Atari DOS 2.5: XF551 Owner's Manual page 31

Except lor the period that separates the filename proper from the
optional extender, all the characters in a filename must be letters
or numbers , not punctuation marks or other symbols. So you
could use-
these filenames :
PROGRAM.6J
ACCT4321
LETTER1
but not these:
PROG.6J .BAS
ACCOUNT4321
If
you try to enter an invalid filename, DOS refuses to accept it
and displays ERROR 165 on your screen .
Extenders , sometimes called file types , can be useful when
you ' re naming related but distinct files that you might want to
manage as a group (see " Wild Cards"). For example, you could
use BAS as an extender when naming all programs you write in
ATARI BASIC- PROGRAM1 .BAS , PROGRAM2 .BAS , and so on .
You might use LETTER .BUS to identify a business letter, and
LEITER.SIS for a letter 10 your sister. If you were writing a book
with a word processing program , you might store the various
chapters on diskette as CHAPTER .1, CHAPTER .2, and so forth .
Wild Cards
In a game of poker, wild cards are valuable because they stand
for any card you choose. Similarly, DOS recognizes special wild
card symbols that can stand for any character or combination of
characters in a filename. A major convenience , wild cards en·
able you to refer to a group of files rather than to each one ind io
vidually.
The two wild cards recognized by DOS are the question mark (?),
which stands for any single character, and the asterisk
(*),
which
stands for any combination of characters in a filename proper or
in an extender. Working with the following files, for example , you
could also use PROGRAM?' to specify all the program files ,
including PROGRAM1.PIL. The file LEITER?BUS would refer
to all the business letter files.
PROGRAM1.BAS
PROG RAM2 .BAS
PROGRAM3.BAS
PROGRAM1.PIL
LETTER1 .BUS
LETTER2.BUS
LETTE R3.BUS
LETTER.SIS
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