OS X Mountain Lion: Show and hide filename extensions
A filename extension consists of a dot (.) followed by several letters that identify the type of file (for example, .txt or .jpg). The extension can determine which app opens the file.
Filename extensions are usually hidden in OS X, but if you find them useful, you can show them. In some apps you can choose to show a document’s filename extension when you save the document.
If filenames are showing and you decide to hide them, OS X is still able to open the files with the proper apps.
For one file
- Select a file and choose File > Get Info or press Command (⌘)–I.
- Click the triangle next to Name & Extension to expand the section and see the filename extension for the file.
- To show or hide the filename extension, select or deselect “Hide extension.”
For all files
- Choose Finder > Preferences, and then click Advanced.
- Select or deselect “Show all filename extensions.”
Some filename extensions can’t be hidden. For example, images imported from a digital camera may continue to show the .jpg extension even after you deselect “Show all filename extensions.”