PHP regular expression email verification sample code

正则表达式(regular expression)描述了一种字符串匹配的模式（pattern），可以用来检查一个串是否含有某种子串、将匹配的子串替换或者从某个串中取出符合某个条件的子串等。这篇文章主要介绍了PHP正则验证Email的方法,涉及php正则表达式验证的相关技巧,需要的朋友可以参考下。具体如下：

<?php
function validateEmail($email)
{
 $isValid = true;
 $atIndex = strrpos($email, "@");
 if (is_bool($atIndex) && !$atIndex)
 {
  $isValid = false;
 }
 else
 {
  $domain = substr($email, $atIndex+1);
  $local = substr($email, 0, $atIndex);
  $localLen = strlen($local);
  $domainLen = strlen($domain);
  if ($localLen < 1 || $localLen > 64)
  {
   // local part length exceeded
   $isValid = false;
  }
  else if ($domainLen < 1 || $domainLen > 255)
  {
   // domain part length exceeded
   $isValid = false;
  }
  else if ($local[0] == &#39;.&#39; || $local[$localLen-1] == &#39;.&#39;)
  {
   // local part starts or ends with &#39;.&#39;
   $isValid = false;
  }
  else if (preg_match(&#39;/\\.\\./&#39;, $local))
  {
   // local part has two consecutive dots
   $isValid = false;
  }
  else if (!preg_match(&#39;/^[A-Za-z0-9\\-\\.]+$/&#39;, $domain))
  {
   // character not valid in domain part
   $isValid = false;
  }
  else if (preg_match(&#39;/\\.\\./&#39;, $domain))
  {
   // domain part has two consecutive dots
   $isValid = false;
  }
  else if(!preg_match(&#39;/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\&#39;*+?^{}|~.-])+$/&#39;, str_replace("\\\\","",$local)))
  {
   // character not valid in local part unless 
   // local part is quoted
   if (!preg_match(&#39;/^"(\\\\"|[^"])+"$/&#39;, str_replace("\\\\","",$local)))
   {
   $isValid = false;
   }
  }
  if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A")))
  {
   // domain not found in DNS
   $isValid = false;
  }
 }
 return $isValid;
}
?>

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