c# EnumerateFiles wildcard returning non matches?

Question

As a simplified example I am executing the following

IEnumerable<string> files = Directory.EnumerateFiles(path, @"2010*.xml", 
    SearchOption.TopDirectoryOnly).ToList();

In my results set I am getting a few files which do no match the file pattern. According to msdn searchPattern wildcard is "Zero or more characters" and not a reg ex. An example is that I am getting a file name back as "2004_someothername.xml".

For information there are in excess of 25,000 files in the folder.

Does anyone have any idea what is going on?

Answer 1

This is due to how Windows does wildcard matching - it includes the encoded 8.3 filenames in its wildcard search, resulting in some surprising matches!

A way to get around this bug is to retest all file results that come back through the OS wildcard match and test with a manual comparison of the wildcard to each (long) file name. Another way is to turn off 8.3 filenames altogether via the registry. I have been burned by this on numerous occasions, including having important (non-matching) files get deleted via a wildcard based del command from the command prompt.

To summarize, be very careful, especially if you have many files in a directory on making any critical production decisions or taking any actions based on an OS file/wildcard match, without a secondary verification of results.

Here is an explanation of this bizarre behavior.

Another explanation from O'Reilly's site.