I originally have a file called config.yml. When I go into Finder and change its name to config.yml.old, it appears to have changed the extension. However, opening the file in TextWrangler reveals that Mac has just appended a "hidden" .yml at the end, causing the filename to be config.yml.old.yml.

Right now, the only way I can append an extension is by going to Terminal and running mv path/to/config.yml path/to/config.yml.old. Is there actually a way to use the GUI to do this?

  1. Go to Finder
  2. open Finder Preferences
  3. Uncheck "Show warning before changing an extension"

Optionally, check "Show all filename extensions" to verify that Mac did not automatically append extensions when you add your own.

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