Shell script to find string length

SCRIPT:

#!/bin/bash

echo -n "enter the string : "

read str

length=`expr $str|wc -c`

length=`expr $length - 1`

echo "the length of the entered string $str is $length"

OUTPUT:

sujin@sujin:~/work/shell$ bash find_length.sh

enter the string : linux_ubuntu

the length of the entered string linux_ubuntu is 12