PHP to determine the regular expression of e-mail address _php tutorial

In PHP we often use regular expressions to verify that the user entered the information is not the e-mail address, let me introduce you to determine the e-mail address of the regular expression of the detailed

Judge a regular expression of a message, step-by-step to explain what it means

The code is as follows	Copy Code
^ (w+ ((-w+) | (. w+)) +w+ ((-w+) | (. w+)) *@[a-za-z0-9]+ ((. | -) [a-za-z0-9]+] *. [a-za-z0-9]+$

^ Match string header

(w+ (-w+) | (. w+)) 1: This matches the string laidfj456, Sfi-lsoke, fe.23i, and so on

+ Match Plus

w+ ((-w+) | (. w+)) * Same as 1

Match

[a-za-z0-9]+ 2: A string of uppercase and lowercase letters and numbers, equivalent to w+

((.| -) [a-za-z0-9]+] * matches 0 or more by "." Or "-" begins with a string, such as. OEIU234MJ,-oiwuer4

. Match "."

[A-za-z0-9]+ with 2

$ matches the string's tail

Instance

The code is as follows

Copy Code

/** * Regular Expressions for messages @author: Lijianghai */ function Isemail ($input = null) {//username: composed of numbers, letters and slides; $email = $input; /* error using Preg_ereg (): Because the second parameter needs to be an array * IF (Preg_grep ("^[a-za-z][a-za-z0-9_]{3,19}@[0-9a-za-z]{1,10} (.) (com|cn|net|com.cn) $ ", Array ($input))) { echo $email. ' is a qualified email address '; }else { echo $email. ' Format error '; } */ if (Ereg ("^[a-za-z][a-za-z0-9_]{3,9}@[0-9a-za-z]{1,10} (.) (com|cn|com.cn|net) $ ", $email)) { echo $email. " Conforming to the format specification "; } Else { echo $email. ' Format error '; } } $email = ""; Isemail ($email); ?>

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