文件权限是指可以对系统中的特定文件执行的操作，例如，读取，写入或执行文件。下面本篇文章就来给大家介绍使用PHP如何进行文件权限的检查和更改，希望对大家有所帮助。
PHP会在幕后自动授予适当的权限。例如，如果创建一个新文件进行编写，PHP会自动授予其读写权限。此外，PHP还提供了一些用于检查和更改文件权限的有用功能。
PHP如何检查文件权限？
PHP为我们提供了三个函数，用来检查文件权限：
is_readable()函数：用于检查是否有读取权限，如果允许读取文件，则返回true，否则返回false。
is_writable()函数：用于检查是否有写入权限，如果允许写入文件，则返回true，否则返回false。
is_executable()函数：用于检查是否有执行权限，如果允许执行文件，则返回true，否则返回false。
代码示例：
<?php
header(“content-type:text/html;charset=utf-8”);
$fn = ‘demo/test.txt’;
$ msg = is_readable($fn) ? $msg = ‘文件是可读的’
: $msg = ‘文件不可读’;
echo $msg . ‘<br/>’;
$msg = is_writable($fn) ? $msg = ‘文件是可写的’
: $msg = ‘文件不可写’;
echo $msg . ‘<br/>’;
$msg = is_executable($fn) ? $msg = ‘文件是可执行的’
: $msg = ‘文件不可执行’;
echo $msg . ‘<br/>’;
?>
输出：
除了这些函数之外，php还提供fileperms()函数，该函数返回一个整数，表示对特定文件设置的权限。
<?php
$fn = ‘demo/test.txt’;
$ fp = fileperms($fn);
echo substr(sprintf(‘%o’, $fp), -4); //0666
?>
输出：
0666
PHP如何更改文件权限？
要更改文件权限或模式，需要使用 chmod ()函数。首先，需要传递要设置权限的文件名；然后，需要指定所需的权限。如果成功设置了权限，chmod()函数将返回true，否则返回false。
文件权限由包含三位数字的八进制数表示：
● 第一个数字指定文件的所有者可以对文件执行的操作。
● 第二个数字指定文件的所有者组可以对文件执行的操作。
● 第三个数字指定每个人可以对文件执行的操作。
下表说明了表示特定用户（用户，用户组或所有人）的访问权限的每个数字的值：
● 0：不能读，写或执行
● 1：只能执行
● 2：只能写
● 3：可以写和执行
● 4：只能读
● 5：可以阅读和执行
● 6：可以读写
● 7：可以读，写和执行
例如，要设置创建者或所有者、以及其他人只能读取该文件，我们使用以下代码：
<?php
$fn = ‘demo/test.txt’;
//更改权限
chmod($fn, 0444);
//读取权限
$msg = is_readable($fn) ? $msg = ‘文件是可读的’
: $msg = ‘文件不可读’;
echo $msg . ‘<br/>’;
$msg = is_writable($fn) ? $msg = ‘文件是可写的’
: $msg = ‘文件不可写’;
echo $msg . ‘<br/>’;
$msg = is_executable($fn) ? $msg = ‘文件是可执行的’
: $msg = ‘文件不可执行’;
echo $msg . ‘<br/>’;
?>
输出：
注意：我们在644之前放置0，要求PHP将其解释为八进制数。
相关视频教程推荐：《PHP教程》
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