cmd.exe if you type:
it will copy a.txt* (including a.txt1, a.txtb, etc).
How can I just copy a.txt?
I don't know where you got that idea... DOS (all versions of) does not copy all files that start the same way without using a wild-card character. For example:
will ONLY copy a.txt to that new location. The alternative:
will copy all files starting with