$url = ‘http://www.sina.com.cn/abc/de/fg.php?id=1‘;
$url = parse_url($url,PHP_URL_PATH);  
echo pathinfo($url,PATHINFO_EXTENSION).PHP_EOL;  //1

$url = explode(‘.‘,$url);//2
echo end($url).PHP_EOL;

echo ltrim(strrchr($url,‘.‘),‘.‘).PHP_EOL; //3

echo substr(strrchr($url,‘.‘),1).PHP_EOL; //4

echo substr($url,strrpos($url,‘.‘)+1).PHP_EOL; //5