怎么利用PHP去ping一个地址

$hname = getenv("HTTP_HOST");

echo "<b>Your IP is:</b> <i>$ip</i><br>"

."<b>Trying to ping:</b> <i>$server</i><br>"

."<b>Using server:</b> <i>$hname</i>";

echo "<HR noshade size=1<br>";

echo "<b>STATS:</b><br><br>";

$command = "ping -c4 $server";

exec($command, $result, $rval);

if(count($result) <= 0) {

echo "<font color=red>没有响应</font><br>";

echo "<HR noshade size=1>";

exit;

}

for ($i = 0; $i < count($result); $i++) {

echo "<font color=red>$result[$i]</font><br>";

}

echo "<HR noshade size=1>";

#include("powered.txt");

}

?>