PHP：is_dir（）用于诸如“./folder”之类的文件夹返回false，除非我将它们指定为“../folder”

Question

The hierarchy of my site is like this:

/
/webroot/
/webroot/index.php
/webroot/images/foo.jpg

I do not have write permissions for /, but I do for anything within /webroot.
Now say within index.php I have any of these commands:

var_dump(is_dir('./images/frontpage'));
var_dump(is_dir('images/frontpage'));
var_dump(is_dir('/webroot/images/frontpage'));
var_dump(is_dir('.\images\frontpage'));

They will all return false. But if within webroot\index.php I have...

    var_dump(is_dir('../images'));

...they return true. Am I missing something obvious? Is it supposed to work this way? I don't understand this.

BUT: If I have something like this:

/
/webroot/
/webroot/index.php
/webroot/images/foo.jpg
/webroot/subfolder/index.php

Then var_dump(is_dir('../images')); will return true both in index.php and in subfolder/index.php

Answer 1

Both will return true if you are calling them from /webroot/subfolder/.

.. and . depends on your current working directory. Calling /webroot/index.php from /webroot/subfolder/some.php will make /webroot/subfolder/ the current working directory. Hence '../images' will always be a directory and it'll return true.