MacOS default group is not user name.

setup.sh

@@ -2,6 +2,12 @@
 set -e
 PROJECT_PATH=$(dirname $0)
 WHOAMI="$(id -un)"
+if [ "$(uname -s)" = "Linux" ]
+then
+    MYGROUP="${WHOAMI}"
+else
+    MYGROUP="staff"
+fi
 
 if [ $(id -u) -eq 0 ]
 then
@@ -20,10 +26,10 @@ check() {
 
 setup_base() {
     printf 'Change ownership of "%s" to "%s"? (setup may fail otherwise)\n' "${PROJECT_PATH}" "${WHOAMI}"
-    printf 'running: "sudo chown -R %s %s"\n' "${WHOAMI}:${WHOAMI}" "${PROJECT_PATH}"
+    printf 'running: "sudo chown -R %s %s"\n' "${WHOAMI}:${MYGROUP}" "${PROJECT_PATH}"
     if check 'Continue? [Y/n] '
     then
-        sudo chown -R "${WHOAMI}:${WHOAMI}" "${PROJECT_PATH}"
+        sudo chown -R "${WHOAMI}:${MYGROUP}" "${PROJECT_PATH}"
     fi