"command not found"

[Buck, Peter INS]

All right, I confess, I fooled with the CygWin B20 shortcut.  Things were
working fine before I did that.  Now, however, when I start Cygwin and type
in things such as chdir or mkdir, I get (for example)

bash: mkdir: command not found.

So I gave up and uninstalled and reinstalled.  Same thing.  I've done that a
couple of times, and made sure that the installation directory was gone in
between.

The shortcut runs the batch file D:\apps\cygnus\cygwin-b20\cygnus.bat (I
installed in a non-standard place, but it worked the first time, I swear it
did).

I took out the "echo off" in the bat file and verified that the path is
getting set.

If I type in "help" I get a page of help, all the local commands.  They
work.

I checked the archives for this list and found references to Cygwinb19.dll.
I don't have one of those, nor Cygwinb20.dll, as I might expect for this
release.  In D:\apps\cygnus\cygwin-b20\cygnus.bat are the dlls 

cygtcl80.dll
cygtclpip80.dll
cygtclreg80.dll
cygtk80.dll
cygwin1.dll
tix4180.dll

It must be simple, but I need a clue.

Thanks,
Peter
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