Implementation and detailed explanation of regular expression of email address in PHP

Attach the code first
Copy the code The code is as follows:
^[_.0-9a-z-]+@([0-9a-z][0-9a-z-]+.)+[a-z]{2 ,3}$

In this regular expression, "+" means that the previous string appears one or more consecutively; "^" means that the next string must appear at the beginning, and "$" means the previous string Must appear at the end;
"." is also ".", where "" is the escape character; "{2,3}" means that the previous string can appear 2-3 times in a row. "()" means that the contained content must also appear in the target object. "[_.0-9a-z-]" means any character contained in "_", ".", "-", letters in the range from a to z, and numbers in the range from 0 to 9;
In this way, this regular expression can be translated like this:
"The following characters must be at the beginning (^)", "The characters must be contained in "_", ".", "-", from a to z Letters, numbers in the range from 0 to 9 ([_.0-9a-z-])", "The preceding character appears at least once (+)", @, "The string consists of a string from a to Starting with a letter in the range z, a number in the range 0 to 9, followed by at least one character contained in "-", any letter in the range a to z, any number in the range 0 to 9 characters, ending with . (([0-9a-z][0-9a-z-]+.))", "The previous character appears at least once (+)", "from a to z The letter appears 2-3 times and ends with it ([a-z]{2,3}$)"
Copy code The code is as follows:
function is_valid_email($email, $test_mx = false)
{
if(eregi("^ ([_a-z0-9-]+)(.[_a-z0-9-]+)*@([a-z0-9-]+)(.[a-z0-9-]+)*( .[a-z]{2,4})[ wind_phpcode_0 ]quot;, $email))
if($test_mx)
{
list($username, $domain) = split("@", $email);
return getmxrr($domain, $mxrecords);
}
else
return true;
else
return false;
}

The domain name consists of the specific character set of each country's language, English letters, numbers and "-" (i.e. hyphen or minus ), but cannot contain "-" at the beginning or end, and "-" cannot appear consecutively. The letters in the domain name are not case-sensitive. The domain name can be up to 60 bytes (including the suffix .com, .net). , .org, etc.).
/^[a-z]([a-z0-9]*[-_]?[a-z0-9]+)*@([a-z0-9]*[-_] ?[a-z0-9]+)+[.][a-z]{2,3}([.][a-z]{2})?$/i;
/content/i constitutes a case-insensitive Regular expression;
^ Start of match

$ End of match

[a-z] E-Mail prefix must start with an English letter

([a-z0-9]*[-_]?[a-z0-9 ]+)* matches _a_2, aaa11, _1_a_2, but does not match a1_, aaff_33a_, a__aa. If it is a null character, it will also match. * means 0 or more.

* represents 0 or more previous characters.

[a-z0-9]* matches 0 or more English letters or numbers

[-_]? matches 0 or 1 "-", because "-" cannot appear continuously

[a-z0-9]+ matches one or more English letters or numbers, because "-" cannot be used as the end

@ There must be @

([a-z0 -9]*[-_]?[a-z0-9]+)+ See the explanation above ([a-z0-9]*[-_]?[a-z0-9]+)*, but it cannot be Empty, + means one or multiple.

[.] treats special characters (.) as ordinary characters

[a-z]{2,3} matches 2 to 3 English letters, usually com or net, etc.

([.][a-z]{ 2})? Matches 0 or 1 [.][a-z]{2} (such as .cn, etc.) I don’t know if the last part of .com.cn is usually two digits. If not, please modify {2 } is {number of starting words, number of ending words}

Perfect E-Mail regular expression, with detailed explanation, please help test it! 2. Extract email from the string:
Copy code The code is as follows:
function getEmail($str) {
$pattern = "/([a-z0-9]*[-_.]?[ a-z0-9]+)*@([a-z0-9]*[-_]?[a-z0-9]+)+[.][a-z]{2,3}([.][ a-z]{2})?/i";
preg_match_all($pattern,$str,$emailArr);
return $emailArr[0];
}
$emailstr = "9999@qq.com.cn俺not米vi Open the iid mailing list locally: fuyongjie@163.com and hh@qq.com;, fuyongjie.100@yahoo.com, fu-1999@sina.com";
$emailArr = getEmail($emailstr);
echo "

"; <br>print_r($emailArr); <br>echo "

";
?>Print as follows:
Array
(
[0] =>9999@qq.com. cn
[1] =>fuyongjie@163.com
[2] =>hh@qq.com
[3] =>fuyongjie.100@yahoo.com
[4] =>fu-1999@ sina.com
) 3. Comparison: The ^ and $ in the 1st are not included in the regular expression in the 2nd one;

Look at the example again
Copy the code The code is as follows:
function funcemail($str)//Mailbox regular expression
{
return (preg_match('/^[_.0-9a-z-a-z-]+@([0-9a-z][0-9a-z-]+.)+[a-z]{2,4}$/ ',$str))?true:false;
}//Verification method one
$str="qbcd@126.com.cn";
preg_match("/^[0-9a-z]+@(([0-9a-z]+)[.])+[a-z]{2,3}$/",$str,$re);
print_r($re);//Email verification two
if (eregi("^[_.0-9a-z-]+@([0-9a-z][0-9a-z-]+.)+ [a-z]{2,3}$",$email)) {
echo "Your email has passed the preliminary check";
}//The third email verification method

if (ereg("/^[a-z ]([a-z0-9]*[-_.]?[a-z0-9]+)*@([a-z0-9]*[-_]?[a-z0-9]+) +[.][a-z]{2,3}([.][a-z]{2})?$/i; ",$email)){
echo "your email address is correct!";}
　 else{
echo "please try again!";
}