SC3002 – ShellCheck Wiki

In POSIX sh, extglob is undefined.

(or "In dash, ... is not supported." when using dash)

Problematic code:

#!/bin/sh
rm !(*.hs)

Correct code:

Either switch the shebang to a shell that does support extglob, like bash or ksh, or rewrite in terms of a loop with a case or grep match:

#!/bin/sh
for file in *
do
  case "$file" in
    *.hs) true;;
    *) rm "$file" ;;
  esac
done

Rationale:

Extglobs are extensions in bash and ksh, while your shebang says you're using sh or dash.

Exceptions:

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.

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