Windows 10: Case sensitive file and folder names

By default Windows processes treat the file system as case-insensitive. As such they do not differentiate between files or folders based on case. For example, filenames FILE.txt and file.txt are viewed as the same file, even where their content and all other information is different.

In normal operation this does not cause an issue, however problems may occur where files or folders came from a file system that supports case sensitivity such as Linux or UNIX, or where the computer is using the Windows Subsystem for Linux (a compatibility layer for natively running Linux binary executables on Windows).

To make it easier to deal with case sensitivity when handling this type of file or folder. The Windows 10 April 2018 Update (version 1803) introduced a new flag, configurable on a per-directory basis. When enabled, all Windows processes will respect the case sensitivity of the folder and its files, so they view FILE.txt and file.txt as different files.

This setting only applies to the selected folders and associated files. Not the entire file system. Additionally, the settings is not inherited by any sub-folders created in a case sensitive directory.
This can affect user entered file and folder location in some native Windows processes, including Managed Antivirus Exclusions. If the location does not precisely match the case file and folder case. The Windows process will be unable to query these locations.

Managed Antivirus Exclusion Case Sensitive File Location Example

The following example uses the eicar anti-malware test file:

Case Sensitive File Location
%LOCALAPPDATA%\AppData\LOCAL\eicar.com
Managed Antivirus Exclusion	Behavior
%LOCALAPPDATA%\AppData\LOCAL\eicar.com	Test file ignored (excluded)
%LOCALAPPDATA%\appdata\local\eicar.com	Test file quarantined

Check Folder Case Sensitivity

To check whether a folder is case sensitive, run the following from a command prompt:

fsutil.exe file queryCaseSensitiveInfo <path>

For examplecommand and response:

What do you want to do?

• Read about Exclusion management and notes
• Review the Exceptions Common System Variables
• Investigate the Microsoft Developer Blog on Per-directory case sensitivity and WSL

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