This question already has an answer here:
Due me testing out various mods, I've created a cloned .minecraft folder called ".minecraft_modtesting" .
In my normal MC folder I've got a batch file with
start /high javaw -Xmx2048M -Xms1024M -Djava.library.path=bin/natives -cp bin/minecraft.jar;bin/jinput.jar;bin/lwjgl.jar;bin/lwjgl_util.jar net.minecraft.client.Minecraft "name" "password"
However, I can't use this in ".minecraft_modtesting" because it starts the minecraft.jar from the ".minecraft" directory.
How can I change that please?