what about $exists or $isfile
could have done that, I'm sure I had a reason not to do so.

and you can replace == $null by adding "!" before the identifer
Not my style, sorry.

and remove the "()" around the condition it will make the code slower
I really doubt it matters much, and if it does, then stop using the dusty old 486 in your mums basement as your PC (:

I prefer my code to be readable over "fast", especially when there's no real significant speed gain... 1ms more or less is not going to kill you with something trivial as this.