diff --git a/bash/util.sh b/bash/util.sh
new file mode 100644
index 0000000..e3781a7
--- /dev/null
+++ b/bash/util.sh
@@ -0,0 +1,7 @@
+not() {
+	case "${1}" in
+	"false") echo "true" ;;
+	"true") echo "false" ;;
+	*) ;;
+	esac
+}