I had an install of ruby from source on my USB WD Passport drive. Using the ruby install on my portable drive on multiple windows machines requires updating the Path environment variable to reflect the USB drive letter assigned by that particular machine to my drive. The drive letter could be different each time, depending on the machine and the USB port. So I had a crack at writing a .bat file that I can run instead of clicking around and typing the path and drive letter to the ruby /bin directory, I can run this .bat file and it will set the Path for me. It does not seem to stay in the system, which I suppose you would not want it to since the drive letter may be different each time. But I run it from the windows command prompt and then I have ruby available for that shell.
set d = %~d0
ECHO %PATH% | FIND /I "%d%:\lib\ruby\ruby191\bin"
IF ERRORLEVEL 1 SET PATH=%PATH%;%~d0\lib\ruby\ruby191\bin
