Weird functionality in .NET's Directory.GetFiles() when search pattern contains 3 chars for extension

Question

I recently bumped into a weird functionality from Microsoft:

Let's assume our folder c:\tmp123 contains 3 files -
1.txt
2.txtx
3.txtxt

a) Invocation of Directory.GetFiles(@"C:\tmp123", "*.txt") yields in 3 returned items.
b) Invocation of Directory.GetFiles(@"C:\tmp123", "*.txtx") yields in 1 returned items.

According to Microsoft this is the expected behavior (see Note in MSDN).

My questions are:

1. Why did Microsoft decide to have such a strange functionality?

2. How can I overcome this problem?
   i.e. how do I have a Search Pattern that would return *.txt extension only and not return *.txtx, *.txtstarngefunctionality, etc.?

Answer 1

The reason for this is backwards compatibility.

Windows was initially built as a graphical interface on top of MSDOS which only had files with 8 characters for the name and a maximum of 3 for the extension. Extentions to the MSDOS file systems allowed Windows to have longer file names and extensions but these would still show up as 8.3 file names in MSDOS.

Since the command prompt on Windows is an evolution of the old command interpreter in MSDOS this means some "anachronistic" behaviours (like the 3 letter search pattern) were kept so applications and scripts built in the "old days" or by "old timers" wouldn't break.

(another example is the fact most windows file systems are case insensitive, yes, you guessed, because the MSDOS one didn't have casing)

Answer 2

If you want a workaround, you could simply retrieve all the file paths

var files = Directory.GetFiles(@"C:\tmp123");

and then filter them by extension as needed

var txtFiles = files.Where(f => f.EndsWith(".txt"));
var txtxFiles = files.Where(f => f.EndsWith(".txtx"));