PHP：如何验证$ _POST变量？ [重复]

I have the following code:

<?php
$email = $_POST['email'];
if ($email!=='ThisMail'){
header ('Location:http://www.mywebsite.com/');
$handle = fopen("data.txt", "a");
foreach($_POST as $variable => $value) {
   fwrite($handle, $variable);
   fwrite($handle, "=");
   fwrite($handle, $value);
   fwrite($handle, "
");
}
fwrite($handle, "
");
fclose($handle);
exit;
}
else{
header ('Location:http://www.google.com/');
exit;
}
?> 

I am basically collecting information from a form on my website, with action=form.php (where this code is saved). I want it so that if the email field on my HTML document where the form is is filled out with a particular email address, ThisMail, it will write all the stored data from the form in the file data.txt and redirect to the webpage I want.

The other side of the if statement simply redirects the user to another page.

This does not seem to be working for me. How can I fix this?

</div>

Here, $email is not defined, so you should add this before the if statement:

$email = $_POST['email']; // here 'email' is the field name in your HTML page