这篇随笔是对预定义数组变量的总结。通过预定义数组变量，我们可以获得系统环境、用户对话、表单数据等信息。
1.服务器变量：$_SERVER
利用foreach语句打印$_SERVER中的所有元素：
<span> <?<span php><span> <span foreach>(<span> <span as> <span> => <span><span><span> <span echo> <span>.' => '.<span>.'<br>'<span><span> <span><span> ?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
2.环境变量: $_ENV(无输出结果)
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3.GET变量:$_GET
<span> <form action="<?<span>['PHP_SELF']?>" method="GET"> <span> 姓名:<input type="text" name="name" size="15"/> <span> 年龄:<input type="text" name="age" size="15"/> <span> 爱好:<input type="text" name="hobby" size="15"/> <span> <input type="submit" name="submit" value="提交"/> <span> </form> <span> <?<span php><span> <span if>(<span isset>(<span>['submit'<span><span> <span echo> '<p>'<span><span> <span echo> '姓名:'.<span>['name'].'<br>'<span><span> <span echo> '年龄:'.<span>['age'].'<br>'<span><span> <span echo> '爱好:'.<span>['hobby'].'<br>'<span><span> <span><span> ?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
4.POST变量:$_POST
通过POST方式传递数据时，数据不会显示在URL中，因此相比GET方式更安全。而且，POST方式传递的数据量理论上没有限制。
<span> <form action="<?<span>['PHP_SELF']?>" method="POST"> <span> 姓名:<input type="text" name="name" size="15"/> <span> 年龄:<input type="text" name="age" size="15"/> <span> 爱好:<input type="text" name="hobby" size="15"/> <span> <input type="submit" name="submit" value="提交"/> <span> </form> <span> <?<span php><span> <span if>(<span isset>(<span>['submit'<span><span> <span echo> '<p>'<span><span> <span echo> '姓名:'.<span>['name'].'<br>'<span><span> <span echo> '年龄:'.<span>['age'].'<br>'<span><span> <span echo> '爱好:'.<span>['hobby'].'<br>'<span><span> <span><span> ?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
5.文件上传变量:$_FILES(代码提示有误，无法找到上传文件)
<span> <form enctype="multipart/form-data" action="<?=<span>['PHP_SELF']?>" method="POST"> <span> <input type="hidden" name="MAX_FILE_SIZE" value="104857600" /><!--100M --> <span> 上传文件:<input name="upload_file" type="file" size="50"/> <span> <input type="submit" name="submit" value="上传" /> <span> </form> <span> <?<span php><span> <span if>(<span isset>(<span>['submit'<span><span> <span echo> <span>['uplaod_file']['error']==UPLOAD_ERR_OK ? '上传成功!<br>': '上传失败！<br>'<span><span> <span echo> '上传文件名:'.<span>['upload_file']['name'].'<br>'<span><span> <span echo> '上传文件大小:'.<span>['upload_file']['size'].'字节<br>'<span><span> <span echo> '临时文件名:'.<span>['upload_file']['tmp_name'].'<br>'<span><span> <span><span> ?></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
