bash - How to get the last character of a string in a shell?

Question

I have written the following lines to get the last character of a string:

str=$1
i=$((${#str}-1))
echo ${str:$i:1}

It works for abcd/:

$ bash last_ch.sh abcd/
/

It does not work for abcd*:

$ bash last_ch.sh abcd*
array.sh assign.sh date.sh dict.sh full_path.sh last_ch.sh

It lists the files in the current folder.

Answer 1

Per @perreal, quoting variables is important, but because I read this post like 5 times before finding a simpler approach to the question at hand in the comments...

str='abcd/'
echo "${str: -1}"

Output: /

str='abcd*'
echo "${str: -1}"

Output: *

Thanks to everyone who participated in this above; I've appropriately added +1's throughout the thread!