这是一个记录用户踪迹的片段

<?php
if($_GET[mode]) {
  $mode = $_GET[mode];
  $url = $_GET[url];
  $ip = $_SERVER[REMOTE_ADDR];
  $fp = fopen("msg.txt","a+");
  fputs($fp,"$ip ".date("Y-m-d H:i:s")." $mode $url\n");
  fclose($fp);
  exit;
}
?>
<body onunLoad="msg('off')" onLoad="msg('on')">
<span id="view" style="visibility:hidden"></span>
</body>
<script>
function msg(v) {
  view.innerHTML = '<iframe src="msg.php?mode='+v+'&url='+location.href+'"></iframe>';
}
</script>