df 命令输出虽然内容是正确的, 但是很难阅读

#!/bin/bash

declare counter1
declare counter2
let $counter1 = 1
while [ "$counter1" -lt 6 ]
do echo "Warning: There is a bug in your programme."
let $counter2 = 1
while [ "$counter2" -lt 200 ]
do let $counter2 ="counter2 + 1"
done
clear
let $counter2 = 1
while [ "$counter2" -lt 200 ]
do let $counter2 = "$counter2 + 1"
done
let $counter1 = "$counter1 + 1"
done

./testwhile: 行 5: let: =: 语法错误: 期待操作数 （错误符号是 "="）
./testwhile: 第 6 行: [: : 期待整数表达式

赋值时，请不要在等号两边加空格。谢谢
感觉好多错哦。