How MS-DOS 6.22 Handles Wildcards in CD

In MS-DOS 6.22, the internal change directory command (cd or chdir) natively supports wildcards such as * and ? to simplify folder navigation. Instead of requiring an exact path name, the command processor evaluates the wildcard pattern against the disk's directory table and automatically switches to the very first matching directory it encounters.

The Under-the-Hood Process

When a user issues a command like cd pro* or cd d?r, COMMAND.COM does not perform shell-expansion like modern Unix shells. Instead, it directly invokes the DOS File Find system call via software interrupt INT 21h, Function 4Eh (Find First Matching File).

During this call, MS-DOS 6.22 passes an attribute mask of 10h (the sub-directory attribute), along with the wildcard string. The operating system parses the current directory's table within the File Allocation Table (FAT) file system, scanning sequentially from the beginning of the cluster list.

Directory Order vs. Alphabetical Order

Because COMMAND.COM only calls the "Find First" routine and does not execute a "Find Next" (INT 21h, Function 4Fh), it resolves to the first entry written to the disk table that matches the criteria.

Crucially, MS-DOS file systems do not store directories alphabetically; they are stored in the order they were created or where deleted entry slots were reused. For example, if a directory named PROJECTS was created after a directory named PROGRAMS, cd pro* navigates to PROGRAMS only if its directory record appears earlier on the disk. If PROJECTS was created in an earlier vacated directory slot, cd pro* navigates to PROJECTS instead.

Attribute Filtering and Error Conditions

The system ensures that files matching the wildcard do not cause a false navigation attempt. When scanning the directory entries, the operating system checks the attribute byte of each match:

• Subdirectory Match: If the matched entry has the directory bit set (10h), the path buffer in DOS is updated, and the current working directory changes successfully.
• File Match: If an entry matches the wildcard pattern but lacks the directory attribute (such as a standard file named PROJECT.TXT), the internal search skips it and continues checking subsequent entries until a genuine directory is found.
• No Match: If the scan reaches the end of the directory structure without finding a matching entry that carries the directory attribute, MS-DOS halts the routine and displays the standard error message: Invalid directory.