of codes to validate domain and email which uses regular expression.

Function to validate Domain

  function isValidDomain($domain){
    if (preg_match ("/^[a-z0-9][a-z0-9\-]+[a-z0-9](\.[a-z]{2,4})+$/i",
        $domain)) {
        return true;
    } else {
        return false;
    }
  }

  # Call function

  if (isValidDomain('example.com')) {
    echo 'Valid Domain';
  }else{
    echo 'Invalid Domain';
  }

Domain validation including subdomain

  function isValidSubDomain($domain){
    if (preg_match ('/([a-zA-Z0-9\-_]+\.)?[a-zA-Z0-9\-_]+\.[a-zA-Z]{2,5}/',
        $domain)) {
        return true;
    } else {
        return false;
    }
  }

  # Call function

  if (isValidSubDomain('subdomain.example.com')) {
    echo 'Valid Domain';
  }else{
    echo 'Invalid Domain';
  }

Function to validate Email

  function isValidEmail($email){
    if (preg_match("/^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/i",
        $email)) {
        return true;
    } else {
        return false;
    }
  }
   
  # Call Function

   if (isValidEmail('email@example.com')) {
    echo 'Valid Email';
    }else {
    echo 'Invalid Email';
   }