Php高手进!这个源码查看器怎么错了！

<?php
echo '<title>源码查看器</title>';
echo "源码查看器";
echo '<form action="ymck.php" method="post">网址：<input type="text" name="url" />
<input type="radio" name="str" value = "UTF-8">UTF-8
<input type="radio" name="str" value = "GB2312">GB2312
<input type="hidden" name="id" />
<input type="submit" value="查看" />
</form>';=["id"];
=["str"];
=["url"];
if(!=NULL)
{
=fopen(,"r");
if(==NULL)
echo "获取源码错误";
else 
echo htmlspecialchars(,;
}
?>