一 代码
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>应用正则表达中的点字符（.）</title>
<style type="text/css">
<!--
body {
margin-left: 0px;
margin-top: 0px;
margin-right: 0px;
margin-bottom: 0px;
}
-->
</style></head>
<body>
<?php
$checkip="/^(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9])(\.)(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])(\.)(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])(\.)(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9])$/";
if($_POST[check_ip]!="" and $_POST[Submit]=="提交"){
if(preg_match($checkip,$_POST[check_ip],$counts)){
echo "<script>alert('IP地址格式正确!');window.location.href='index.php';</script>";
}else{
echo "<script>alert('IP地址格式不正确!');window.location.href='index.php';</script>";
}
}
?>
<table width="851" height="483" border="0" align="center" cellpadding="0" cellspacing="0" background="images/bg.jpg">
<tr>
<td height="119" colspan="3"> </td>
</tr><form id="form1" name="form1" method="post" action="index.php">
<tr>
<td width="336" height="264"> </td>
<td width="260" align="center" valign="top">IP地址：
<input type="text" name="check_ip" /></td>
<td width="255" valign="top"><input type="submit" name="Submit" value="提交" /></td>
</tr></form>
<tr>
<td height="100"> </td>
<td> </td>
<td> </td>
</tr>
</table>
</body>
</html>
二 运行结果
输入：56.06.45.33
输出：IP地址格式不正确