diff --git a/rc/01-functions.sh b/rc/01-functions.sh
index 74a3627..f47c326 100644
--- a/rc/01-functions.sh
+++ b/rc/01-functions.sh
@@ -90,3 +90,7 @@ function source_try() {
   fi
 }
 
+function true_false() {
+  [[ "${1,,}" =~ ^(1|true|yes)$ ]]
+}
+