How can PHP be used to validate form input fields for a contact form?

To validate form input fields for a contact form in PHP, you can use conditional statements and regular expressions to check if the input meets certain criteria such as being a valid email address or not empty. You can also sanitize the input to prevent any malicious code from being executed. 

// Check if form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Validate name field
    if (empty($_POST["name"])) {
        $nameErr = "Name is required";
    } else {
        $name = test_input($_POST["name"]);
        // Check if name only contains letters and whitespace
        if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
            $nameErr = "Only letters and white space allowed";
        }
    }

    // Validate email field
    if (empty($_POST["email"])) {
        $emailErr = "Email is required";
    } else {
        $email = test_input($_POST["email"]);
        // Check if email address is well-formed
        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
            $emailErr = "Invalid email format";
        }
    }

    // Additional validation for other fields can be added here

}

function test_input($data) {
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
}

Keywords

PHP form validation input fields contact form error handling

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