Often you need to remove one or many character at the end of a string, but you don`t know the string lenght. When that happen there is a way to extract the character that you want no matter the lenght.
For that technique to work you need to use rev and cut , rev is a program that reverse the string it received and cut is a tool that extract part of string , either by field or by character.
In this example I will show you how to extract the last 4 charactere of a string.
Echo $string | rev | cut -c 1-4 | rev
echo $string ----> Send string to standard output.
rev ----> Reverse the string.
cut -c 1-4 ----> extract character one to four.
rev ----> Reverse the string again to put it back in the orginal order.