China DOS Union

Question for everyone:
1. Does anyone have software that can map a folder on a CD as a drive, so that if I type drive_letter: it goes straight to that folder.
2. In a *.bat, how can I set it so that if no key is pressed within a specified time it jumps...
3. Are there any articles introducing return values and variables?
4. What does >nul mean?
5. How can I get the current drive letter as a variable? (That is, how do I know what drive I'm currently on? Don't tell me to use my eyes, hehe)

Many thanks!

1. You can use DOS's built-in SUBST
Usage: SUBST folder path
Remove it with SUBST drive_letter /D
2. Use DOS's built-in CHOICE
For details on CHOICE, enter CHOICE /？ under DOS
3. Don't know, there probably are....
4. >nul means the output is not displayed. In other words, the output content is not shown on the screen. The NUL after it can also be replaced with something else.
For example, AA will store the output result in the AA file.

5. Figure it out yourself

No, that won't work. subst can only map hard disks; mapping a CD gives an error.....

Find another version!