Details of error reporting are as follows
root@OpenWrt :~# /root/connect_ net.sh
-ash: /root/connect_ net.sh: not found

When running a script, the above error occurs. The variables in the script are defined as
code = curl - O/dev/null - SW% {http_code} www.baidu. Com

After querying, it is found that the shell only supports ash in openwrt, while Bash is used by default in Linux and Ubuntu

The solution here is when defining variables, the left and right sides of the equal sign '=' are not left blank, as shown in the example
code = curl - O/dev/null - SW% {http_code} www.baidu. Com

The operation of variables in openwrt still needs attention

variable operation only supports expr, not $[], $(()), let. These three formats must leave a space around the plus sign “+”