Validate if the field of a form is empty

Hi, I need to validate a field that work with Multifile plugin of Jquery, I want to check if the field is empty with php. [code] <input name="archivo[]" class="multi" type="file" accept="gif|jpg|png"/> <input name="button" type="submit" value="Submit"> [code] I've tried different ways but it does not work: for example: $field = $_FILES["archivo"]["name"]; $field = $_FILES["archivo[]"]["name"]; i dont know how to validate it, any help would be appreciated. Thanks,