错误描述：运行shell脚本，报错误

test.sh: 4: test.sh: let: not found

解决办法：

It's because Ubuntu uses the dash shell as default and doesn't always recognize when you try to set the shell in a script. Even if you enter "echo $SHELL" into the console it will tell you you're using /bin/bash but for some reason it's actually using dash instead.

use:
sudo dpkg-reconfigure dash
<password>
and when you get the option select "no" to actually use bash instead of dash