How to remove a specific character from a string, only when it is the first or last character in the string.

Suppose I have a string 1,2,3, I would like to remove the last , or if the string looks like ,1,2,3, or ,1,2,3 I would still like to get 1,2,3 as my result. And please try to be a little explanatory in your answer. I do not just want to copy paste stuff without understanding it. Thank you.