posix_access() checks the user's permission of a file.
当安全模式被激活时，PHP 将检查被操作的文件或者目录是否与正在执行的脚本有相同的 UID（所有者）。
The name of the file to be tested.
A mask consisting of one or more of POSIX_F_OK,
POSIX_R_OK, POSIX_W_OK and
POSIX_X_OK. Defaults to
POSIX_F_OK.
POSIX_R_OK, POSIX_W_OK and
POSIX_X_OK request checking whether the file
exists and has read, write and execute permissions, respectively.
POSIX_F_OK just requests checking for the
existence of the file.
This example will check if the $file is readable and writable, otherwise will print an error message.
<?php
$file = 'some_file';
if (posix_access($file, POSIX_R_OK | POSIX_W_OK)) {
echo 'The file is readable and writable!';
} else {
$error = posix_get_last_error();
echo "Error $error: " . posix_strerror($error);
}
?>