string="nhooo is a great site"
echo ${string:1:4}

string="nhooo is a great site"
echo `expr index "$string" io`

arry_1=("我是1" "我是2" "我是3")
echo ${arry_1[1]}
echo ${#arry_1[@]}

my_array=(A B "C" D)
echo "第一个元素为: ${my_array[0]}"
echo "第二个元素为: ${my_array[1]}"
echo "第三个元素为: ${my_array[2]}"
echo "第四个元素为: ${my_array[3]}"

val=`expr 2 + 2`
echo "两数之和为 : $val"