How to use php keep only specific file and remove others in directory?

Question

How to use php keep only specific file and remove others in directory?

example:
1/1.png, 1/2.jpeg, 1/5.png ...

the file number, and file type is random like x.png or x.jpeg, but I have a string 2.jpeg the file need to keep.

any suggestion how to do this??

Thanks for reply, now I coding like below but the unlink function seems not work delete anything.. do I need change some setting? I'm using Mamp

UPDATE

// explode string <img src="u_img_p/5/x.png">
$content_p_img_arr = explode('u_img_p/', $content_p_img);
$content_p_img_arr_1 = explode('"', $content_p_img_arr[1]);    // get 5/2.png">
$content_p_img_arr_2 = explode('/', $content_p_img_arr_1[0]);    // get 5/2.png
print $content_p_img_arr_2[1];    // get 2.png   < the file need to keep

$dir = "u_img_p/".$id;  
if ($opendir = opendir($dir)){
    print $dir;
    while(($file = readdir($opendir))!= FALSE )
        if($file!="." && $file!= ".." && $file!= $content_p_img_arr_2[1]){
            unlink($file);
            print "unlink";
            print $file;
        }
    }
} 

I change the code unlink path to folder, then it works!!

 unlink("u_img_p/".$id.'/'.$file);  

Answer 1

 $dir = "your_folder_path";  
 if ($opendir = opendir($dir)){
    //read directory
     while(($file = readdir($opendir))!= FALSE ){
      if($file!="." && $file!= ".." && $file!= "2.jpg"){
       unlink($file);
      }
     }
   }