case "$1" in -?) echo "Usage: $0 [-n]";; -n) echo "Hello World";; *) exit 1;; esac
case "$1" in -\?) echo "Usage: $0 [-n]";; # '-?') echo "Usage: $0 [-n]";; # Also valid -n) echo "Hello World";; *) exit 1;; esac
You have specified multiple patterns in a case statement, where one will always override the other. The pattern being overridden is indicated with a SC2222 warning.
In the example, -? actually matches a dash followed by any character, such as -n. This means that the later -n branch will never trigger. In this case, the correct solution is to escape the -\? so that it doesn't match -n.
Another common reason for this is accidentally duplicating a branch. In this case, fix or delete the duplicate branch.
None. One could argue that having -*|--*) echo "Invalid flag"; is a readability issue, even though the second pattern follows from the first. In this case, you can either rearrange the pattern from most to least specific, i.e. --*|-*) or ignore the error.
When ignoring this error, remember that ShellCheck directives have to go in front of the case statement, and not in front of the branch:
# shellcheck disable=SC2221,SC2222
case "$1" in
-n) ...;;
# no directive here
-*|--*) echo "Unknown flag" ;;
esac
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