How to read the link function of a certain site in PHP_PHP tutorial

Principle: Read the source file of a site, then use regular expressions to analyze its source code, and get all the links
))$url = "http://www.csdn.net/expert/";//Set url
　$site=substr($url,0,strpos($url,"/",8)); //Site
　$base=substr($url,0,strrpos($url,"/")+1);//The directory where the file is located
　
　$fp = fopen($url, "r " );//Open url
while(!feof($fp))$contents.=fread($fp,1024);//

$pattern="|href=["]? ([^ "]+)[" ]|U";
preg_match_all($pattern,$contents, $regArr, PREG_SET_ORDER);//Match all href=
for($i=0;$i< count($regArr);$i++){//Traverse all matches
　if(!eregi("://",$regArr[$i][1]))//Whether it is a relative path, that is, whether it is still There are://
　if(substr($regArr[$i][1],0,1)=="/")//Whether it is the root directory of the site
　echo "link".($i +1).":".$site.$regArr[$i][1]."
";//Root directory
　else
　echo "link".($i+ 1).":".$base.$regArr[$i][1]."
";//Current directory
　else
　echo "link".($i+1 ).":".$regArr[$i][1]."
";//Relative path
　}
　fclose($fp);
　?>

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