shell脚本-统计字符串中数字字母的个数

#!/bin/bash

read -p "请输入一个字符串:" str
count1=0
count2=0
count3=0
count4=0
num=${#str}
((num--))
for i in $(seq 0 ${num})
do
	ch=${str:i:1}
	echo -n "$ch"
	case $ch in
		[0-9])
			((count1++))
			;;
		[A-Z])
			((count2++))
			;;
		[a-z])
			((count3++))
			;;
		*)
			((count4++))
	esac
done
echo
echo "字符串${str}中有:数字${count1}个,小写字母${count3}个,大写字母${count2}个,其他字符${count4}个"