Created SC2249 (markdown)

SC2249.md

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+## Consider adding a default *) case, even if it just exits with error.
+
+### Problematic code:
+
+```sh
+case "$1" in
+  start) start_service ;;
+  stop)  stop_service ;;
+  restart|reload|force-reload)
+    stop_service;
+    start_service;;
+esac
+```
+
+### Correct code:
+
+```sh
+case "$1" in
+  start) start_service ;;
+  stop)  stop_service ;;
+  restart|reload|force-reload)
+    stop_service;
+    start_service;;
+  *)
+    echo >&2 "Invalid choice: $1"
+    exit 1
+esac
+```
+
+### Rationale:
+
+ShellCheck found a `case` statement that may not be considering all possible cases. This may mean that only the [happy paths](https://en.wikipedia.org/wiki/Happy_path) are accounted for.
+
+Consider adding a default case to handle other values. If you don't know what to do or don't believe it'll ever happen, exiting with an error is good, fail-fast practice.
+
+The example is adapted from a real world Debian init script, which due to a missing default case reports success on any misspelled command (here with underscore instead of dash):
+
+```
+$ /etc/init.d/screen-cleanup force_reload && echo success
+success
+```
+
+### Exceptions:
+
+This suggestion only triggers in verbose mode (`-S verbose`). 
+
+If you don't have a default case because the default should be to take no action, consider adding a comment to other humans:
+
+```
+case "$(uname)" in
+  CYGWIN*) cygwin=1;;
+  MINGW*) mingw=1;;
+  *) # No special workarounds identified
+esac
+```
+
+If you believe that it's impossible for the expression to have any other value, it's considered good practice to add the equivalent of an `assert(0)` to fail fast if this assumption should turn out to be incorrect in the current or future versions:
+
+```
+case "$result" in
+  true)  proceed;;
+  false) cancel;;
+  *) echo >&2 "Submit bug report: '$result' should be true or false."
+     exit 127
+esac
+```
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!