What are rules to name a file in MS-DOS?

Answer 1

In MS-DOS, file names can be up to eight characters long, followed by a period and up to three characters for the file extension (e.g., FILENAME.EXT). File names can contain letters, numbers, and certain special characters, but cannot contain spaces or special characters such as \ / : * ? " < > |. Additionally, file names are not case-sensitive in MS-DOS.

Answer 2

The file name must not exceed eight characters separated by a dot having up to three extension letters. Very little punctuation or special characters can be used in the name or extension other than a hyphen, tilda, brace or an underscore. In fact, if the file name is corrupted and a character you cannot type is in the name, it makes it difficult to deal with the files. There was a little trick where some users held down ALT and typed 255 on the number pad and added that character to the name. Others would see a name with a space on the end and then wonder why entering a space doesn't work.

For example:

abcdef12.123

hello.c

readme

are all valid filenames.

Directories usually have a null extension, though they can have an extension. Files don't have to have an extension but usually do.

For example:

dir *. will display mostly directory names.

In later DOS versions, you would do Dir /ad if you want directories so you won't get files that have no extensions nor exclude directories that have extensions. This command might even help find hidden directories.

The 8.3 limits apply to older versions of DOS that use a FAT12 or FAT16 file system. Starting with FAT32, long filename support (LFN) was added, and a few additional characters could be used in the long file names, including spaces, and file names could be up to 64 characters long. However, there were underlying short file names that were there for reverse compatibility, and they still follow the above rules.