--- rxvt-unicode/src/perl/background	2022/11/29 05:01:50	1.107
+++ rxvt-unicode/src/perl/background	2022/11/29 05:45:43	1.108
@@ -1452,7 +1452,7 @@
 # helper function, quote string as perl without allowing
 # any code execution or other shenanigans.
 sub q0 {
-   "qq\x00\Q$str\E\x00"
+   "qq\x00\Q$_\E\x00"
 }
 
 sub old_bg_expr {