RSS（简易信息聚合，也叫聚合内容）是一种描述和同步网站内容的格式。RSS可以是以下三个解释的其中一个： Really Simple Syndication；RDF (Resource Description Framework) Site Summary； Rich Site Summary。但其实这三个解释都是指同一种Syndication的技术。RSS目前广泛用于网上新闻频道，blog和wiki。使用RSS订阅能更快地获取信息，网站提供RSS输出，有利于让用户获取网站内容的最新更新。网络用户可以在客户端借助于支持RSS的聚合工具软件，在不打开网站内容页面的情况下阅读支持RSS输出的网站内容。

从技术上来说一个RSS文件就是一段规范的XML数据，该文件一般以rss，xml或者rdf作为后缀，下面是一段 rss 文件的内容示例：

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0">
<channel>
<title>php程序员教程网</title>
<link>http://php.hhsy.cc/</link>
<description>本站是一个php程序员的工作生活笔记!</description>
<item>
<title>RSS Tutorial</title>
<link>网站地址/rss</link>
<description>New RSS tutorial on W3School</description>
</item>
<item>
<title>XML Tutorial</title>
<link>网站地址/xml</link>
<description>New XML tutorial on W3School</description>
</item>
</channel>
</rss>

下面分享一段使用 php 动态生成 RSS 的代码示例：

<?php
/**
** php 动态生成 RSS 类
**/
define("TIME_ZONE","");
define("FEEDCREATOR_VERSION","php.hhsy.cc");//您的网址
class FeedItem extends HtmlDescribable{
	var $title,$description,$link;
	var $author,$authorEmail,$image,$category,$comments,$guid,$source,$creator;
	var $date;
	var $additionalElements=Array();
}

class FeedImage extends HtmlDescribable{
	var $title,$url,$link;
	var $width,$height,$description;
}

class HtmlDescribable{
	var $descriptionHtmlSyndicated;
	var $descriptionTruncSize;

	function getDescription(){
		$descriptionField=new FeedHtmlField($this->description);
		$descriptionField->syndicateHtml=$this->descriptionHtmlSyndicated;
		$descriptionField->truncSize=$this->descriptionTruncSize;
		return $descriptionField->output();
	}
}

class FeedHtmlField{
	var $rawFieldContent;
	var $truncSize,$syndicateHtml;
	function FeedHtmlField($parFieldContent){
		if($parFieldContent){
			$this->rawFieldContent=$parFieldContent;
		}
	}
	function output(){
		if(!$this->rawFieldContent){
			$result="";
		}    elseif($this->syndicateHtml){
			$result="<![CDATA[".$this->rawFieldContent."]]>";
		}else{
			if($this->truncSize and is_int($this->truncSize)){
				$result=FeedCreator::iTrunc(htmlspecialchars($this->rawFieldContent),$this->truncSize);
			}else{
				$result=htmlspecialchars($this->rawFieldContent);
			}
		}
		return $result;
	}

}

class UniversalFeedCreator extends FeedCreator{
	var $_feed;

	function _setFormat($format){
		switch (strtoupper($format)){
			case "2.0":
				// fall through
			case "RSS2.0":
				$this->_feed=new RSSCreator20();
				break;
			case "0.91":
				// fall through
			case "RSS0.91":
				$this->_feed=new RSSCreator091();
				break;
			default:
				$this->_feed=new RSSCreator091();
				break;
		}

		$vars=get_object_vars($this);
		foreach ($vars as $key => $value){
			// prevent overwriting of properties "contentType","encoding"; do not copy "_feed" itself
			if(!in_array($key, array("_feed","contentType","encoding"))){
				$this->_feed->{$key}=$this->{$key};
			}
		}
	}

	function createFeed($format="RSS0.91"){
		$this->_setFormat($format);
		return $this->_feed->createFeed();
	}

	function saveFeed($format="RSS0.91",$filename="",$displayContents=true){
		$this->_setFormat($format);
		$this->_feed->saveFeed($filename,$displayContents);
	}

	function useCached($format="RSS0.91",$filename="",$timeout=3600){
		$this->_setFormat($format);
		$this->_feed->useCached($filename,$timeout);
	}

}

class FeedCreator extends HtmlDescribable{
	var $title,$description,$link;
	var $syndicationURL,$image,$language,$copyright,$pubDate,$lastBuildDate,$editor,$editorEmail,$webmaster,$category,$docs,$ttl,$rating,$skipHours,$skipDays;
	var $xslStyleSheet="";
	var $items=Array();
	var $contentType="application/xml";
	var $encoding="utf-8";
	var $additionalElements=Array();

	function addItem($item){
		$this->items[]=$item;
	}

	function clearItem2Null(){
		$this->items=array();
	}

	function iTrunc($string,$length){
		if(strlen($string)<=$length){
			return $string;
		}

		$pos=strrpos($string,".");
		if($pos>=$length-4){
			$string=substr($string,0,$length-4);
			$pos=strrpos($string,".");
		}
		if($pos>=$length*0.4){
			return substr($string,0,$pos+1)." ...";
		}

		$pos=strrpos($string," ");
		if($pos>=$length-4){
			$string=substr($string,0,$length-4);
			$pos=strrpos($string," ");
		}
		if($pos>=$length*0.4){
			return substr($string,0,$pos)." ...";
		}

		return substr($string,0,$length-4)." ...";
	}


	function _createGeneratorComment(){
		return "<!-- generator=\"".FEEDCREATOR_VERSION."\" -->\n";
	}

	function _createAdditionalElements($elements,$indentString=""){
		$ae="";
		if(is_array($elements)){
			foreach($elements AS $key => $value){
				$ae.= $indentString."<$key>$value</$key>\n";
			}
		}
		return $ae;
	}

	function _createStylesheetReferences(){
		$xml="";
		if($this->cssStyleSheet) $xml .= "<?xml-stylesheet href=\"".$this->cssStyleSheet."\" type=\"text/css\"?>\n";
		if($this->xslStyleSheet) $xml .= "<?xml-stylesheet href=\"".$this->xslStyleSheet."\" type=\"text/xsl\"?>\n";
		return $xml;
	}

	function createFeed(){}

	function _generateFilename(){
		$fileInfo=pathinfo($_SERVER["PHP_SELF"]);
		return substr($fileInfo["basename"],0,-(strlen($fileInfo["extension"])+1)).".xml";
	}

	function _redirect($filename){
		Header("Content-Type: ".$this->contentType."; charset=".$this->encoding."; filename=".basename($filename));
		Header("Content-Disposition: inline; filename=".basename($filename));
		readfile($filename,"r");
		die();
	}

	function useCached($filename="",$timeout=3600){
		$this->_timeout=$timeout;
		if($filename==""){
			$filename=$this->_generateFilename();
		}
		if(file_exists($filename) && (time()-filemtime($filename) < $timeout)){
			$this->_redirect($filename);
		}
	}

	function saveFeed($filename="",$displayContents=true){
		if($filename==""){
			$filename=$this->_generateFilename();
		}
		$feedFile=fopen($filename,"w+");
		if($feedFile){
			fputs($feedFile,$this->createFeed());
			fclose($feedFile);
			if($displayContents){
				$this->_redirect($filename);
			}
		}else{
			echo "<br /><b>Error creating feed file, please check write permissions.</b><br />";
		}
	}

}

class FeedDate{
	var $unix;
	function FeedDate($dateString=""){
		if($dateString=="") $dateString=date("r");

		if(is_integer($dateString)){
			$this->unix=$dateString;
			return;
		}
		if(preg_match("~(?:(?:Mon|Tue|Wed|Thu|Fri|Sat|Sun),\\s+)?(\\d{1,2})\\s+([a-zA-Z]{3})\\s+(\\d{4})\\s+(\\d{2}):(\\d{2}):(\\d{2})\\s+(.*)~",$dateString,$matches)){
			$months=Array("Jan"=>1,"Feb"=>2,"Mar"=>3,"Apr"=>4,"May"=>5,"Jun"=>6,"Jul"=>7,"Aug"=>8,"Sep"=>9,"Oct"=>10,"Nov"=>11,"Dec"=>12);
			$this->unix=mktime($matches[4],$matches[5],$matches[6],$months[$matches[2]],$matches[1],$matches[3]);
			if(substr($matches[7],0,1)=='+' OR substr($matches[7],0,1)=='-'){
				$tzOffset=(substr($matches[7],0,3) * 60 + substr($matches[7],-2)) * 60;
			}else{
				if(strlen($matches[7])==1){
					$oneHour=3600;
					$ord=ord($matches[7]);
					if($ord < ord("M")){
						$tzOffset=(ord("A") - $ord - 1) * $oneHour;
					} elseif($ord >= ord("M") && $matches[7]!="Z"){
						$tzOffset=($ord - ord("M")) * $oneHour;
					} elseif($matches[7]=="Z"){
						$tzOffset=0;
					}
				}
				switch ($matches[7]){
					case "UT":
					case "GMT":    $tzOffset=0;
				}
			}
			$this->unix += $tzOffset;
			return;
		}
		if(preg_match("~(\\d{4})-(\\d{2})-(\\d{2})T(\\d{2}):(\\d{2}):(\\d{2})(.*)~",$dateString,$matches)){
			$this->unix=mktime($matches[4],$matches[5],$matches[6],$matches[2],$matches[3],$matches[1]);
			if(substr($matches[7],0,1)=='+' OR substr($matches[7],0,1)=='-'){
				$tzOffset=(substr($matches[7],0,3) * 60 + substr($matches[7],-2)) * 60;
			}else{
				if($matches[7]=="Z"){
					$tzOffset=0;
				}
			}
			$this->unix += $tzOffset;
			return;
		}
		$this->unix=0;
	}

	function rfc822(){
		$date=gmdate("Y-m-d H:i:s",$this->unix);
		if(TIME_ZONE!="") $date .= " ".str_replace(":","",TIME_ZONE);
		return $date;
	}

	function iso8601(){
		$date=gmdate("Y-m-d H:i:s",$this->unix);
		$date=substr($date,0,22) . ':' . substr($date,-2);
		if(TIME_ZONE!="") $date=str_replace("+00:00",TIME_ZONE,$date);
		return $date;
	}

	function unix(){
		return $this->unix;
	}
}

class RSSCreator10 extends FeedCreator{
	function createFeed(){
		$feed="<?xml version=\"1.0\" encoding=\"".$this->encoding."\"?>\n";
		$feed.= $this->_createGeneratorComment();
		if($this->cssStyleSheet==""){
			$cssStyleSheet="http://www.w3.org/2000/08/w3c-synd/style.css";
		}
		$feed.= $this->_createStylesheetReferences();
		$feed.= "<rdf:RDF\n";
		$feed.= "    xmlns=\"http://purl.org/rss/1.0/\"\n";
		$feed.= "    xmlns:rdf=\"http://www.w3.org/1999/02/22-rdf-syntax-ns#\"\n";
		$feed.= "    xmlns:slash=\"http://purl.org/rss/1.0/modules/slash/\"\n";
		$feed.= "    xmlns:dc=\"http://purl.org/dc/elements/1.1/\">\n";
		$feed.= "    <channel rdf:about=\"".$this->syndicationURL."\">\n";
		$feed.= "        <title>".htmlspecialchars($this->title)."</title>\n";
		$feed.= "        <description>".htmlspecialchars($this->description)."</description>\n";
		$feed.= "        <link>".$this->link."</link>\n";
		if($this->image!=null){
			$feed.= "        <image rdf:resource=\"".$this->image->url."\" />\n";
		}
		$now=new FeedDate();
		$feed.= "       <dc:date>".htmlspecialchars($now->iso8601())."</dc:date>\n";
		$feed.= "        <items>\n";
		$feed.= "            <rdf:Seq>\n";
		for ($i=0;$i<count($this->items);$i++){
			$feed.= "                <rdf:li rdf:resource=\"".htmlspecialchars($this->items[$i]->link)."\"/>\n";
		}
		$feed.= "            </rdf:Seq>\n";
		$feed.= "        </items>\n";
		$feed.= "    </channel>\n";
		if($this->image!=null){
			$feed.= "    <image rdf:about=\"".$this->image->url."\">\n";
			$feed.= "        <title>".$this->image->title."</title>\n";
			$feed.= "        <link>".$this->image->link."</link>\n";
			$feed.= "        <url>".$this->image->url."</url>\n";
			$feed.= "    </image>\n";
		}
		$feed.= $this->_createAdditionalElements($this->additionalElements,"    ");

		for ($i=0;$i<count($this->items);$i++){
			$feed.= "    <item rdf:about=\"".htmlspecialchars($this->items[$i]->link)."\">\n";
			//$feed.= "        <dc:type>Posting</dc:type>\n";
			$feed.= "        <dc:format>text/html</dc:format>\n";
			if($this->items[$i]->date!=null){
				$itemDate=new FeedDate($this->items[$i]->date);
				$feed.= "        <dc:date>".htmlspecialchars($itemDate->iso8601())."</dc:date>\n";
			}
			if($this->items[$i]->source!=""){
				$feed.= "        <dc:source>".htmlspecialchars($this->items[$i]->source)."</dc:source>\n";
			}
			if($this->items[$i]->author!=""){
				$feed.= "        <dc:creator>".htmlspecialchars($this->items[$i]->author)."</dc:creator>\n";
			}
			$feed.= "        <title>".htmlspecialchars(strip_tags(strtr($this->items[$i]->title,"\n\r","  ")))."</title>\n";
			$feed.= "        <link>".htmlspecialchars($this->items[$i]->link)."</link>\n";
			$feed.= "        <description>".htmlspecialchars($this->items[$i]->description)."</description>\n";
			$feed.= $this->_createAdditionalElements($this->items[$i]->additionalElements,"        ");
			$feed.= "    </item>\n";
		}
		$feed.= "</rdf:RDF>\n";
		return $feed;
	}
}

class RSSCreator091 extends FeedCreator{
	var $RSSVersion;

	function RSSCreator091(){
		$this->_setRSSVersion("0.91");
		$this->contentType="application/rss+xml";
	}

	function _setRSSVersion($version){
		$this->RSSVersion=$version;
	}

	function createFeed(){
		$feed="<?xml version=\"1.0\" encoding=\"".$this->encoding."\"?>\n";
		$feed.= $this->_createGeneratorComment();
		$feed.= $this->_createStylesheetReferences();
		$feed.= "<rss version=\"".$this->RSSVersion."\">\n";
		$feed.= "    <channel>\n";
		$feed.= "        <title>".FeedCreator::iTrunc(htmlspecialchars($this->title),100)."</title>\n";
		$this->descriptionTruncSize=500;
		$feed.= "        <description>".$this->getDescription()."</description>\n";
		$feed.= "        <link>".$this->link."</link>\n";
		$now=new FeedDate();
		$feed.= "        <lastBuildDate>".htmlspecialchars($now->rfc822())."</lastBuildDate>\n";
		$feed.= "        <generator>".FEEDCREATOR_VERSION."</generator>\n";

		if($this->image!=null){
			$feed.= "        <image>\n";
			$feed.= "            <url>".$this->image->url."</url>\n";
			$feed.= "            <title>".FeedCreator::iTrunc(htmlspecialchars($this->image->title),100)."</title>\n";
			$feed.= "            <link>".$this->image->link."</link>\n";
			if($this->image->width!=""){
				$feed.= "            <width>".$this->image->width."</width>\n";
			}
			if($this->image->height!=""){
				$feed.= "            <height>".$this->image->height."</height>\n";
			}
			if($this->image->description!=""){
				$feed.= "            <description>".$this->image->getDescription()."</description>\n";
			}
			$feed.= "        </image>\n";
		}
		if($this->language!=""){
			$feed.= "        <language>".$this->language."</language>\n";
		}
		if($this->copyright!=""){
			$feed.= "        <copyright>".FeedCreator::iTrunc(htmlspecialchars($this->copyright),100)."</copyright>\n";
		}
		if($this->editor!=""){
			$feed.= "        <managingEditor>".FeedCreator::iTrunc(htmlspecialchars($this->editor),100)."</managingEditor>\n";
		}
		if($this->webmaster!=""){
			$feed.= "        <webMaster>".FeedCreator::iTrunc(htmlspecialchars($this->webmaster),100)."</webMaster>\n";
		}
		if($this->pubDate!=""){
			$pubDate=new FeedDate($this->pubDate);
			$feed.= "        <pubDate>".htmlspecialchars($pubDate->rfc822())."</pubDate>\n";
		}
		if($this->category!=""){
			$feed.= "        <category>".htmlspecialchars($this->category)."</category>\n";
		}
		if($this->docs!=""){
			$feed.= "        <docs>".FeedCreator::iTrunc(htmlspecialchars($this->docs),500)."</docs>\n";
		}
		if($this->ttl!=""){
			$feed.= "        <ttl>".htmlspecialchars($this->ttl)."</ttl>\n";
		}
		if($this->rating!=""){
			$feed.= "        <rating>".FeedCreator::iTrunc(htmlspecialchars($this->rating),500)."</rating>\n";
		}
		if($this->skipHours!=""){
			$feed.= "        <skipHours>".htmlspecialchars($this->skipHours)."</skipHours>\n";
		}
		if($this->skipDays!=""){
			$feed.= "        <skipDays>".htmlspecialchars($this->skipDays)."</skipDays>\n";
		}
		$feed.= $this->_createAdditionalElements($this->additionalElements,"    ");

		for ($i=0;$i<count($this->items);$i++){
			$feed.= "        <item>\n";
			$feed.= "            <title>".FeedCreator::iTrunc(htmlspecialchars(strip_tags($this->items[$i]->title)),100)."</title>\n";
			$feed.= "            <link>".htmlspecialchars($this->items[$i]->link)."</link>\n";
			$feed.= "            <description>".$this->items[$i]->getDescription()."</description>\n";

			if($this->items[$i]->author!=""){
				$feed.= "            <author>".htmlspecialchars($this->items[$i]->author)."</author>\n";
			}
			/*
			 // on hold
			 if($this->items[$i]->source!=""){
			 $feed.= "            <source>".htmlspecialchars($this->items[$i]->source)."</source>\n";
			 }
			 */
			if($this->items[$i]->category!=""){
				$feed.= "            <category>".htmlspecialchars($this->items[$i]->category)."</category>\n";
			}
			if($this->items[$i]->comments!=""){
				$feed.= "            <comments>".htmlspecialchars($this->items[$i]->comments)."</comments>\n";
			}
			if($this->items[$i]->date!=""){
				$itemDate=new FeedDate($this->items[$i]->date);
				$feed.= "            <pubDate>".htmlspecialchars($itemDate->rfc822())."</pubDate>\n";
			}
			if($this->items[$i]->guid!=""){
				$feed.= "            <guid>".htmlspecialchars($this->items[$i]->guid)."</guid>\n";
			}
			$feed.= $this->_createAdditionalElements($this->items[$i]->additionalElements,"        ");
			$feed.= "        </item>\n";
		}
		$feed.= "    </channel>\n";
		$feed.= "</rss>\n";
		return $feed;
	}
}

class RSSCreator20 extends RSSCreator091{

	function RSSCreator20(){
		parent::_setRSSVersion("2.0");
	}

}

使用示例：

<?php
header('Content-Type:text/html; charset=utf-8');
$db=mysql_connect('127.0.0.1','root','123456');
mysql_query("set names utf8");
mysql_select_db('dbname',$db);
$brs=mysql_query('select * from article order by add_time desc limit 0,10',$db);
$rss=new UniversalFeedCreator();
$rss->title="页面标题";
$rss->link="网址http://";
$rss->description="rss标题";
while($rowbrs=mysql_fetch_array($brs)){
	$item=new FeedItem();
	$item->title =$rowbrs['subject'];
	$item->link='http://php.hhsy.cc/';
	$item->description =$rowbrs['description'];
	$rss->addItem($item);
}
mysql_close($db);
$rss->saveFeed("RSS2.0","rss.xml");