(or "In dash, ... is not supported." when using
#!/bin/sh let x=2+2
$((arithmetic expansion)) instead of legacy
let is a command used for arithmetic in some shells, but it's not a standard command. Use
If you only intend to target shells that supports this feature, you can change the shebang to a shell that guarantees support, or ignore this warning.
You can use
# shellcheck disable=SC3000-SC4000 to ignore all such compatibility warnings.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.