Php regular expression for determining email addresses

Judge a regular expression of the email and explain the meaning of the regular expression one by one.

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 the string header

(W + (-w +) | (. w +) *) 1: match strings such as laidfj456, sfi-lsoke, and fe.23i.

+ Match the plus sign

W + (-w +) | (. w +) * same as 1

@ Matched @

[A-Za-z0-9] + 2: consisting of upper and lower case letters and numbers? Is equivalent to w +.

(. |-) [A-Za-z0-9] +) * matches 0 or multiple strings starting with "." or "-", such as. oeiu234mJ,-oiwuer4

. Match "."

[A-Za-z0-9] + same 2

$ Matching string? Tail

Instance

The code is as follows:

Copy code

<? Php /** * Regular expression @ author: lijianghai */ Function isEmail ($ input = null) {// Username: composed of numbers, letters, and strip; $ Email = $ input; /* Use preg_ereg () error: because the second parameter needs to be an array * If (preg_grep ("^ [a-zA-Z] [a-zA-Z0-9 _] {} @ [0-9A-Za-z }(.) (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 _] {} @ [0-9a-zA-Z }(.) (com | cn | com.cn | net) $ ", $ email ))   { Echo $ email. "compliant with the format specifications ";   } Else   { Echo $ email. 'Format error ';   }  } $ Email = ""; IsEmail ($ email ); ?>