学习并理解以下几个php 全局变量的用法。

1，$_SERVER["QUERY_STRING"]
说明：查询(query)的字符串

2，$_SERVER["REQUEST_URI"]
说明：访问此页面所需的URI

3，$_SERVER["SCRIPT_NAME"]
说明：包含当前脚本的路径

4，$_SERVER["PHP_SELF"]
说明：当前正在执行脚本的文件名

实例：
1，http://www./ (直接打开主页)
结果：
 

2，http://www. /?p=222 (附带查询)
结果：
 

3，http://www. /index.php?p=222&q=xxx
结果：
 

$_SERVER["QUERY_STRING"]获取查询语句，实例中可知，获取的是?后面的值
$_SERVER["REQUEST_URI"] 获取http://www.xxx.com后面的值，包括/
$_SERVER["SCRIPT_NAME"] 获取当前脚本的路径，如：index.php
$_SERVER["PHP_SELF"] 当前正在执行脚本的文件名

当前url："http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF']

总结：对于QUERY_STRING，REQUEST_URI，SCRIPT_NAME和PHP_SELF，深入了解有利于在$_SERVER函数中正确调用这四个值。

PHP 下载远程文件类，使用HTTP 协议下载文件。
HTTP1.1协议必须指定文档结束后关闭链接，否则读取文档时无法使用feof判断结束。

本类支持断点续传下载。

完整代码如下：

<?php
/**
 * 下载远程文件类 支持断点续传 
 * edit by www.
 */
class HttpDownload {
 private $m_url = "";
  private $m_urlpath = "";
  private $m_scheme = "http";
  private $m_host = "";
  private $m_port = "80";
  private $m_user = "";
  private $m_pass = "";
  private $m_path = "/";
  private $m_query = "";
  private $m_fp = "";
  private $m_error = "";
 private $m_httphead = "" ;
 private $m_html = "";
 
 /**
  * 初始化 
  */
 public function PrivateInit($url){
  $urls = "";
  $urls = @parse_url(/blog_article/$url/index.html);
  $this->m_url = $url;
  if(is_array($urls)) {
   $this->m_host = $urls["host"];
   if(!empty($urls["scheme"])) $this->m_scheme = $urls["scheme"];
   if(!empty($urls["user"])) $this->m_user = $urls["user"];
      if(!empty($urls["pass"])) $this->m_pass = $urls["pass"];
      if(!empty($urls["port"])) $this->m_port = $urls["port"];
      if(!empty($urls["path"])) $this->m_path = $urls["path"];
      $this->m_urlpath = $this->m_path;
   if(!empty($urls["query"])) {
        $this->m_query = $urls["query"];
        $this->m_urlpath .= "?".$this->m_query;
       }
    }
 }
 
 /**
 * 打开指定网址
 */
 function OpenUrl($url) {
  #重设各参数
  $this->m_url = "";
  $this->m_urlpath = "";
  $this->m_scheme = "http";
  $this->m_host = "";
  $this->m_port = "80";
  $this->m_user = "";
  $this->m_pass = "";
  $this->m_path = "/";
  $this->m_query = "";
  $this->m_error = "";
  $this->m_httphead = "" ;
  $this->m_html = "";
  $this->Close();
  #初始化系统
  $this->PrivateInit($url);
  $this->PrivateStartSession();
 }

 /**
 * 获得某操作错误的原因
 */
 public function printError() {
  echo "错误信息：".$this->m_error;
  echo "具体返回头：<br>";
  foreach($this->m_httphead as $k=>$v) { 
   echo "$k => $v <br>\r\n"; 
  }
 }
 
 /**
 * 判别用Get方法发送的头的应答结果是否正确
 */
 public function IsGetOK() {
  if( ereg("^2",$this->GetHead("http-state")) ) { 
   return true; 
  } else {
   $this->m_error .= $this->GetHead("http-state")." - ".$this->GetHead("http-describe")."<br>";
   return false;
  }
 }
 
 /**
 * 看看返回的网页是否是text类型
 */
 public function IsText() {
  if (ereg("^2",$this->GetHead("http-state")) && eregi("^text",$this->GetHead("content-type"))) { 
   return true; 
  } else {
   $this->m_error .= "内容为非文本类型<br>";
   return false;
  }
 }
 /**
 * 判断返回的网页是否是特定的类型
 */
 public function IsContentType($ctype) {
  if (ereg("^2",$this->GetHead("http-state")) && $this->GetHead("content-type") == strtolower()($ctype)) { 
   return true; 
  } else {
   $this->m_error .= "类型不对 ".$this->GetHead("content-type")."<br>";
   return false;
  }
 }
 
 /**
 * 用 HTTP 协议下载文件
 */
 public function SaveToBin($savefilename) {
  if (!$this->IsGetOK()) return false;
  if (@feof($this->m_fp)) { 
   $this->m_error = "连接已经关闭！"; 
   return false; 
  }
  $fp = fopen($savefilename,"w") or die("写入文件 $savefilename 失败！");
  while (!feof($this->m_fp)) {
   @fwrite($fp,fgets($this->m_fp,256));
  }
  @fclose($this->m_fp);
  return true;
 }
 
 /**
 * 保存网页内容为 Text 文件
 */
 public function SaveToText($savefilename) {
  if ($this->IsText()) {
   $this->SaveBinFile($savefilename);
  } else {
   return "";
  }
 }
 
 /**
 * 用 HTTP 协议获得一个网页的内容
 */
 public function GetHtml() {
  if (!$this->IsText()) return "";
  if ($this->m_html!="") return $this->m_html;
  if (!$this->m_fp||@feof($this->m_fp)) return "";
  while(!feof($this->m_fp)) {
   $this->m_html .= fgets($this->m_fp,256);
  }
  @fclose($this->m_fp);
  return $this->m_html;
 }
 
 /**
 * 开始 HTTP 会话
 */
 public function PrivateStartSession() {
  if (!$this->PrivateOpenHost()) {
   $this->m_error .= "打开远程主机出错!";
   return false;
  }
  if ($this->GetHead("http-edition")=="HTTP/1.1") {
   $httpv = "HTTP/1.1";
  } else {
   $httpv = "HTTP/1.0";
  }
  fputs($this->m_fp,"GET ".$this->m_urlpath." $httpv\r\n");
  fputs($this->m_fp,"Host: ".$this->m_host."\r\n");
  fputs($this->m_fp,"Accept: */*\r\n");
  fputs($this->m_fp,"User-Agent: Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.2)\r\n");
  #HTTP1.1协议必须指定文档结束后关闭链接,否则读取文档时无法使用feof判断结束
  if ($httpv=="HTTP/1.1") {
   fputs($this->m_fp,"Connection: Close\r\n\r\n");
  } else {
   fputs($this->m_fp,"\r\n");
  }
  $httpstas = fgets($this->m_fp,256);
  $httpstas = split(" ",$httpstas);
  $this->m_httphead["http-edition"] = trim($httpstas[0]);
  $this->m_httphead["http-state"] = trim($httpstas[1]);
  $this->m_httphead["http-describe"] = "";
  for ($i=2;$i<count($httpstas);$i++) {
   $this->m_httphead["http-describe"] .= " ".trim($httpstas[$i]);
  }
  while (!feof($this->m_fp)) {
   $line = str_replace()("\"","",trim(fgets($this->m_fp,256)));
   if($line == "") break;
   if (ereg(":",$line)) {
    $lines = split(":",$line);
    $this->m_httphead[strtolower(trim($lines[0]))] = trim($lines[1]);
   }
  }
 }
 
 /**
 * 获得一个Http头的值
 */
 public function GetHead($headname) {
  $headname = strtolower($headname);
  if (isset()($this->m_httphead[$headname])) {
   return $this->m_httphead[$headname];
  } else {
   return "";
  }
 }
 
 /**
 * 打开连接
 */
 public function PrivateOpenHost() {
  if ($this->m_host=="") return false;
  $this->m_fp = @fsockopen($this->m_host, $this->m_port, &$errno, &$errstr,10);
  if (!$this->m_fp){
   $this->m_error = $errstr;
   return false;
  } else {
   return true;
  }
 }
 
 /**
 * 关闭连接
 */
 public function Close(){
  @fclose($this->m_fp);
 }
}

//调用示例
#示例1，打开网页
$httpdown = new HttpDownload();
$httpdown->OpenUrl("http://www.");
echo $httpdown->GetHtml();
$httpdown->Close();

#示例2，下载文件
$file = new HttpDownload(); # 实例化类
$file->OpenUrl("http://www./test.pdf"); # 远程文件地址
$file->SaveToBin("test.pdf"); # 保存路径及文件名
$file->Close(); # 释放资源
?>

php文件下载函数分享，代码如下：

<?php
/**
* 文件下载函数举例
* func: down_file
* param: $file
* edit by www.
*/
function down_file($file){
    //First, see if the file exists
    if (!is_file($file)) { die("<b>404 File not found!</b>"); }

    //Gather relevent info about file
    $len = filesize($file);
    $filename = basename($file);
    $file_extension = strtolower(substr(strrchr($filename,"."),1));

    //This will set the Content-Type to the appropriate setting for the file
    switch( $file_extension ) {
          case "pdf": $ctype="application/pdf"; break;
      case "exe": $ctype="application/octet-stream"; break;
      case "zip": $ctype="application/zip"; break;
      case "doc": $ctype="application/msword"; break;
      case "xls": $ctype="application/vnd.ms-excel"; break;
      case "ppt": $ctype="application/vnd.ms-powerpoint"; break;
      case "gif": $ctype="image/gif"; break;
      case "png": $ctype="image/png"; break;
      case "jpeg":
      case "jpg": $ctype="image/jpg"; break;
      case "mp3": $ctype="audio/mpeg"; break;
      case "wav": $ctype="audio/x-wav"; break;
      case "mpeg":
      case "mpg":
      case "mpe": $ctype="video/mpeg"; break;
      case "mov": $ctype="video/quicktime"; break;
      case "avi": $ctype="video/x-msvideo"; break;

      //The following are for extensions that shouldn't be downloaded (sensitive stuff, like php files)
      case "php":
      case "htm":
      case "html":
      case "txt": die("<b>Cannot be used for ". $file_extension ." files!</b>"); break;

      default: $ctype="application/force-download";
    }

    //Begin writing headers
    header("Pragma: public");
    header("Expires: 0");
    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
    header("Cache-Control: public"); 
    header("Content-Description: File Transfer");
    
    //Use the switch-generated Content-Type
    header("Content-Type: $ctype");

    //Force the download
    $header="Content-Disposition: attachment; filename=".$filename.";";
    header($header );
    header("Content-Transfer-Encoding: binary");
    header("Content-Length: ".$len);
    @readfile($file);
    exit;
}
?>