Tech: Checking the validity of an e-mail address

This is something that, sooner or later, we all have to do. For checking the validity of an e-mail address, the following expression can be used:

^([a-zA-Z0-9])+([\.a-zA-Z0-9_-])*@([a-zA-Z0-9])+(\.[a-zA-Z0-9_-]+)+$

In this article you will find usage examples in PHP 4.3, JavaScript and C# 1.1.

PHP

<?php
$sRegExp = "^([a-zA-Z0-9])+([\.a-zA-Z0-9_-])*@([a-zA-Z0-9])+(\.[a-zA-Z0-9_-]+)+$";
$sTest1 = "test@test.com";
$sTest2 = "test@test@test.test.13234.plouf";
/*
Purpose: Check if an e-mail address is valid or not.
Input:   A string with an e-mail address.
Output:  A boolean (true if valid, false otherwise).
*/
function isEmailValid($sEmail)
{
    global $sRegExp;
    $iComparison = eregi($sRegExp, $sEmail);
    return $iComparison == 1; 
}
/*
Purpose: Uses the isEmailValid() function on the server.
Input:   None.
Output:  None.
*/
function testServer()
{
	global $sTest1, $sTest2;
	$sMessage = "";
	if (isEmailValid($sTest1))
	{
		$sMessage .= "<b>" . $sTest1 . "</b> is valid!";
	}
	else
	{
		$sMessage .= "<b>" . $sTest1 . "</b> is NOT valid!";
	}
	$sMessage .= "<br>";
	if (isEmailValid($sTest2))
	{
		$sMessage .= "<b>" . $sTest2 . "</b> is valid!";
	}
	else
	{
		$sMessage .= "<b>" . $sTest2 . "</b> is NOT valid!";
	}
	echo $sMessage;
}
?>
<html>
<head>
</head>
<body>
<form>
<p><?php testServer();?></p>
</form>
</body>
</html>

JavaScript

<html>
<head>
<script language="JavaScript">
var oRegExp = /^([a-zA-Z0-9])+([\.a-zA-Z0-9_-])*@([a-zA-Z0-9])+(\.[a-zA-Z0-9_-]+)+$/gi;
var sTest1 = "test@test.com";
var sTest2 = "test@test@test.test.13234.plouf";
/*
Purpose: Check if an e-mail address is valid or not.
Input:   A string with an e-mail address.
Output:  A boolean (true if valid, false otherwise).
*/
function isEmailValid(sEmail)
{
    var bComparison = oRegExp.test(sEmail);
    return bComparison; 
}
/*
Purpose: Uses the isEmailValid() function on the client.
Input:   None.
Output:  None.
*/
function testClient()
{
	var sMessage = "";
	if (isEmailValid(sTest1))
	{
		sMessage += sTest1 + " is valid!";
	}
	else
	{
		sMessage += sTest1 + " is NOT valid!";
	}
	sMessage += "\n";
	if (isEmailValid(sTest2))
	{
		sMessage += sTest2 + " is valid!";
	}
	else
	{
		sMessage += sTest2 + " is NOT valid!";
	}
	alert(sMessage);
}
</script>
</head>
<body>
<form>
<p><input type="button" value="Client Side Test" onclick="testClient()"></p>
</form>
</body>
</html>

Tech

"Software is like entropy. It is difficult to grasp, weighs nothing, and obeys the second law of thermodynamics; i.e., it always increases." (Norman R. Augustine)

Checking the validity of an e-mail address

PHP

JavaScript

C#

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