shell打印菱形

#!/bin/bash
read -p "input the length: " n
for i in `seq 1 $n`
do
    for ((j=$n;j>=$i;j--))
    do
        echo -n " "
    done

    for((m=1;m<=$i;m++))
    do
        echo -n "* "
    done
    echo

done

for i in `seq 1 $n`
do
    for((j=0;j<=$i;j++))
    do
        echo -n " "
    done

    for((k=$i;k<$n;k++))
    do
        echo -n "* "
    done
    echo
done