Shell: let:not found

let:not found

原因：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.

解决办法：

1.显式使用 dash filename.sh;

2.在命令行输入：sudo dpkg-reconfigure dash

Use dash as the default system shell(/bin/sh)?  选择“no”。