China DOS Union

After booting a DOS boot disk made from a USB flash drive into MS-DOS7.1, on some machines its drive letter is “A:”, while on other machines its drive letter is “C:”.
In the batch file autoexec.bat on the USB flash drive, when the drive letter of the USB flash drive is “A:”, program A needs to be executed; when the drive letter of the USB flash drive is “C:”, program C needs to be executed.
How can I get the drive letter of the USB flash drive in the DOS batch file autoexec.bat to make this work?
Thanks in advance!

Solved using the method introduced in post #4.

Thanks again for the answers from the helpful members!

[ Last edited by chenqiguang on 2006-12-27 at 10:28 PM ]

I can't answer the OP's question.
But I can provide one method I use for reference:
In “autoexec.bat”, set the program execution path like this:
SET PATH=A:\dos_tool\;A:\;\C:\dos_tool\;C:\
After that, when executing a program, just write the program name directly.
For example:
LH CTMOUSE
LH DOSKEY
There is no need to call the program with an absolute path. That will do.
As for the reason for the difference between A and C drives, it is related to the way the bootable USB flash drive is made.
With the zip/FDD method, after booting it becomes drive A
With the HDD method, after booting it becomes drive C.
If anything is incomplete, you can contact me by E-mail for discussion.
zplinux@21cn.com

The program to be executed needs parameters, so an absolute path must be used.

You can put a signature file in the root directory of your USB flash drive and use it for detection.
Suppose the file is myudisk.000
if not exit a:\myudisk.000 goto c
a
goro exit

:c
c

:exit

[ Last edited by lianjiang2004 on 2006-12-27 at 03:50 AM ]

This problem is very simple. I also ran into it when making a bootable USB flash drive. The USB flash drive was originally ZIP, but some motherboards insist on recognizing it as drive C: after booting, so the drive letter of the boot disk has to be identified.
There are two methods:
1. Signature detection, FOR %%A IN (A: C:) DO IF EXIST DOS\DRIVERS\NUL SET BDR=%%A （DOS\DRIVERS is a directory on my USB flash drive）This way the boot drive letter can be set into the %BDR% variable.
2. Use a small tool: bootdrv.com. After running it, it will return an errorrlevel value, and by testing that you can know the boot drive letter.