FileNames[]
FileNames
[form]FileNames
[{$form_1$, $form_2$, ...}]FileNames
[{$form_1$, $form_2$, ...},{$dir_1$, $dir_2$, ...}]FileNames
[{$form_1$, $form_2$, ...},{$dir_1$, $dir_2$, ...}]FileNames
[{forms, dirs, n]SetDirectory[$InstallationDirectory <> "/autoload"];
FileNames["*.m", "formats"]//Length
FileNames["*.m", "formats", 3]//Length
FileNames["*.m", "formats", Infinity]//Length