Regular expression for valid filename

Question

I already gone through some question in StackOverflow regarding this but nothing helped much in my case.

I want to restrict the user to provide a filename that shoul

Answer 1

I've just created this. It prevents two dots and dot at end and beginning. It doesn't allow any two dots though.

^([a-zA-Z0-9_]+)\.(?!\.)([a-zA-Z0-9]{1,5})(?