Validate That A String Passing Through Always = "*.extension"

I wish I had never let go of my old pearl days, but those days are behind us Now, for the life of me, I can't remember how to write the regex I need I keep getting "TOO MUCH" validation!

the expression i have so far is: "(.*?).(jpg|jpeg|gif|doc|pdf)$"

but i know tis a little off for what I need What i need is to validate that a string passing through always = "*.extension"For instance, somehow, some strange way, user passes string as "bob.pdf"I want to convert the "bob.pdf" to "*.pdf"Or, say they just pass "jpg", then it needs to become "*.jpg"

Of course there is a billion other ways to do this, but none I can think of that would be less proc intensive than using regex I just can't remember the danged line I NEED!the ultimate goal in end of course is to set up:

[Code]...