Is there any way to globally hide every single file extension in OS X? I've seen the option in the Get Info menu to hide the selected file's extension, but I'd like to never see a file extension unless I chose to.
I use Hazel with an applescript to keep my filename extensions hidden. Hazel is just a way to make sure that anytime I create a new file, the applescript gets run on it. The applescript is pretty easy -- you can see all three lines of it in the screenshot below. I also like to set the color labels by file type, thus the selection of only PDFs and the red color labels. You can skip both of those if you like.
Just to be clear, you don't need to use Hazel. You could use folder actions or an automator workflow to initiate the applescript on the files you want to change.
The only correct answer is that you should not be doing what you are trying to do.
Hidden file extensions is a serious security hole. If you allow file extensions to be hidden, someone can create an application and name it:
and on your machine, you will see a file named:
possibly even with a PDF icon. Your first thought will not be, "Why is the extension showing?" but rather, "Oh, that's just a PDF file. It's safe to open it." And that's when your machine becomes a zombie in a botnet.
You should always leave the "Show all filename extensions" checkbox checked. It's really the only way to be completely safe from those sorts of trojans.