File Extensions Missing

You may be able to use this procedure:

1. Select an individual file.
2. Press COMMAND-I to open the Get Info window.
3. In Open With section select the default application you want associated with that file.
4. Click the Change All button.

This will associate that file and similar files to the selected application. You may not need to append a file extension.

However, if this doesn't work then get a utility such as BatchRename'em 1.2 - CNet Downloads or MacUpdate - that you can use to rename files by simply adding an extension to all selected files. That way you could change hundreds of files at once.

Here's the thing. Normally, files are created with extensions but the extensions are hidden. If you select a file of a particular type you can use Get Info to change the display from hidden to visible in order to see the file extension. Get Info will actually display the file with its extension. But in the case you describe it sounds like all the file extensions were somehow removed. The result being that OS X treats them as "unknown" which defaults to the Unix executable type. These files now have apparently become associated with the Terminal. There is no simple way to determine what type of file each is nor the application that originally created it. Since the extensions were apparently removed there is no way to recover them.

Do you have a backup?