Filesystem and Directory Functions

[chinmay.sahoo]

Most of these functions will be quite familiar to Unix users, as they closely replicate common system commands .

Many of the functions in this section are dangerous. Because they duplicate functions that can and should be performed from the local system, they can be a crаcker’s bonanza without providing much value to legitimate users. Strongly consider disabling them using PHP’s disable_functions directive (as discussed in the preceding section on file writing)!

The one piece of good news is that some of these functions will only work if the PHP process is running as the superuser. Because this is not the default case in the Web browser, presumably these functions are intended to be used by the scripting version of PHP, and only trusted users who know what they’re doing are even in a position to shoot themselves in the foot this way. Of course, if you are foolish enough to run your Web server as root, you are doubly screwed.

[TomClarke]

Here are two great articles on this topic. In this http://www.php.net/manual/fa/ref.filesystem.php you will find information about filesystem  functions and in this one http://ua2.php.net/manual/fa/ref.dir.php you can read information about directory functions!
Good luck!