You may retrieve all needed file path data using PHP's built-in function pathinfo. You don't need to create your own functions or use regular expressions to get this info. It was already been created for this purpose

gistfile1.aw

    <?php
    /* Source: http://www.apphp.com/index.php?snippet=php-get-remote-ip-address */
    // pathinfo() constants parameter list
    // PATHINFO_DIRNAME  => directory name
    // PATHINFO_BASENAME => name of file (w/out extension)
    // PATHINFO_EXTENSION => file extension
    // PATHINFO_FILENAME   => file name w/ extension
     
    $path = '/images/thumbs/my_avatar.gif';
     
    //outputs '/images/thumbs/'
    echo pathinfo($path, PATHINFO_DIRNAME);
     
    //outputs 'my_avatar'
    echo pathinfo($path, PATHINFO_BASENAME);
     
    //outputs 'my_avatar.gif'
    echo pathinfo($path, PATHINFO_FILENAME);
     
    //outputs 'gif'
    echo pathinfo($path, PATHINFO_EXTENSION);
    ?>