Strange Windows DIR command behavior

Wild cards at the command prompt are matched against both the long file name and the short "8.3" name if one is present. This can produce surprises.

To see the short names, use the /X option to the DIR command.

Note that this behavior is not in any way specific to the DIR command, and can lead to other (often unpleasant) surprises when a wild card matches more than expected on any command, such as DEL.

Unlike in *nix shells, replacement of a file pattern with the list of matching names is implemented within each command and not implemented by the shell itself. This can mean that different commands could implement different wild card pattern rules, but in practice this is quite rare as Windows provides API calls to search a directory for files that match a pattern and most programs use those calls in the obvious way. For programs written in C or C++ using the "usual" tools, that expansion is provided "for free" by the C runtime library, using the Windows API.

The Windows API in question is FindFirstFile() and its close relatives FindFirstFileEx(), FindNextFile(), and FindClose().

Oddly, although the documentation for FindFirstFile() describes its lpFileName parameter as "directory or path, and the file name, which can include wildcard characters, for example, an asterisk (*) or a question mark (?)" it never actually defines what the * and ? characters mean.

The exact meaning of the file pattern has history in the CP/M operating system dating from the early 1970s that strongly influenced (some might say "was directly copied" in place of "influenced" here) the design of MSDOS. This has resulted in a number of "interesting" artifacts and behaviors. Some of this at the DOS end of the spectrum is described at this blog post from 2007 where Raymond describes exactly how file patters were implemented in DOS.

Yep. You'll see that it also searches through short names if you try this:

dir /x *4*

(/x switch is for short names)

for filtering file names use :

dir /b | find "4"

A quote from RBerteig's answer:

Note that this behavior is not in any way specific to the DIR command, and can lead to other (often unpleasant) surprises when a wild card matches more than expected on any command, such as DEL.

The above is true even for the FOR command, which is very nasty.

for %A in (*4*) do @echo %A contains a 4

will also search the short names. The solution again would be to use FIND or FINDSTR to filter out the names in a more reliable manner.

for %A in (*) do @echo %A | >nul findstr 4 && echo %A contains a 4

Note - change %A to %%A if using the command within a batch file.

Combining FOR with FINDSTR can be a general purpose method to safely use any command that runs into problems with short file names. Simply replace ECHO with the problem command such as COPY or DEL.