What is my MacBook's firmware password after using setregproptool?

Since OLDPASSWORD and CONFIRMPASSWORD are both unset, the command your script executed was:

/Volumes/OS\ X\ Base\ System/Applications/Utilities/Firmware\ Password\ Utility.app/Contents/Resources/setregproptool -m command -p -o

I don't know for certain (and I'm not about to test it), but I'd expect that this has taken "-o" as an argument to the "-p" option, and hence set the firmware password to "-o".

BTW, in addition to removing the spaces after the "=" in assignments, you should also double-quote all references to variables, like this:

/Volumes/OS\ X\ Base\ System/Applications/Utilities/Firmware\ Password\ Utility.app/Contents/Resources/setregproptool -m command -p "$CONFIRMPASSWORD" -o "$OLDPASSWORD"

This will prevent the shell from doing weird things with variables that contain spaces and/or wildcards, or are blank (like OLDPASSWORD in your script).