how to get the extention of a file in a custom laravel rules using the value paramter code example

Example 1: laravel return validation errors

@if($errors->any())
   @foreach ($errors->all() as $error)
      <div>{{ $error }}</div>
  @endforeach
@endif

Example 2: laravel validation

/**
 * Bootstrap any application services.
 *
 * @return void
 */
public function boot()
{
    Validator::extend(...);

    Validator::replacer('foo', function ($message, $attribute, $rule, $parameters) {
        return str_replace(...);
    });
}