curl命令示例：
curl -I -m 10 -o /dev/null -s -w %{http_code} http://test.com
curl爬取过程中，会返回一个http_code。
相关解释：
$http_code["0"]="Unable to access";
$http_code["100"]="continue";
$http_code["101"]="Switching Protocols";
$http_code["200"]=”OK”;
$http_code["201"]=”Created”;
$http_code["202"]=”Accepted”;
$http_code["203"]=”Non-Authoritative Information”;
$http_code["204"]=”No Content”;
$http_code["205"]=”Reset Content”;
$http_code["206"]=”Partial Content”;
$http_code["300"]=”Multiple Choices”;
$http_code["301"]=”Moved Permanently”;
$http_code["302"]=”Found”;
$http_code["303"]=”See Other”;
$http_code["304"]=”Not Modified”;
$http_code["305"]=”Use Proxy”;
$http_code["306"]=”(Unused)”;
$http_code["307"]=”Temporary Redirect”;
$http_code["400"]=”Bad Request”;
$http_code["401"]=”Unauthorized”;
$http_code["402"]=”Payment required”;
$http_code["403"]=”Forbidden”;
$http_code["404"]=”Not Found”;
$http_code["405"]=”Method Not Allowed”;
$http_code["406"]=”Not Acceptable”;
$http_code["407"]=”Proxy Authentication Required”;
$http_code["408"]=”Request Timeout”;
$http_code["409"]=”Conflict”;
$http_code["410"]=”Gone”;
$http_code["411"]=”Length Required”;
$http_code["412"]=”Precondition Failed”;
$http_code["413"]=”Request Entity Too Large”;
$http_code["414"]=”Request-URI Too Long”;
$http_code["415"]=”Unsupported Media Type”;
$http_code["416"]=”Requested Range Not Satisfiable”;
$http_code["417"]=”Expectation Failed”;
$http_code["500"]=”Internal Server Error”;
$http_code["501"]=”Not Implemented”;
$http_code["502"]=”Bad Gateway”;
$http_code["503"]=”Service Unavailable”;
$http_code["504"]=”Gateway Timeout”;
$http_code["505"]=”HTTP Version Not Supported”;