PHP uses post method to obtain file extension, _PHP tutorial

<form action="" method="post">
    <input type="file" value="" name="file" size="20">
    <input type="submit" value="check">
</form>
<?<span>php
    </span><span>header</span>("Content-type:text/html;charse=utf8"<span>);
    </span><span>if</span>(<span>isset</span>(<span>$_POST</span>['file'<span>])){
        </span><span>$pic</span> = <span>$_POST</span>['file'<span>];
        </span><span>$pics</span> = <span>explode</span>(".", <span>$pic</span><span>);
        </span><span>echo</span> "上传文件的扩展名为：".<span>$pics</span>[<span>count</span>(<span>$pics</span>)-1<span>];        
    }
</span>?>