DOS string replace and remove character at end

I have a batch script that accepts as the argument a  directory. I need to first check to see if the last character of the string ends with \ and remove it, if it does. I also need to replace all \ with /. I attempted a solution for this second part but it paritally works. It will remove the data before the : and replace all \ with / but I do not need the data prior to the : removed.

Below is my batch script:

@echo off
IF %1=="" GOTO DEFAULTDIR;
SET dir=%1%
GOTO MAINPROCESS;

:DEFAULTDIR
SET dir=%~p0
#replacing \ with /
set dir=%dir:\=/%
ECHO Using %dir% as parent path

:MAINPROCESS

set jardir=%dir%jars
echo Jar directory is %jardir%
echo Completed

:DONE
ECHO DONE

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