Two examples of php global variable $_SERVER

<?php
$address = $_SERVER['REMOTE_ADDR'];
$referer = $_SERVER['HTTP_REFERER'];
$browser = $_SERVER['HTTP_USER_AGENT'];

$file = fopen("log.html",  "a");  

$time = date("H:i dS F");
fwrite( $file, "<b>时 间:</b> $time<br>" );

if( $address != null)
{
  fwrite( $file, "<b>IP 地址:</b> $address <br>");
}  

if( $referer != null)
{
  fwrite( $file, "<b>来 源:</b> $referer<br>");  
}

fwrite( $file, "<b>浏览器:</b> $browser<br/><hr>");  
fclose($file);
?>

<?php if ($_SERVER['REQUEST_METHOD'] == 'GET') { ?>
<form action="<?php echo $_SERVER['SCRIPT_NAME'] ?>" method="post">
您的姓名?
<input type="text" name="first_name" />
<input type="submit" value="Say Hello" />
</form>
<?php } else {
    echo '您好, ' . $_POST['first_name'] . '!';
}
?>