PHP的文件操作函数几乎都能用来发送http请求：

$html = file_get_contents('http://ww.google.com');
var_dump($html);

有些网站会对请求头信息进行检测，这时候就需要用到curl了（php.ini中要启用curl扩展），贴一个我一直用的函数：

function fetch_page($site,$url,$params=false)
{
    $ch = curl_init();
    $cookieFile = $site . '_cookiejar.txt';
    curl_setopt($ch, CURLOPT_COOKIEJAR, $cookieFile);
    curl_setopt($ch, CURLOPT_COOKIEFILE,$cookieFile);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($ch,   CURLOPT_SSL_VERIFYPEER,   FALSE);
    curl_setopt($ch, CURLOPT_HTTPGET, true);
    curl_setopt($ch, CURLOPT_TIMEOUT, 4);
    if($params)
        curl_setopt($ch, CURLOPT_POSTFIELDS, $params);
    curl_setopt($ch,CURLOPT_USERAGENT,'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3');
    curl_setopt($ch, CURLOPT_URL,$url);

    $result = curl_exec($ch);
    //file_put_contents('jobs.html',$result);
    return $result;
}

调用示例：

$html = fetch_page('google','http://googlel.com','key=value');
var_dump($html);

如果请求类型是https,则只能用curl了，前者会报（至少默认情况下）：

PHP Warning: file_get_contents(): Unable to find the wrapper "https" - did you forget to enable it when you configured PHP?