An example of how to use PHP to check whether a website is down

<?php
function Networkcheck($url){
  $agent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0";
  //curl_init-初始化一个curl会话
  $ch=curl_init();
  //curl_setopt — 为一个curl设置会话参数
  curl_setopt($ch, CURLOPT_URL,$url );
  curl_setopt($ch, CURLOPT_USERAGENT, $agent);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($ch,CURLOPT_VERBOSE,false);
  curl_setopt($ch, CURLOPT_TIMEOUT, 5);
  curl_setopt($ch,CURLOPT_SSL_VERIFYPEER, FALSE);
  curl_setopt($ch,CURLOPT_SSLVERSION,3);
  curl_setopt($ch,CURLOPT_SSL_VERIFYHOST, FALSE);
  //curl_exec —执行一个curl会话
  $page=curl_exec($ch);
  //curl_getinfo — 获取一个curl连接资源句柄的信息
  $httpcode = curl_getinfo($ch, CURLINFO_HTTP_CODE);
  //curl_close()函数的作用是关闭一个curl会话，唯一的参数是curl_init()函数返回的句柄。
  curl_close($ch);
  if($httpcode>=200 && $httpcode<300)
    return true;
  else
    return false;
}
//函数参数为要检查的网站的网址路径
if(Networkcheck("https://www.baidu.com"))
  echo "Website OK";
else
  echo "Website DOWN";
?>