Changing the File Name, the Extension or Both

Most actions have a Change: popup menu below their settings. It decides which part of the name the action works on:

• only the file name leaves the extension alone. This is the default for most actions
• only the file extension changes the characters after the dot, e.g. jpeg in photo.jpeg
• only the file extension (including separator) includes the dot, e.g. .jpeg
• both the file name and the extension treats the whole name as one piece of text

Examples

• Change .jpeg to .jpg: choose the Replace text action, replace jpeg with jpg and set Change: to only the file extension, so that holiday.jpeg → holiday.jpg
• Make all extensions lowercase: choose Convert to lowercase and set Change: to only the file extension, so that Scan.PDF → Scan.pdf
• Add an extension to files that have none: choose Add text to end, type .txt and set Change: to both the file name and the extension, so that notes → notes.txt

Things to watch

macOS uses the extension to decide which application opens a file. If files no longer open after a rename, the extension was probably changed or removed; adding the original extension back fixes it. The Finder also hides extensions in some cases, so a name that looks like holiday may really be holiday.jpg. Select the file in the Finder and choose File › Get Info to see the full name under Name & Extension.

The Show Invisible Characters option in View › Preview makes spaces at the end of a name visible, which is another common reason why an extension does not look right.