Renaming directories with invalid names

Somehow, a client managed to create several directories with names that ended with a period. However, File Explorer and other tools (i.e., backup) are unable to access the folder contents, getting an error that usually is interpreted as “The system cannot find the file specified.”

According to KB2829981, the Win32_API is supposed to remove trailing space and period characters. KB320081 has some helpful suggestions, and also indicates that some techniques allow programs to bypass the filename validation checks, and some POSIX tools are not subject to these checks.

I found that I was able to delete these problem folders by using rmdir /q /s “\\?\J:\path\to\bad\folder.” But I wanted to rename the folders in order to preserve any content. After flailing about for a while, including attempts to modify the folders using a MacOS Client and a third-party SSH service on the host, I was prodded by my colleague Greg to look at Robocopy.

In the end, my solution was this:

  1. I enabled 8dot3 file name creation on a separate recovery volume (I didn’t want to do so on the multi-terabyte source volume)
  2. Using robocopy, I duplicated the parent folder containing the invalid folder names to the recovery volume, resulting in the creation of 8dot3 names for all the folders
  3. I listed the 8dot3 names of the problem folders with dir /x
  4. The rename command with the short name as a source and a valid new name

This fixed the folders, and let me access their contents. I then deleted the invalid folders from the source and copied the renamed folders into place.

It seems like a simple process, but I managed to waste most of a morning figuring this out. Hopefully, this may save someone else some time.

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