is_file() 函数检查指定的文件名是否是正常的文件。
is_file — Tells whether the filename is a regular file
用法

bool is_file ( string $filename ) $file 为必选参数
如果文件存在且为正常的文件则返回 TRUE。

来看一个测试is_file经典实例

<?php 
var_dump(is_file('a_file.txt')) . "n"; 
var_dump(is_file('/usr/bin/')) . "n"; 
?> 

上例将输出：
bool(true)
bool(false)
用法二

<?php 
function isfile($file){ 
return preg_match('/^[^.^:^?^-][^:^?]*.(?i)' . getexts() . '$/',$file); 
//first character cannot be . : ? - subsequent characters can't be a : ? 
//then a . character and must end with one of your extentions 
//getexts() can be replaced with your extentions pattern 
} 
function getexts(){ 
//list acceptable file extensions here 
return '(app|avi|doc|docx|exe|ico|mid|midi|mov|mp3| 
mpg|mpeg|pdf|psd|qt|ra|ram|rm|rtf|txt|wav|word|xls)'; 
} 
echo isfile('/Users/YourUserName/Sites/index.html'); 
?> 

实例三

<?php 
function deletefolder($path) 
{ 
if ($handle=opendir($path)) 
{ 
while (false!==($file=readdir($handle))) 
{ 
if ($file<>"." AND $file<>"..") 
{ 
if (is_file($path.'/'.$file)) 
{ 
@unlink($path.'/'.$file); 
} 
if (is_dir($path.'/'.$file)) 
{ 
deletefolder($path.'/'.$file); 
@rmdir($path.'/'.$file); 
} 
} 
} 
} 
} 
?> 

此函数删除所有事情，定义的文件夹