You really don't need a Ruby program to accomplish what you are talking about, if I'm understanding right here. (Also, might I recommend bash shell scripting?
It's a fun language to work with.)
And, actually, depending on your computer's configuration, your devices could be listed with values that are different from what would be expected on another Linux machine. Remember to give your cards labels that you can distinguish with easily. An easy way to do this is simply to go to a Windows computer, open Computer from the Start menu, and change the labels of the drives. You could also use gparted to work with your drive labels.
To mount any drive, you will need to open a shell. Type in:
sudo mkdir /mnt/my_card
(where my_card could be card1, mycard, or anything, as long as it's one title (not 'my camera card', but 'my_camera_card' instead). You will need to type in your password.
If all's successful, a new, blank line will appear. Now, you will need to type in fdisk -l. What disk out of that list matches your card best? Is it the label you assigned? If it's anywhere very close, it's probably it. So, let's suppose your card is /dev/mmc1.
In that case, you would type (and note yours will be different than this example):
sudo mount /dev/mmc1 /mnt/my_card
OK--the card is mounted and you can now access it like you would a flash drive or any other device. To find it, open your favorite file manager (Dolphin, Nautilus, etc.) and navigate to, (from the example here), /mnt/my_card. You should find your card's contents spilled out here, and you can now work with your card.
Hope this helps.