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Why Can’t I Rename Files to Upper or Lowercase on USB Drives

Here’s a user query where they’re unable to change the file name extension to lowercase from uppercase (or the other way) on external drives. For instance, the command-line to bulk change the extension (ren *.WAV  *.wav) may work on the system drive but not on an external drive.


My audio devices produce thousands of .WAV files — e.g., V001_20220621_023000.WAV. To analyze them, I use an R-package, but the scripts use”.wav“, so the commands do not work with my files. I tried to rename them with a couple of files in a test folder on the C: drive with “ren *.WAV *.wav“. This worked perfectly. BUT my files are stored on an external drive E:

So I set the path in cmd to the folder with my files (also a test folder, to be sure) and used the same command as before, but nothing happened. I searched through some forums for a solution, but could not find one. The files have no limitations for writing or reading. I run the cmd.exe as administrator. The external drive can be used by all users on the computer. There are no spaces in the file names. I’ve also tried renaming with Microsoft PowerToys PowerRename. That didn’t help.


Your external drive(s) may be formatted as FAT32. On FAT32 drives, changing the file names to lowercase can be done only if you make some other modification to the filename — e.g., change the file name or its extension.

In other words, if the rename operation is only for changing the capitalization/case of a file, then FAT32 doesn’t support it. It works if the rename operation is more than just changing a lowercase to a capital or vice versa.

Rename files or folders in two passes

To work around this, you can rename a file/folder or a set of files in two passes, as follows.

Example 1: To change a name/extension to lowercase:

If it’s a single file, you can simply use File Explorer to rename the file twice/2 passes. If using Command Prompt, try this:

Note: Be sure to use a unique file name for renaming. If a file exists with the same name (e.g., Media.txt.2022) in that folder, there will be a conflict.

Example 2: To bulk change extension to lowercase (.WAV to .wav):

I hope that helps.

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