how cat get the file extension?

[eluser]tnathos[/eluser]
hi, how i can get the file extension before upload the file? i need know for put the correct path..

img_principal is the input type file in the view...

Code:

$config['file_1']['upload_path']     = './uploads/logos/';
            $config['file_1']['allowed_types']  = 'gif|jpg|png';
            $config['file_1']['encrypt_name']     = true;
        
        !!!!!! here !!!! how can? if(['img_principal']['file_ext']=='swf' ){
        
            $config['file_2']['upload_path']     = './uploads/medios/swf';
            $config['file_2']['allowed_types']  = 'swf|fla';
            $config['file_2']['encrypt_name']     = true;
        
        }else{
        
            $config['file_2']['upload_path']     = './uploads/medios/img';
            $config['file_2']['allowed_types']  = 'gif|jpg|png';
            $config['file_2']['encrypt_name']     = true;
        }