97.正三角形のスクリプトを印刷する

#!/bin/bash
#The script is used to print triangles.
#Date 2021-03-01
#while循环判断输入是否为空，或不为纯数字，二者不符合则重新输入。
while :
do
read -p "Please input a positive number: " num
n1=`echo $num|sed 's/[0-9]//g'`
if [ -z $num ];then
        echo "The input can not be empty."
        continue
elif [ -n "$n1" ];then
        echo "The input must be pure number."
        continue
else
        break
fi
done
#for循环内嵌for循环打印正三角形
for i in `seq 1 $num`
do
        j=$[$num-$i]
        for j in `seq $j`
        do
                echo -n " "#-n不换行打印空格
        done
        for k in `seq $i`
        do
                echo -n "* "#-n不换行打印星号
        done
        echo#换行
done

运行结果：
Please input a positive number: 2
  * 
*   *