PHP Form Validation

$errors = [];

$name  = trim($_POST['name']  ?? '');
$email = trim($_POST['email'] ?? '');
$url   = trim($_POST['url']   ?? '');

if ($name === '') {
    $errors['name'] = 'Name is required';
} elseif (strlen($name) > 80) {
    $errors['name'] = 'Name must be 80 characters or less';
}

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $errors['email'] = 'Invalid email';
}

if ($url !== '' && !filter_var($url, FILTER_VALIDATE_URL)) {
    $errors['url'] = 'Invalid URL';
}

if (empty($errors)) {
    // save and redirect
} else {
    // re-render form with errors
}

<input name="email" value="<?= htmlspecialchars($email) ?>">
<?php if (isset($errors['email'])): ?>
    <p class="err"><?= htmlspecialchars($errors['email']) ?></p>
<?php endif; ?>

<?php
$errors = [];
$name  = trim($_POST['name']  ?? '');
$email = trim($_POST['email'] ?? '');
if ($name === '')                                $errors[] = 'Name required';
if (!filter_var($email, FILTER_VALIDATE_EMAIL))  $errors[] = 'Invalid email';
print_r($errors);