php 

filter a var 

$email_a = ‘joe@example.com‘;
$email_b = ‘bogus‘;

if (filter_var($email_a, FILTER_VALIDATE_EMAIL)) {
 echo "Cette ($email_a) adresse email est considérée comme valide.";
}
if (filter_var($email_b, FILTER_VALIDATE_EMAIL)) {
 echo "Cette ($email_b) adresse email est considérée comme valide.";
}

php filter by key