W3School TIY Editor

<!DOCTYPE HTML>  
<html>
<head>
<style>
.error {color: #FF0000;}
</style>
</head>
<body>

<?php
// 定义变量并设置为空值
$nameErr = $emailErr = $genderErr = $websiteErr = "";
$name = $email = $gender = $comment = $website = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
  if (empty($_POST["name"])) {
    $nameErr = "姓名是必填项";
  } else {
    $name = test_input($_POST["name"]);
    // 检查姓名是否只包含字母和空格
    if (!preg_match("/^[a-zA-Z-' ]*$/",$name)) {
      $nameErr = "只允许字母和空格";
    }
  }
  
  if (empty($_POST["email"])) {
    $emailErr = "邮箱是必填项";
  } else {
    $email = test_input($_POST["email"]);
    // 检查邮箱格式是否正确
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
      $emailErr = "无效的邮箱格式";
    }
  }
    
  if (empty($_POST["website"])) {
    $website = "";
  } else {
    $website = test_input($_POST["website"]);
    // 检查URL地址语法是否有效（此正则表达式也允许URL中的破折号）
    if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i",$website)) {
      $websiteErr = "无效的URL";
    }
  }

if (empty($_POST["comment"])) {
    $comment = "";
  } else {
    $comment = test_input($_POST["comment"]);
  }

if (empty($_POST["gender"])) {
    $genderErr = "性别是必填项";
  } else {
    $gender = test_input($_POST["gender"]);
  }
}

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

<h2>PHP 表单验证示例</h2>
<p><span class="error">* 必填字段</span></p>
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">  
  姓名: <input type="text" name="name" value="<?php echo $name;?>">
  <span class="error">* <?php echo $nameErr;?></span>
  <br><br>
  邮箱: <input type="text" name="email" value="<?php echo $email;?>">
  <span class="error">* <?php echo $emailErr;?></span>
  <br><br>
  网站: <input type="text" name="website" value="<?php echo $website;?>">
  <span class="error"><?php echo $websiteErr;?></span>
  <br><br>
  评论: <textarea name="comment" rows="5" cols="40"><?php echo $comment;?>

性别: value="female">女 value="male">男 value="other">其他 *

您的输入："; echo $name; echo "
"; echo $email; echo "
"; echo $website; echo "
"; echo $comment; echo "
"; echo $gender; ?>